There are several factors which affect the amount of material that can be removed from the surface of a cylinder head. These include valve projections, surface flatness and finish. Measure these areas as well as the cylinder head minimum thickness dimensions whenever you recondition the head to block mating surface.
Before cleaning or machining of the cylinder head bottom deck, remove fuel injection nozzles/adapters from the head. On occasion, intake and exhaust valves may also require removal. Machining this surface can be accomplished with a mill, surface broach machine or surface grinder.
NOTE: Remove the minimum amount of material necessary to make the repair. Minimum head thickness following machining is 98.89 mm (3.893 in).
Machined surfaces must be smooth to form a good seal. The surface finish of the cylinder head faces must be as smooth as a new head after machining. Cylinder head flatness must not vary more than 0.10 mm (0.004 in) overall, or 0.05 mm (0.002 in) for any 152 mm (6.0 in) span.
Cylinder head flatness can be measured by using a 610 mm (24 in) straight edge for measuring the total length flatness and a 152 mm (6 in) straight edge for measuring across the sealing surface.
* Place the straight edge on the sealing surface.
* Use the feeler gauge and very carefully slide it under the straight edge.
NOTE: Clean machining debris from internal head passages prior to reassembly.
After the cylinder head has been reconditioned, you must measure the valve projection. The maximum and minimum projection specifications for intake and exhaust valves are listed in the Service Manual for the engine. Excessive projection can cause the valve head to contact the piston during engine operation.
Cylinder Head – Bottom Deck
Remove the cylinder head from the engine to expose the bottom deck sealing surface. Before cleaning or machining of the cylinder head bottom deck, remove fuel injection nozzles/adapters from the head. Use a putty knife to scrape off any excess gasket material. With the valves still in place, thoroughly clean the bottom deck with a wire wheel or “Scotchbrite” pad. Use solvent or 8T9011 Component Cleaner to remove any oil, grease or loose carbon from the combustion surface and wipe clean.
If a metal reconditioning disk is used to remove gasket material, caution should be used to not remove any metal. If used too long in a small area, metal may be removed which may affect sealing surfaces.
Visually inspect the bottom deck of the cylinder head for damage. Determine if the combustion surface flatness is within specification. Occasionally, the head gasket fire ring sealing surface can suffer erosion or “Beat-In” following a gasket failure. If a depression can be felt in this area with the fingertip or fingernail, measure the depth with a 8T0455 Liner Projection Tool Group. Be sure the tool dial indicator is correctly calibrated before use.
If erosion or fire ring “Beat-In” exceeds 0.025 mm (0.001 in), the cylinder head combustion surface must be repaired by machining or the head replaced.
Erosion around the water hole is not critical if there is enough material left to support the water ferrule. Erosion in this area can sometimes be corrected with a room temperature vulcanizing (RTV) compound used to help seal the water ferrule.
Coolant loss and aeration can be caused by reasons other than combustion gas leakage past the head gasket fire ring seal.
Air can enter the system by:
Filling the system improperly.
Allowing the coolant level to drop too low.
Improper coolant system maintenance.
Venting the system improperly.
Through a cracked air compressor head.
Any cooling system leakage points.
Combustion gases can enter the cooling system at:
The head to block joint.
An injector adapter/seal.
A cracked cylinder head.
A cracked cylinder liner flange.
Through a pitted cylinder liner.
One way to detect air or combustion gases entrance in the cooling system is to visually inspect the system’s components.
The simplest is to check the coolant level. Significant coolant aeration is unlikely if the system is full and no coolant has recently been added. If it is low, there may have been an overflow discharge, a result of air or gases in the cooling system.
A more thorough procedure is to pressurize the system [75 to 103 kPa (11 to 15 psi)] and check for external leaks:
Hoses and lines.
Clamps and connections
Water pump seal.
Radiator core, header and tanks.
Gaskets and drain plugs.
All of these could be sources of leaks and should be repaired immediately.
A properly functioning radiator cap is crucial to sealing and maintaining the cooling system pressure. If the cap is not seated tightly in the filler neck or the pressure relief valve opens at a pressure that is too low, the system pressure and the boiling point of the coolant will be reduced. This can allow coolant to escape through the overflow hose.
It is very important to make sure the cooling system is filled to the proper level. BE CAREFUL NOT TO OVERFILL THE SYSTEM. It will purge itself to reach equilibrium and coolant will be discharged through the overflow.
When the radiator is filled initially or when the coolant is changed, premixed coolant should be added no faster the 20 liters (5 gallons) per minute, This reduces the chance of trapping air bubbles in the system and causing the coolant level to be too low.
Inspect the coolant level in the top tank. Bring the coolant to the proper level before testing.
An easy method to test for air or combustion gases in the cooling system is the Pressure Test using a pressurizing pump with a gauge, part no. 9S8140 or equivalent.
Remove the pressure cap and run the engine until the thermostat opens and the engine reaches operating temperature of 91 to 100°C (195 to 210°F). This will vent the normal coolant expansion.
After the temperature stabilizes install the pressurizing pump and gauge kit.
Use the pump to pressurize the system to nominal pressure of 35 to 50 kPa (5 to 7 psi). Continue to run the engine at a constant temperature and rpm (between 1500 to 1800 rpm) and monitor the gauge.
Because the pressurizing kit does not have an automatic pressure relief valve do not exceed 103 kPa (15 psi) or cooling system components may be damaged.
If the pressure reaches 75 kPa (11 psi) or greater within 5 to 10 minutes release it back to 34 to 48 kPa (5 to 7 psi). If the pressure rises again to 75 kPa (11 psi) or greater there probably is an internal leak that will require removal and inspection of cylinder head, gasket, injector adaptors or cylinder liners.
If there is no combustion gas leak, the gauge will remain at 34 to 48 kPa (5 to 7 psi), varying approximately 7 to 14 kPa (1 to 2 psi) when the fan comes on.
Air and gas in the system can also be checked by another simple test called the Bottle Test.
The equipment needed to perform this test is a bucket of water, a calibrated half liter or pint bottle and a length of hose attached to a modified radiator cap.
After the pressure test the engine should already be at operating temperature [90°C to 99°C (195°F to 210°F)] and the expansion air and gases vented. Install the modified radiator cap and hose. Submerge the bottle in the bucket, filling the bottle completely with water. Invert the bottle keeping the mouth under water. Place the loose end of the hose into the water-filled bottle.
Continue to run the engine at constant temperature and rpm (between 1500 to 1800 rpm). If there is a combustion gas leak, the gases will make their way to the radiator, through the hose and into the inverted bottle.
If more than 0.5 L (0.13 gal) of water per minute is displaced, air or gas entering the cooling system is excessive. Under a load condition on a dyno, 0.75 L (.195 gal) per minute would be excessive. There is probably an internal leak that will require removal and inspection of the cylinder head, gasket, injector adaptors or cylinder liners.
These instructions cover the installation of 3S6610 Cage in place of 2S1489 Cage or 2S4699 Cage in water pumps on both 4 and 6 cylinder, 4.5″ bore engines. When either former cage is ordered, 3S6610 Cage will be furnished with 7F2122 and 6F5559 O-ring seals and 2S3279 Gasket. The O-rings are to be installed on the water pumps of 4 cylinder engines and the gasket is to be installed on the water pumps of 6 cylinder engines.
1 Remove the water pump as outlined in the Service Manual. Install the new cage and O-rings (1) and (2) on 4 cylinder engines.
2 Install the new cage and gasket on 6 cylinder engines.
3 Install the water pump on the engine.
3300, 3400 Series and 6.25″
Bore Vee Engines
This instruction gives the procedure for inspecting and installing water pump seal groups.
Correct inspection and installation procedures can help to prevent unneeded replacement of engine water pump components.
Use the chart that follows to find the correct seal group and installation tool for a given engine.
Reference: Operation and Maintenance Guide, Parts Book, Service Manual.
1. Remove and disassemble the water pump as shown in the Service Manual.
2. Remove the old seals, and use steel wool to clean the shaft.
NOTE: Some corrosion and/or deposits on pump shaft (1), where carbon seal assembly (2) and ring (3) meet, is normal and does not require replacement of shaft (1).
A polished area on water pump shaft (1) indicates that carbon seal assembly (2) has been spinning on shaft (1). Use 240 grit emery cloth to clean the area before installing a new seal assembly.
3. Use a micrometer to measure pump shaft (1) at location (A).
NOTE: For the correct fit of carbon seal assembly (2), the shaft diameter must be:
* 19.10 mm (0.752″) ± 0.05 mm (0.002″) for 3300 and 3400 Series Engines.
* 25.45 mm (1.002″) ± 0.05 mm (0.002″) for 6.25″ Bore Vee Engines.
4. Install a new oil seal (4) in housing (5) as shown in the Service Manual.
5. Install shaft (1) and bearing as shown in the Service Manual.
NOTE: All 3400 Series Engines must have clearance between the water pump seal group and impeller counterbore (B). If there is interference, machine impeller counterbore (B) diameter to 34.30 mm (1.350″) ± 0.051 mm (0.0020″) or install a new impeller.
6. Use 6V1541 Quick Cure Primer to clean shaft (1) and counterbore (C) in pump housing (5).
7. Use the non-counterbored end of installation tool (6), and install ring (3) and the seal in housing (5).
NOTE: See the chart on the opposite page for the correct installation tool.
8. Remove the spring, and dip carbon seal assembly (2) in clean water.
NOTE: Use clean water only to reduce the friction between the seal rubber and shaft (1).
Do not get any oil or grease on the face of the seal.
9. Use the counterbored end of installation tool (6), and press (by hand) seal assembly (2) onto shaft (1) until the carbon seal face makes light contact with the face on ring (3).
NOTE: See the chart on the opposite page for the correct installation tool.
The carbon seal assembly must rotate with the water pump shaft.
10. Install the carbon seal assembly spring.
11. Complete the assembly and installation of the water pump as shown in the Service Manual.
After the assembly is complete, get the engine ready for use as shown in the Operation and Maintenance Guide.
Machines With Air-To-Air Aftercoolers or Oil-To-Air Oil Coolers
SERVICE MAGAZINE, SEPTEMBER 5, 1977, PAGE 5, “Field Repair of Cooler Cores Made of Aluminum”. There is a recommendation in this article that carbon tetrachloride can be used to clean small repair areas of the cooler core. This is wrong. Do not, under any circumstances, use carbon tetrachloride. It is highly toxic and hazardous to your health.
————— END SUPPLEMENT —————
Some cooler cores that are made of aluminum which have been damaged or leak, can be repaired in the field. Repairs can be made with weld or with epoxy. The weld procedure is normally the best for the heavier parts of the cooler cores such as the end, top or bottom tanks, the connections or the support brackets. The epoxy procedure is normally the best for the tube and fin part of the cooler core.
Procedure to Clean Cooler Core Before Repair Is Made.
Remove all paint, oil, grease or dirt from the area that needs repair. A small knife, file, emery paper, wire brush and/or solvent can be used.
Do not use a cleaner that will cause a chemical reaction with aluminum. These types of cleaners will damage the core.
Trichlorethylene or chlorothene nu can be used as solvents to clean the cooler core. Flush the internal part of the cooler core with a solvent. If the area to be repaired is very small the internal parts can be cleaned by pushing either acetone or carbon tetrachloride through the hole.
Use 4043 welding rod and tungsten inert gas welding process. Any part of the cooler core can be repaired with this procedure, but it is normally easier to weld on the heavier sections of the cooler core.
Use a two part epoxy such as Devcon Special-F Repair Kit-aluminum filled, Devcon EK-4 Kit-unfilled, or an equivalent epoxy.
NOTE: Do not mix the epoxy until the cooler core is ready for the repair. If additional parts such as a screw or a screen are needed to make the repair, be sure that you have those parts ready. Do not mix more of the epoxy than is needed to make the repair.
The epoxy in The Special-F Repair Kit has a cure time (amount of time needed for the epoxy to completely dry) of approximately 8 hours and a pot life (amount of time that epoxy can be used after it is mixed) of approximately 20 to 30 minutes. This type of epoxy is normally used on larger repairs.
The epoxy in the EK-4 Kit will set (become rigid but not completely hard) in approximately 15 minutes or it has a cure time of approximately 20 minutes when a 100 Watt light bulb is used to give heat to the epoxy. The epoxy in the EK-4 Kit has a pot life of approximately 5 to 6 minutes. This type of epoxy is normally used on smaller repairs.
The epoxy will take longer to dry if the temperature is less than 65°F (18°C). A 100 Watt light bulb can be used to make the epoxy dry faster if the temperature is below 65°F (18°C).
Mix equal amounts of each part of the epoxy on a surface that can be thrown away such as a piece of wood or a heavy cardboard. Use a putty knife or spatula to mix the two parts thoroughly. Immediately put the epoxy on the area to be repaired.
If the area is small, it can be repaired by pushing the epoxy into the hole so some of the epoxy goes into the core. Then put epoxy over the hole and the area around the hole.
If the hole is larger, it can be repaired using a sheet metal screw. First push epoxy into the hole. Then install the sheet metal screw and put epoxy over the screw and the area around the screw. Be sure the head of the screw and the area around the screw is completely covered with epoxy.
If the damage is on the side wall of the tube, use paper, gum or modeling clay to fill the area over and around the hole and between the tube and fin. Then put epoxy over the paper, gum or modeling clay on both sides of the cooler core. Be sure there are no bubbles in in the epoxy or air between the epoxy and the paper, gum or modeling clay. This can cause a leak.
If the damaged area is large, a piece of aluminum screen, thin aluminum plate with a few holes or aluminum foil with a few holes must be used with the epoxy. First remove the fins around the damaged area with a sharp wood chisel. Clean the damaged area again. Put epoxy over the damaged area and then put the piece of aluminum screen, plate or foil over the damaged area. Fasten the screen, plate or foil by putting string, wire or hair pin clips around the tube or tubes. Then put epoxy over the damaged area and all of the pieces that were fastened over the damaged area. Be sure the damaged area and the pieces over the damaged area are completely covered with epoxy.
After the repair, remove all epoxy from any tool immediately. If the epoxy becomes hard, it is very difficult to remove.
Do not use the cooler core until the epoxy has become completely hard. Also, do not use epoxy after it has started to become hard.
To improve the appearance (way it looks) of the cooler core, make bent fins straight with the use of pliers. Also, if a fin has been removed, make a replacement fin from thin aluminum plate. Bend the plate to the shape of a fin. Fasten the new fin to the cooler core with epoxy.
Some Caterpillar products use oil coolers which are constructed with nonmetallic parts. These oil coolers are referred to as “Rubber End Sheet” oil coolers because the end plates, which support the tubes, are of a rubber like material instead of metal. There are also nonmetallic baffle plates inside these oil coolers.
Incorrect cleaning solvents can damage these baffle plates. The most common ways of cleaning engine, transmission and hydraulic oil coolers are steam cleaning, caustic solutions and various solvents. Normal hot caustic solutions used on “boil out” tanks do NOT affect the materials in these coolers. Oakite and Magnus brand caustic solutions have been tested and do not damage the parts. Such caustic solutions must be flushed out with a suitable solvent. Some solvents can affect the nonmetallic baffle plates. The baffle plates may swell and crack if an incorrect solvent is used.
DO NOT use chlorinated solvents when flushing oil coolers with rubber end sheets. Use only solvents of the mineral spirits family. Stanisol is an acceptable mineral spirit solvent. Use the solvent only as long as needed. The oil cooler must be completely flushed with clean water after a solvent has been used. Use compressed air to dry the oil cooler and apply a rust preventive if the oil cooler is not to be installed immediately.
If vendors are cleaning or flushing oil coolers for you, check to see what solvents they are using before sending them rubber end sheet oil coolers.
All Caterpillar-Built Gas Engines
Caterpillar-built gas engines are being used more and more in gas compression units for petroleum applications. As a result, both users and dealers desire information on approved fuels for these engines. This information is necessary because many of the compressor engines burn wellhead gas, and the components of wellhead gas are different from location to location. Some of the components can cause shortened engine life.
Dry Natural Gas
Dry natural gas, also known as commercial pipeline natural gas, is a mixture of methane, ethane, propane and butane. The contents of propane and butane are less than 5 percent and 1 percent respectively.
The reference to “dry” is made because the gas has no liquid propane or liquid butane.
The heat content of dry natural gas may change from source to source. Caterpillar-built gas engines are adjusted at the factory with dry natural gas that has a low heat value of 33.72 kJ/I (905 Btu/ft3).
Field gas, also known as wellhead gas, is the gas available at the wellhead in a gas field.
The contents of wellhead gases change from location to location. As a result, the gas from one field may be acceptable for a Caterpillar-built engine while the gas from a different field may not. For this reason, a gas analysis is necessary to find if the fuel should be used.
Wellhead gases which have a minimum of 90 percent methane and ethane and have a remainder no heavier than butane can be used in low compression engines. However, many wellhead gases have some heavier hydrocarbons such as pentane, isobutane and other “gasolines”. These heavier hydrocarbons cause knock and other mixture problems, and they can have negative effects on an engine’s performance and service life.
Sour gas is gas that contains sulfur compounds such as hydrogen sulfide (H2S). Gases that have no sulfur compounds are known as sweet gases.
The use of gases that have hydrogen sulfide can damage the engine. Water vapor and sulfur oxides, which are products of combustion, chemically unite to make sulfurous and sulfuric acids. These acids destroy internal engine components such as oil coolers, valve guides, piston pin bushings, piston rings and cylinder liners. History has shown that oil coolers often are the first components affected by the acids.
Before sour gas is used to fuel an engine, the gas should be analyzed. If it has more than 0.1 percent by volume of hydrogen sulfide, the gas should be cleaned (scrubbed) to decrease the hydrogen sulfide content to below 0.1 percent.
When sour gas is used, steps should be taken to decrease the effects of sulfur compounds. Caterpillar’s recommendations are:
1. Keep the engine outlet coolant temperature between 88° and 93°C (190° to 200°F). A temperature increase of 8.3°C (15°F) across the engine is acceptable, but an increase of 5.6°C (10°F) is best. Lower jacket water temperatures permit water vapor and hydrogen sulfide to condense on the cylinder liners and make acids. Higher temperatures will decrease this condensation.
Generally, engines equipped with inlet-controlled cooling systems will keep the coolant in the correct temperature range. Engines equipped with outlet-controlled cooling systems may need added external controls to keep the coolant temperature within the acceptable range.
A set of thermostatically-controlled shutters on the engine coolant radiator or heat exchanger is the most effective device for controlling the engine temperature. Shutters should be considered for installations designed to operate on sour gas. Some field gathering units which are subjected to overcooling because of cold ambient temperatures, wind, rain, etc., may require an enclosure or a building for adequate temperature control.
A second method for increasing the coolant temperature is to install a temperature regulator with a higher setting. Such regulators are available from Caterpillar and from other suppliers. A list of regulators and sources is available from Caterpillar.
2. Keep the engine oil temperature high enough to prevent condensation of water vapor in the oil. Generally, if the coolant temperature is kept above 88°C (190°F), vapor will not condense in the oil.
3. A CD grade oil which has a sulfated ash content of less than 1 percent should be used in the engine. The CD oil has a higher Total Base Number (TBN), or alkalinity reserve, to neutralize the sulfurous and sulfuric acids better than the oils generally used in natural gas engines.
4. The oil should be regularly analyzed for its Total Acid Number (TAN or the acidity of the oil), nitration, oxidation, pentane insolubles and viscosity increase. The analysis will find early indications of engine problems. Also, it will make sure that the change intervals are not extended beyond the oil’s ability to provide protection for the engine. The amount of make-up oil added to the engine also can affect the oil’s condition. The oil should carefully be monitored.
5. When possible, the engine should be started and brought to operating temperature on sweet gas, then switched to sour gas. To shut off the engine, switch to sweet gas and run the engine for 10 minutes at full load. Then, remove the load and run the engine at half the rated speed for five minutes. Finally, slow the engine to low idle for 30 seconds and shut it off. This procedure will decrease condensation at lower engine temperatures during start-up and shut down.
Propane is a heavier-than-air gas that is moved in a liquid state to a job location and is transformed into a vapor at the location. Since some states will not permit the use of liquid propane inside a building, Caterpillar’s recommendation is to check local building codes before final plans are made for a propane system.
Propane which is 95 percent pure with the remainder no heavier than butane and meets HD-5 specifications can be used in all naturally-aspirated or turbocharged and aftercooled engines. However, all high compression configurations must be used only in no-lug applications.
Commercial bottled fuels such as liquid propane and liquid bottled gas may not meet HD-5 specifications.
Propane-butane is a commercial mixture in which the butane content is more than 5 percent by volume. This mixture should be used only in naturally-aspirated engines with low compression ratios.
Propane-air mixtures, which have the same Btu contents as natural gas, are generally used as a standby fuel or as peaking fuels for natural gas systems. The same pressure regulating systems can be used for both propane-air and natural gas. But, the timing must be adjusted for propane because the ignition qualities of propane are present.
Other mixtures some times used are field gas and wellhead gas which have 5 percent or less butane and have less than 1 percent heavier hydrocarbons.
Other sources of information on fuels and lubricating oils which are available from Caterpillar are:
Petroleum Engine Application And Installation Guide, LEBW2177
EMA Lubricating Oils Data Book, SEBU5939
Fuel Gases For Gas Engines, LEO21242-01
Gas Engine Application And Installation Guide, LEBH2363
Caterpillar’s recommendation is to use these sources when specifications are written for applications which used wellhead or sour gas. Additional information is available from Caterpillar.
Use Correct Procedure To Clean The Engine Lubrication System If Permanent Type Antifreeze (Ethylene Glycol) Is In The Engine
All Engines Using Ethylene Glycol in Coolant System
When there is a cooling system leak into the oil system, it is important that the leak be found and repaired rapidly and that the lubricating system be cleaned before the engine is put back into operation.
Customers who use Scheduled Oil Sampling can find leaks very soon and many times can clean the engine with just an oil and filter change.
There are probably four coolant leak conditions which can be found in the field and the procedure to use to clean the engine lubrication system is different for each:
1. A positive glycol indication in oil analysis coming from oil additives in new oil. Do an oil analysis on a sample of new oil of the same type the customer uses in the engine. Some oils will test positive in an oil analysis since they contain an additive which gives a positive result to the test for ethylene glycol. The time for color change in oil test will be same for new and used oil.
2. The oil analysis shows a small amount of ethylene glycol in the engine lubricating oil, and there are no signs of metal particles or heavy residue on the filters.
Repair the source of the leak and change the lubricating oil and filters. Do not use butyl cellosolve and run the engine to clean it up. Check the filters at a 50 hour interval for any signs of ethylene glycol or metal particles.
3. A check of the lubricating oil and filters shows a heavy, tacky, black or gray residue but no sign of metal particles. This is the way most customers, who do not use oil analysis, find first signs of leakage.
– Find the source of the leak and repair it; or drain the coolant and fill the cooling system with water while a check for the leak is made.
– Install new filters and fill the engine crankcase with a mixture of 75% SAE 30 or SAE 40 oil and 25% butyl cellosolve.
– Put a cover on the radiator until the jacket water temperature is high enough to open the coolant regulators. With the radiator cap removed to keep coolant system pressure at a minimum, run the engine at 75% of the high idle speed no load, to bring the jacket water temperature above the temperature needed to open coolant regulators. Run the engine for 20 minutes at this temperature.
– Stop the engine and inspect the oil filters for any sign of metal particles which are an indication of engine damage. If any particles are found, the engine must be disassembled to determine the area of damage and the necessary steps taken to clean and repair the engine.
– If there are no signs of damage, drain the oil, remove the oil pan and check the cylinder block inner walls and the oil pan. If they are clean, all of the crankshaft bearings should then be inspected for any damage. Inspect all of the bearings. If any damage is seen or more than 33% of the lead tin overlay on the bearings for the crankshaft is worn off of the lower bearing surface, or if the bearings have run more than 2000 hours, install new bearings.
– If the oil pan and cylinder block are dirty after the cleaning process, the best procedure would be to disassemble the engine, clean and repair as needed.
– If bearings are good and engine is found clean, fill the engine with lubricating oil and install new filters. Check the filters at a 50 hour interval for any signs of ethylene glycol or metal particles. If the filters are clean, the normal oil and filter change periods can be used for future maintenance. If signs of ethylene glycol are found, use 50 hour interval oil filter changes and inspection until sludge cleans up. If metal particles are found, the source of the metal must be found immediately.
4. A check of the lubricating oil and filters shows a heavy, tacky, black or gray residue and there are metal particles present on filter or in pan.
Do not use butyl cellosolve and run the engine to clean it up as this can do more damage to the engine. The engine will have to be disassembled, the source of the ethylene glycol leak repaired, the engine cleaned and new parts installed as necessary.
All Caterpillar-Built Diesel Engines
The availability of fuel supplies around the world is changing. To meet the current demand, refineries are now purchasing crude oil from different worldwide sources which include more high sulfur crude oils than before.
The sulfur contents of the refined fuels vary geographically throughout the world from an average of .27 percent by weight to 1.92 percent by weight.
The sulfur content of refined diesel fuels is dependent on the amount of sulfur in the crude oils and on the economics of and/or the refiners’ abilities to remove it. For this reason, the sulfur content of some of today’s diesel fuels is increasing.
The Fuel Sulfur Problem
When diesel fuel is burned in an engine’s combustion chamber, the fuel sulfur is chemically converted to sulfur oxides. These compounds, in turn, react with water vapor to form sulfurous and sulfuric acids. As the vapors condense in the valve guides and in the piston ring area, the acids can chemically attack the metal surfaces and cause corrosive wear.
Neutralizing The Acids
One function of the lubricating oil is to neutralize the acids and, thus, retard the corrosive damage. Certain additives used in lubricating oils contain alkaline compounds which are formulated to neutralize these acids.
The measure of this reserve alkalinity in a lubricating oil is known as its Total Base Number or TBN. The Total Base Number is measured by one of two procedures: American Society For Testing Materials (ASTM) D-2896 or ASTM D-664. Caterpillar’s recommendations are based on ASTM D-2896.
The higher the initial TBN value generally indicates more reserve alkalinity or acid-neutralizing capacity. To minimize corrosive wear caused by increased fuel sulfur levels, engine oils which have higher TBN values are essential.
The New Oil Recommendations
Caterpillar’s new recommendations provide a means of combating the undesirable effects of high sulfur fuels. New guidelines have been developed for the selection of oils that permit STANDARD OIL CHANGE INTERVALS (as per the applicable Maintenance Guide) when using diesel fuels with sulfur contents of up to 1.5 percent.
Caterpillar previously based its standard oil change intervals on a fuel sulfur content of 0.4 percent and recommended shortened change intervals when fuels with greater than 0.4 percent sulfur content were used.
In the past, Caterpillar has recommended specific service classifications of oil, such as API (American Petroleum Institute) Class CD, but has not specified or published any alkalinity reserve (TBN) information. Because the range of TBN values is wide and because there is an increase in the sulfur content of some diesel fuels, it is important that TBN information be readily available. To satisfy this need, the TBN information is now included in the Engine Manufacturers Association’s “Lubricating Oils Data Book For Heavy Duty Automotive and Industrial Engines.” This is available from Caterpillar by Form No. SEBU5939.
The Correct TBN
The first step to determine the correct TBN value is to find the fuel sulfur content. This information should be available from the fuel supplier. If it is not, a fuel sample should be analyzed by a competent, independent laboratory.
When the sulfur content is known, use the graph shown in the illustration to determine the necessary TBN value. For fuels with sulfur content above 0.5 precent by weight, the TBN value should be 20 times the measured fuel sulfur content. The upper broken line is used to determine the necessary TBN value for new oil. New oils having the recommended TBN values will provide acceptable neutralizing performance through the standard change interval.
The lower solid line on the graph provides information needed to determine the minimum TBN value for used oil. The TBN of used oil must be established using the ASTM D-2896 procedure.
Note that the limits increase proportionately with the fuel sulfur contents. Controlled laboratory tests have demonstrated that alkalinity concentrations in critical areas having only small amounts of oil, such as valve guides and piston ring belt areas, must be proportionately higher to effectively neutralize the higher concentration of acids in these areas.
If the fuel sulfur content is not available, use an oil with a TBN of 10 in the United States, in Canada and in the countries where the fuel sulfur content is regulated to 0.5 percent or less by law. In all other areas of the world, including offshore applications, use an oil with a TBN of 20.
Monitoring The Oil
Coping with the effects of fuel sulfur is not a simple task.
Even though the use of proper lubricants and correct change intervals reduces the degree of corrosive damage, engine wear will increase when fuels with higher sulfur contents are used.
Oils which have larger concentrations of acid-neutralizing compounds also have larger ash contents. This may increase deposits on exhaust valve heads and on turbo-charger nozzle rings.
All oils of the same TBN may not perform identically. Oil alkalinity can be achieved through a variety of additives, but some additives simply are more effective against acids than others.
For this reason, the engine should be closely monitored through Scheduled Oil Sampling. If the oil recommendation is followed, but the S.O.S. analysis indicates excessive wear through unacceptable levels of iron (Fe) or chromium (Cr) particles, an oil which has a higher TBN value should be used.
Indications of other elements such as copper (Cu), aluminum (Al), tin (Sn) or silicon (Si) must not be overlooked. Acid corrosion is not the only cause of engine wear. Infrared analysis can determine the degree of sooting, the oxidation level and the amount of sulfur products in the engine oil, which can contribute to engine wear.
Summary Of The Recommendations
For many years, Caterpillar has recommended reduced oil drain intervals as a means of combating the adverse effects of high fuel sulfur. However, data and research now indicate that excessive wear can still occur even when using shortened drain intervals.
For the aforementioned reasons, Caterpillar has developed new recommendations to provide acceptable engine life with the use of higher sulfur fuels. These new recommendations supersede all previously-published oil drain data.
To effectively combat the effects of high sulfur fuels, Caterpillar endorses the following recommendations:
1. Know the fuel sulfur content. Periodically request this information from the supplier, or have the fuel analyzed for sulfur content by an independent laboratory. The fuel sulfur content can change with each bulk delivery. If the sulfur content can not be determined, use the guideline in the second paragraph of Step 2.
2. Select an American Petroleum Institute (API) Class CD engine oil which has the correct TBN value for the fuel sulfur content. Use the graph to determine the correct TBN value.
If the sulfur content is not available, use the following guideline. In the Unites States, in Canada and in the countries where the fuel sulfur content is regulated to 0.5 percent or less by law, use an oil which has a TBN of 10. In all other areas of the world, including offshore applications, use an oil with a TBN of 20.
3. Follow the recommendations and the standard change intervals in the appropriate Maintenance Guide.
4. Maintain a sound Scheduled Oil Sampling program. Monitor the iron (Fe) and chromium (Cr) levels for indications of the lubricant performance. Infrared analysis is an excellent method with which to determine the condition of used oil, along with the ASTM D-2896 procedure to measure the reserve alkalinity (TBN).
Graph for determination of necessary TBN. Find the fuel sulfur percentage on bottom of the graph. Find point where the new oil TBN line intersects the sulfur content line, and read the required TBN at the left side of the chart.