Why Engines Are Damaged By Fuel Sulfur

In the past 30 years, fuel sulfur wear in engines has been minimized through the use of correct lubricants, adherence to the correct oil change intervals, and the efforts of the fuel refiners. Recently, we have been receiving reports that fuel sulfur wear is increasing. Many of today’s servicemen and machine operators are not familiar with this type of wear. This article answers some of the questions most frequently asked by engine owners, operators and service personnel.

1. What causes fuel sulfur wear?

Fuel sulfur wear is caused by the corrosive effect of sulfuric acid formed from combustion gases. An explanation of this corrosive wear appears in the February 5, 1979 Service Magazine. (March 7, 1979 Engine News.)

2. How do you recognize fuel sulfur wear?

It causes severe ring and liner wear, plus wear in the exhaust valve guides. Unlike abrasive wear, there will be little or no crankshaft wear. Bearing damage can result from foreign material bypassing the soot-filled oil filters. In very bad cases the bearing surface could show pits.

3. How can fuel sulfur wear be eliminated?

It probably never will be. As long as crude oils contain sulfur, this type of wear can be a problem. But, if you must use high sulfur fuel (and, there will be times and areas where its use cannot be avoided) engine damage can be minimized:

First, through the use of the correct lubricant to protect and clean engine parts. Caterpillar recommends the use of CD quality oil.

Second, by more frequent oil changes. For 30 years Caterpillar has recommended that the oil be changed at ONE-HALF NORMAL OIL CHANGE INTERVALS whenever the sulfur content in the fuel is between .4% and 1%.

4. How can we know we have a CD oil?

Oil quality and type have to be assured by the oil supplier. You can obtain the suppliers’ brand names for CD oil by using Caterpillar Form GEG05044-02, which lists the various oil brands and their quality.

5. Why is there more wear due to sulfur in the past 2 years?

There are several causes:

A. Diesel fuel standards in most countries have always permitted 1% fuel sulfur. However, in the past, fuel suppliers have provided a product under this limit. Now, it is doubtful whether refiners can continue to supply lower sulfur fuel while sulfur increases in the crude supply. Many are now supplying fuel containing almost 1% sulfur.
B. Many users have neglected to change oil according to our recommendations. They had little trouble as long as fuel sulfur was near .6%. Now, with fuel sulfur between .8% and 1.1%, they are experiencing considerable trouble.
C. U.S. and European contractors are moving into jobs in areas with lower quality fuels. Until maintenance practices (such as oil changes) are adjustd to local conditions, heavy wear occurs.
D. If high sulfur fuel is used in an engine with high oil consumption, you may get by with no problems if the shorter change intervals are not used because the continued additions of new oil keep the existing oil in good condition. If a rebuilt engine or a new machine is used with the same extended oil change intervals, problems will result. The new or rebuilt engine will not require much oil addition. This allows the oil condition to deteriorate seriously with the extended change intervals.

6. Why is there so much difference between .5% fuel sulfur and 1.0% fuel sulfur?

Wear is caused by sulfuric acid. The formation of sulfuric acid depends on condensation of sulfur trioxide gas. The condensation point (dew point) varies with the sulfur percentage.

At .4% to .5% sulfur range most of the sulfur trioxide passes out of the engine as gas. As sulfur percentage increases, the dew point becomes higher than engine operating temperature so more acid condenses. Therefore, it is most important to keep the engine cooling system temperature as high as possible and not less than 165°F (75°C).

The wear caused by sulfur, therefore, does not follow a straight line variation. Wear when using fuel with 1% sulfur is at least four times as severe as .5% sulfur.

7. How do I determine the fuel sulfur percentage in fuels available in our service area?

Ask the fuel supplier. He should get this information for you. Use Caterpillar Form SEHS7067 which lists fuel standards and see if any apply to your area. If none of the standards apply, assume you are using 1% fuel sulfur Or, contact the refineries. If possible, have a private laboratory make a test for fuel sulfur. Use test procedures ASTM D1552, D1266, or D129. Fuel sulfur cannot be measured with litmus paper or any simple process.

8. Why are some engines affected much more severely than others?

The ratio of oil sump capacity to horsepower cannot be kept constant for all machines.

For example, the D6D Tractor uses the Caterpillar 3306 Engine with a turbocharger. Thus, the Cat standard oil change interval of 250 hours for turbocharged engines is recommended, even though the engine is set for 140 HP. This engine in the similar 3306 Industrial version can have an approved setting of 250 HP, but uses the same oil pan (sump) and the oil change interval is also 250 hours. When the oil pan is designed for 250 HP and the same pan size is used on the same engine at 140 HP, the engine with the low HP setting will consume considerably less fuel, and therefore considerably less sulfur, than the same engine with the higher HP setting.

It is not possible to select the optimum oil change interval for all applications. We recommend the standard, easy-to-remember oil change intervals of 250 hours for turbocharged engines and 500 hours for naturally aspirated engines. However, it is important to remember that all engines will not respond similarly to the longer oil change intervals when high sulfur fuels are used.

9. Why is the fuel sulfur problem not universal?

The United States and Canada have always removed fuel sulfur. Most Japanese users burn kerosene. Scandanavian countries have supplied .5% sulfur fuel. Now, many countries in Europe are specifying that fuel for land use can only have .5% sulfur. Therefore, these areas have a minimum of potential for trouble with land-based equipment. At sea, all areas could be a problem since land-based standards do not apply to seaports.

10. Do some types of engine applications experience more difficulty than others?

Not really, but the engines in fishing and railroad service usually have longer oil change intervals than other types of service. The fishing industry tends to change oil at the end of each trip. Railroads follow mileage or date change periods. Neither method may relate the change period to the actual oil condition. These applications also idle the engine for long periods, so lower engine temperatures can add to their problem.

11. Can we monitor oil condition?

Yes. Use ASTM procedure D664 to monitor the Total Base Number (TBN). It should not be less than one. Change oil with TBN 1 to 2. Dealers equipped with infrared oil analysis equipment can monitor percent of sulfur in the used oil. If ASTM procedure D2896 is used, a TBN of 3 must be used as the condemning minumum since there is a difference in readout between ASTM D6643 and ASTM D2896. These numbers are applicable for fuel sulfur up to 1%.

12. What is Total Base Number?

It is a measure of the alkalinity of the oil. The alkalinity tends to neutralize the acid products from the fuel sulfur. If the TBN value reaches zero, a strong acid number (SAN) occurs and the attack is very severe.

13. Do new oils have a Total Base Number?

Yes, new CD oils will have a TBN value generally between 7 and 15.

14. Are there other oils that might be used to combat fuel sulfur?

The marine industry has used special marine oils. At this time we do not have experience with these oils. Also, when high TBN marine oil is used with low sulfur, ring stickage occurs. The marine oils do not follow the automotive CD classification system, so until we know more we cannot make a general recommendation.

We hope you find this series of questions and answers informative and see that this information reaches personnel responsible for engine maintenance. It is necessary for all concerned to adjust oil change intervals to the fuel quality being used since there is no improvement in fuel quality likely at this time.

If severe wear is encountered, high fuel sulfur, oil change intervals that are too long, or cooling system temperatures that are too low can be suspected. However, there are other causes for engine wear, so a complete investigation should include the following considerations:

1. Abrasive wear. Look for presence of silicon in oil analysis, dust in inlet manifold, or sand particles in oil pan.
2. Freon gas. Where engines are used to power a refrigerant compressor or in a room with refrigeration equipment, look for freon gas leaks. Freon entering an engine through the air cleaner causes extreme wear.
3. Exhaust gas recirculation. Check on engine installations to be sure exhaust gases are not reentering the engine through the air inlet. Recirculating exhaust gas can cause oil deterioration and corrosion of the inlet manifold. Corrosion particles will then enter the engine.
4. Excessive cooling. More and more diesel engines have a water cooled aftercooler between the turbocharger and inlet manifold to cool the compressed air. When the aftercooler is cooled independently from the engine jacket cooling system, be sure the temperature of the water that leaves the aftercooler is above the dew point of the ambient air. Use a drain valve on the inlet manifold or elbow to periodically drain water which can accumulate while idling. The larger Caterpillar marine engines are equipped with these drain valves.
5. Water leaks inside air aftercoolers. This permits water to enter the engine and increases corrosion and wear.
6. High temperature of air entering engine.
7. Engine overloading or higher than rated engine power settings.

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