3116 and 3126 Truck Engines Loss Of Coolant

A. Outside Leaks (Go to Step 1)

Probable Cause(s):

* Leaks In Hoses Or Connections
* Leaks In The Radiator And/Or Expansion Tank
* Leaks In The Heater
* Leaks In The Water Pump
* Cylinder Head Gasket Leakage

B. Coolant Leaks At The Overflow Tube (Go to Step 6)

Probable Cause(s):

* Defective Pressure Cap
* Engine Runs Too Hot
* Expansion Tank Too Small
* Cylinder Head Gasket Leakage Or Crack(s) In Cylinder Head Or Cylinder Block

C. Internal Leakage (Go to Step 10)

Probable Cause(s):

* Erosion Or Crack(s) In Unit Injector Sleeves
* Cylinder Head Gasket Leakage
* Crack(s) In Cylinder Head
* Crack(s) In Cylinder Block

A. Outside Leaks

Probable Cause(s):

1. Leaks in hoses or connections:

Check all hoses and connections for visual signs of leakage. If no leaks are seen, look for damage to hoses or loose clamps.
2. Leaks in the radiator and/or expansion tank:

Put pressure to the radiator and/or expansion tank with the 9S8140 Cooling System Pressurizing Pump Group and check for leaks.
3. Leaks in the heater:

Put pressure to the cooling system with the 9S8140 Cooling System pressurizing Pump Group and check for leaks.
4. Leaks in the water pump:

Check the water pump for leaks before starting the engine, then start the engine and look for leaks. If there are leaks at the water pump, repair or install a new water pump.
5. Cylinder head gasket leakage:

Look for leaks along the surface of the cylinder head gasket. If you see leaks, install a new head gasket. Tighten the bolts that hold the cylinder head according to the Specifications Section of the Service Manual.

B. Coolant Leaks At The Overflow Tube

Probable Cause(s):
6. Defective pressure cap:

Check the sealing surfaces of the pressure cap and the radiator to be sure the cap is sealing correctly. Check the opening pressure and sealing ability of the pressure cap valve with the 9S8140 Cooling System Pressurizing Pump Group.
7. Engine runs too hot:

If coolant temperature is too high, pressure will be high enough to move the cap off of the sealing surface in the radiator and cause coolant loss through the overflow tube. See Problem No. 23, Above Normal Coolant Temperature.
8. Expansion tank too small:

The expansion tank can be either a part of the radiator or it can be installed separately from the radiator. The expansion tank must be large enough to hold the expansion of the coolant as it gets warm or has sudden changes in pressure. Make sure the expansion tank is installed correctly, and the size is according to the recommendations of the OEM.
9. Cylinder head gasket leakage, or crack(s) in cylinder head or cylinder block:

Remove the radiator cap and with the engine running look for air bubbles in the coolant. Bubbles in the coolant are a sign of probable leakage at the head gasket. Remove the cylinder head from the engine. Check the cylinder head, cylinder walls and head gasket surface of the cylinder block for cracks. When installing the head, use a new head gasket. Tighten the bolts that hold the cylinder head according to the Specifications Section of the Service Manual.

C. Internal Leakage

Probable Cause(s):
10. Erosion or crack(s) in unit injector sleeves:

If fuel is detected in the coolant, a possible cause is a defective unit injector sleeve. Remove the unit injectors and inspect the sleeves for cavitation erosion or cracks. Replace any defective sleeves.

NOTE: Refer to Disassembly And Assembly, SENR6553, for the proper procedure for unit injector removal and installation.
11. Cylinder head gasket leakage:

If the cylinder head gasket leaks between a water passage and an opening into the crankcase, coolant will get into the crankcase.
12. Crack(s) in cylinder head:

Crack(s) in the upper surface of the cylinder head, or an area between a water passage and an opening into the crankcase, can allow coolant to get into the crankcase.
13. Crack(s) in cylinder block:

Crack(s) in the cylinder block between a water passage and the crankcase will let coolant get into the crankcase.

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