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TROUBLESHOOTING
LOW ENGINE OIL PRESSURE
OIL IN THE COOLING SYSTEM
COOLANT IN ENGINE OIL
Possible Cause
Correction
1. Oil level insufficient. Oil leaking from oil line,
gasket, etc.
1. Check engine oil level. Add oil if necessary. Check for oil leaks.
Repair as required.
2. Incorrect oil viscosity.
2. Drain oil, change oil filters, and fill with the proper grade oil
meeting MACK specifications.
3. Defective oil pressure gauge.
3. Check the operation of the oil pressure gauge. If defective,
replace.
4. Clogged oil filter(s).
4. Replace oil filters. Clean or replace oil cooler. Drain oil and refill
with oil meeting MACK specifications.
5. Engine oil diluted with diesel fuel.
5. Check fuel system for leaks. Make necessary repairs. Drain
diluted oil, change oil filters, and refill with oil meeting MACK
specifications.
6. Defective oil pump.
6. Remove oil pressure relief valve and check condition of seat.
Check that relief valve spring is not sticking, and check for proper
spring tension. Check internal thrust washer. Check cap. Check
assembly parts. Using the incorrect parts will result in incorrect oil
pressure. Make any necessary repairs or install a new relief valve.
7. Oil pump gears not meshing properly.
7. Check mounting arrangement. If the engine has been rebuilt,
check that the gear ratio of the oil pump drive and driven gears
are correct. Incorrect gear combinations will result in immediate
gear failure and possible engine damage.
8. Incorrect oil filter mounting pad gasket.
8. Check for correct oil pad gasket.
9. Excessive clearance between crankshaft and
bearings.
9. Overhaul the engine. Replace any worn/defective parts.
Possible Cause
Correction
1. Defective oil cooler core.
1. Disassemble and repair or replace oil cooler core.
2. Blown head gasket.
2. Replace head gasket.
3. Cylinder head porosity.
3. Replace cylinder head.
Possible Cause
Correction
1. Defective oil cooler core.
1. Disassemble and repair or replace oil cooler core.
2. Cylinder head pipe plug leaking.
2. Repair leak.
3. Cylinder head gasket failure.
3. Pressure-test cooling system and repair as required.
4. Cylinder sleeve seat leaking.
4. Pressure-test cooling system and repair as required.
5. Cracked cylinder head.
5. Pressure-test cooling system and repair as required.
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