Coolant in Engine Oil

Easy to follow step by step guide on how to repair coolant in the engine oil, though appearances may vary the concepts are the same for most vehicles.

Difficulty Scale: 5 of 10

Tool and Supplies Needed

  • Flashlight
  • Wrench set
  • Socket set
  • Protective eyewear and clothing

Begin with the car on level ground with the engine "OFF" and "COOL" with the parking brake "ON".

Step 1 - To check for coolant in the oil first remove the oil fill cap and inspect the underside, also look into the engine with a flashlight, if a milky white or yellow colored oil is detected the engine is leaking coolant internally. (Note: If an engine has not been run very much there will be a slight amount of milky oil due to condensation which is not present in engines that are run on a regular basis.) Also, remove the engine oil level dipstick to inspect oil consistency and color, if the oil is milky and yellow, coolant has made its way into the engine.

Please visit our blown head gasket troubleshooting guide for further instructions.

Condensed Coolant Under Oil Cap

Step 2 - A common problem on a "V" style engine is the intake manifold gasket failing allowing coolant into the oiling system, to check for this condition the intake manifold must be removed and gasket inspected.

Intake Manifold Leak

Step 3 - A common failure is the cylinder head gasket, these gaskets can fail allowing coolant directly into the engine, the cylinder head must be removed and the gasket inspected.

Please visit our blown head gasket troubleshooting guide for further instructions.

Head Gasket Surface

Step 4 - When an engine is designed with a coolant style oil cooler it can fail allowing coolant into the engine. After the engine has been run and then shut off the cooling system will have about 15 pounds residual pressure forcing coolant into the engine oil, once repaired the engine oil and filter must be replaced.

Step 5 - If a cylinder head has a crack due to overheating or useage it can allow coolant into various internal engine parts. Please visit our engine overheating guide for further instructions.

Step 6 - If the block becomes cracked it can allow coolant to enter the oil system of the engine, to inspect for this condition the engine must be removed and dissembled.

Helpful Information

Coolant runs throughout the engine block, cylinder heads, intake manifold, (some applications) engine oil cooler (if equipped) hoses, heater core and radiator. The engine cannot run with coolant in the oil system, catastrophic failure will occur. Do not run an engine once coolant is discovered in the engine oil. These repairs can be tricky because they overlap and it can be difficult to tell which one is causing the problem before the repair has begun. Please visit our cooling system guide for further information.


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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