Mechanics

Coolant in Motor Oil

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Step by step guide on how to repair coolant in the motor oil. This article pertains to all vehicles except electric.

Difficulty Scale: 4 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 the parking brake on.

Step 1 - To check for coolant in the oil first remove the oil fill cap and inspect the underside while looking 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.)

Step 2 - 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.

Step 3 - When an engine is designed with a coolant 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. The GM manufactured 3.0 V6 in Saturn and Cadillac and VW products are prone to this problem. Once repaired the engine oil and filter must be replaced.

Step 4 - A common problem on "V" style engine is the intake manifold gasket has failed allowing coolant into the engine oiling system. To check for this condition the intake manifold must be removed.

Step 5 - The next most common failure is the cylinder head gasket, these gaskets can fail in two different ways, first: the metal sealing ring in the head gasket fails allowing coolant directly into the cylinder. Second: The head gasket fails at an oil return port allowing coolant into the engines oil return system.

Step 6 - If a cylinder head has a crack due to overheating it can allow coolant into various internal engine parts. Visit - Engine overheat. To check for this condition the cylinder head must be removed for inspection.

Step 7 - Lastly, coolant is present in the engine block. If this block becomes cracked it can allow coolant to enter the oil return 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. Visit - Cooling system. The engine cannot run with coolant in the oil system, catastrophic failure will occur. Do not run an engine once is 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.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-14)