# Oil In the Coolant



## Abaaba (Jan 5, 2017)

As the title says, today I found traces of oil in the coolant expansion tank whilst doing my normal routine checks. I think I caught it early (if that makes a difference)

I have searched through the forum and cant seem to find anything, where do I start? what other checks to do? will a through flush and new coolant make any difference?

The coolant still got its color but you can see oil forming around the expansion tank

any help/advice is really appreciated.














Pictures were taken night time so not clear enough.
Thanks


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## Robby (Mar 1, 2013)

Most likely cause is a leaking trans cooler (part within radiator).

No static test for this....I'd exchange the radiator pronto before the leak gets worse and allows coolant under pressure (at engine shut off) to push into the trans...........Actually, I think a trans flush would be wise in conjunction.

Rob


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## Abaaba (Jan 5, 2017)

Robby said:


> Most likely cause is a leaking trans cooler (part within radiator).
> 
> No static test for this....I'd exchange the radiator pronto before the leak gets worse and allows coolant under pressure (at engine shut off) to push into the trans...........Actually, I think a trans flush would be wise in conjunction.
> 
> Rob


That makes sense.

I recently done (8 days ago) trans oil change but I made sure I didn't overfill, then all of the sudden this problem started. Is it possible that I may have overfilled it and this caused the issue?

Thanks


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## Robby (Mar 1, 2013)

Abaaba said:


> That makes sense.
> 
> I recently done (8 days ago) trans oil change but I made sure I didn't overfill, then all of the sudden this problem started. Is it possible that I may have overfilled it and this caused the issue?
> 
> Thanks


Overfill would not cause a failure.....I assume the cooler line to radiator attachment points were not disturbed, but, if they were, overtightening could fracture the cooler.
Otherwise, I'm stuck with unlucky coincidence.

Rob


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## jblackburn (Apr 14, 2012)

Robby said:


> Most likely cause is a leaking trans cooler (part within radiator).
> 
> No static test for this....I'd exchange the radiator pronto before the leak gets worse and allows coolant under pressure (at engine shut off) to push into the trans...........Actually, I think a trans flush would be wise in conjunction.
> 
> Rob


Trans cooler is a separate, standalone cooler - at least on US model Cruzens.

The oil cooler is a shared coolant/oil heat exchanger at the oil filter housing. THAT one might be a culprit...it has happened before.


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## Abaaba (Jan 5, 2017)

I think I may have found the culprit, one the lines going into the radiator has a leak. does the radiator need changing or it is just changing the lines?


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## Robby (Mar 1, 2013)

Your photo is where the trans cooler lines enter/exit the radiator.....a common external leak point, however I am referencing the cooler that is in the radiator.....what the lines are attaching to.
When it develops a leak it pushes trans fluid into the coolant......so, I still am of the mindset a radiator replacement (and likely cooler lines or line 'O' rings) may be in order.

Rob


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## Abaaba (Jan 5, 2017)

Robby said:


> Your photo is where the trans cooler lines enter/exit the radiator.....a common external leak point, however I am referencing the cooler that is in the radiator.....what the lines are attaching to.
> When it develops a leak it pushes trans fluid into the coolant......so, I still am of the mindset a radiator replacement (and likely cooler lines or line 'O' rings) may be in order.
> 
> Rob


Thanks for that mate. I am gana have to replace the radiator and cooler lines, flash the system and hope that solves it.

Can I remove the radiator without removing the A/C condenser (dont really want to touch it) front bumper and everything else in front of it? anyone wrote ho to tutorial?

Cant believe GM spare parts want £350 for the radiator alone!!


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## Robby (Mar 1, 2013)

Radiator can be removed independent of the A/C......leave the fan attached and transfer to new unit prior to re-install.
You should be able to do it from the engine side with little difficulty, assuming you have a decent tool box. 

Re- use the spring hose clamps.....gear type can crack the necks.

Rob


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## blackbird (Nov 6, 2017)

A leaking internal trans cooler inside the radiator could allow transmission fluid into the coolant. Since you're in the UK and I'm not sure which powertrain you have and if it's applicable, if your car has an oil-to-coolant heat exchanger those can also leak internally and allow oil and coolant to mix.

A cracked turbocharger CHRA (center housing rotating assembly) for a water and oil cooled turbo could theoretically allow coolant into the engine oil, but since the housing isn't pressurized with oil outside the bearing surfaces (and in fact would leak oil past the dynamic seals into the compressor and turbine wheels if the CHRA were pressurized with oil), you wouldn't see oil getting into the coolant from a turbo problem.

Other most common source for oil getting into coolant system would be a head gasket leak, but with modern multi-layer steel head gaskets they usually don't weep oil to coolant passages and vice versa but instead normally fail catastrophically. It would still be a possible source if you have a trans cooler in the radiator or oil-to-coolant heat exchanger you've ruled out.

Another test you could do is to send a sample of the engine oil in to an independent testing lab for a used oil analysis. In the US there's companies like Blackstone Labs and others that can do an analysis of the motor oil and this will often show if even tiny amounts of coolant is getting into the engine oil well before it becomes a milky sludge. I'm not sure if any of the testing labs might be able to take a sample of the coolant and identify what type of oil (ATF, motor oil, etc.) is present.


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