recently, I checked under the hood as a result of suspicious odor…lifted cap on overflow to find tank filed to brim with oil; radiator is not contaminated. All fluids seem right level and appearance. No sign of leakage. ANY IDEAS???
If you have an automatic transmission check the fluid level in it. The transmission cooler is integral with the radiator, and a leaking transmission cooler can contaminate the cooling system with transmission fluid.
Wait! If the radiator is not contaminated, how did the oil get into the overflow? Is it possible that someone poured oil into the cooling system overflow instead of into the engine? Otherwise, I fail to see how it got there without traveling through the radiator.
How do you know that there is no oil in the radiator? The only way to check that is to drain your radiator and look for contamination, but even then you cant be sure that no oil was ever in your radiator.
Do you have any suspicion that someone could have poured oil in your overflowtank?
Has it recently been in for an oil change?
If you think a garage is responsible for this, take it back.
If not, and its still a possibility that someone poured oil in your system I would drain, flush and refill your cooling system and then keep a close watch on both engine and transmission oil level as well as the condition of your coolant.
And dont let anyone you dont trust under your hood again 