hi I have 99 mustang and I found oil in my coolant resvoir, so drained and replaced the coolant back in April, so last week I take a look under it hood like I always do but last week I see oil again I know I don't have a a blown head gasket becuase my car never over heated and my taipipe smoke is clear and my heat/AC doesn't smell like burnt coolant. Can somebody tell what could it be? Or what to do
I could suggest only blown head gasket, regardless of the condition of the rest of the car. I have been there with many, many people and cars I have diagnosed correctly. Almost 40 years on this.
You could make sure it isn't transmission fluid swapping over somewhere, but that doesn't really happen.
A previous mixture of coolants and your change if not completely flushed, also makes brown, muddy deposits.
Heat/AC only smells like sweet & foggy or burnt coolant when the heater core is gone, or leaking.
Also, always look the opposite way, and see what's inside the oil!
oil or muddy? cuz mine is muddy and i finded out that the previous owner put it a special can to seal the radiator cuz its cracked but that only last a few months. also it smelled burn and something smoke was coming out of my hood. i already put some water on it cuz my car was almost in the middle of the hot range. and now is not that fast. oh and that liquid makes your antifreeze muddy. i need to fix my radiator.
You can get oil in the water in only a few places - head gasket, intake gasket, or front cover. With a bad intake or front cover gasket you usually get water in the oil, though.
Take a sample of your coolant down to a local repair shop and have it tested for by products of combustion. If that test is neg, then it's most likely not the head gasket.
i use Royal Purple and It Comes out Clean when i do an Oil Change, like oil will accumulate in the coolant resvoir and once every year ususlaly during the winter, i had the car checked at mieneke and they told me my car was fine
i would probably suggest a full cooling system flush at this point...and if the coolant starts looking muddy again, then you know for sure you have a leak somewhere.
im surprised mieneke didnt try to sell you a coolant flush lol.
Oil in my coolant resevoir, 1999 Mustang V6 
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