Why is there a milky brown oil layer in the coollant reservoir of my Mazda MPV?

There are many ways that can happen. Bottom line it was oil from the engine mixing with the coolant. And it was a cheap fix. Not a head gasket.

... Or you have a weak or blown head gasket.

Well tennisshoes, the only thing we had recently done was an oil change and check at Jiffy Lube, before that absolutely no problem. The weirdest thing is that when we start the car it purrs like a kitten it does not sound like anything is wrong, we also did a computer check at the auto shop everything seems normal. We flushed it twice now and it was clean but now there is more oil. What other symptoms are there for a blown head gasket, will the car even run?

Has anyone ever used Steel Seal? Should we or not try this?

https://www.steelseal.com/?gclid=CIXl-r2Uj8ACFQwV7AodnXkAGg

Ouch! That sounds serious! There is no white smoke or engine miss, the oil is not reddish so it is not transmission oil. The engine oil does not go down at all. I guess you are right, a exploratory tear down might be it. That will probably be very expensive :( Oh man!

I am not sure about mileage, I so want to keep it it is such an awesome vehicle. Very good on gas too. We will have to look at our options, my husband is currently working in Jacksonville, FL and the MPV is our only car, at the moment. Thank you so much for your advise.

So it turned out that the oil changing place actually added some oil to the coolant reservoir! After flushing the system 3 times there is no more oil at all in the coolant. Thank heavens!

He he, Mark you are funny! Anyway it is a long story and our mechanic got to the bottom of it all after gasket tests and all sorts of checks, when he heard where the car went for the oil change he knew immediately. He said the same thing happened to another client of his. I believe the company does radiator flushes and they probably need more business! Anyway we are just relieved that there is nothing wrong and we caught it in time, we flushed the system and the car is running great, mystery solved. I believe my husband will still pay a visit to them to inform the manager about this but we will not charge them as it did not cost much to fix. Silly negligent people! :)

I would incurage you fire if a letter to there corporate office. You were able to get to the bottom of the problem by determination and preserving. You knew something didn't add up. Think of the retiree that lives on a limited income and is going to give up something else to pay for a $99.00 radiator flush that they don't need. Old farts like me are dependent on our cars and in many cases it's our freedom.

Yes Mark, we will do that. I agree the bosses should know what is happening. Thanks for that advice.

I am an ex mechanic from NJ and I am having the same issue with milky coolant in the overflow tank, I thought it was the head gasket at first as most would but no other signs. After checking the cooling system I found that the oil cooler just above the filter had gone bad, coolant and oil were mixing. I talked to an mechanic at Mazda and he told me that this was common with MPV and some other models.

I know this is really old and you all are probably never on here anymore. But my 08 is having this exact same problem. No white smoke runs and puts like a kitten, pulled the oil plug and no antifreeze in it. But my resvrior is full of oil and is now in a radiator. (I do my own oil changes, and my husband and I already replaced the cooling unit in april (never will get a part from rockauto again).