CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Transmission Fluid in Oil

I recently took my wife’s care into my mechanic because it had a serious knocking problem. My mechanic called and asked who did the oil change, because there is transmission fluid in the oil. He had seen it before with a quick lube place (just like we had taken it too). Would this have any effect on the motor if driven for quite a while this way?

There should be no problem…Transmission fluid is basically high detergent 5 or 10 weight mineral oil. It should not have caused any clunking or other problems, especially if driven only a mile or two…Now on a hot summer day at interstate speeds, engine damage could occur.

What kind of car are we talking about here? How many miles?

Sorry, I misread your “Quite a few miles” statement…That’s a different story…These stories seldom have happy endings…

I am not an expert on this problem but it sure sounds like, yes, it does, it makes it start knocking, heh, heh. Hope you get better answers from our best mechanics.

You are about to learn that the people here view taking your car to a quick lube place to be an act of self-destruction – or car destruction, if you prefer. The employees are not highly paid nor motivated, and as you have seen, they do make mistakes.

Also, if you don’t change it yourself, no matter who does, when you get the car back, open the hood, and check both the transmission level and condition, assuming it is automatic, and the engine oil level and condition. Learn what things under the hood look like so you can spot any problem or error.

Does your mechanic know which dipstick goes to the engine and which dipstick goes to the transmission?

Maybe he is the one that has them confused. Especially if he tells you the transmission is full of motor oil! (your car will not go few far at all with motor oil in the tranny).

Quick-lube joints with bulk oil dispensers, they have 6 different delivery hoses hanging down, it’s easy for a “Grease Monkey” to grab the wrong one…

Oh yes he does. He is very qualified. The problem is that my wife took it in and was driving the car during the summer on a long trip. When she returned from the trip the knocking was pretty bad. Now is sounds like perhaps the cam followers/cylinder heads are damaged, but who knows how much until they tear into it.

Is there any retribution with the quick lube place for damages or are we just SOL?

In civil court you don’t have to prove beyond a reasonable doubt that the garage was at fault. You just have to be more convincing in front of the judge–than the garage is. But you may not even have to go to court. I think fastlube places settle out of court quite frequently.

Are you a real regular customer at your regular garage? If so, you might be able to sweet talk them into signing an affidavit that it was ATF in the engine. All you might have to do then, probably, would be to just show the manager of the fast lube place the affidavit, to get them to pay for engine repair/replacement. Good luck and post back.

Thank for you input. I will talk to my mechanic and check back. Sounds like good advice.

After you make them change out the fluids to be exactly correct, check the oil again at several intervals for signs of transmission fluid.
If they messed up and put fluids in wrong, you’ll see no more fluid mix after they get it right.

But, if you see trans fluid again , you may have a bigger problem. Such as corrosion in the coolant heat exchanger at the radiator/trans cooler. ( we say transmission cooler, but it also serves to heat the transmission fluid when starting out. )

If it’s an automatic there should be trans cooler lines that go to the radiator for heat exchange. The coolant radiator and the transmission ‘cooler’ appear to be one unit and are built together as you see, yet are independent reservoirs abutting each other for heat exchange.
Internal corrosion can allow the fluids to mix and radiator replacement would be needed.

My opinion is that the engine is damaged goods, pure and simple.
Transmission fluid has different lubrication characteristics as compared to motor oil.

I think you are SOL…Too much time has passed…Had you saved a SAMPLE the fluid in the crankcase it could have been analyzed at an oil lab to PROVE it was ATF…THEN you MIGHT have been able to press a claim against the quick-lube joint. Without PROOF, it’s just he said / she said…Have you called the Quick-Lube place?? They have insurance for these claims and they MIGHT offer some help. It’s certainly worth a phone call…

I think you will find most of the damage will be found in the main and rod bearings…The valve gear should have survived…