ATF in my oil change!

I was changing my oil in my 04 4Runner and found ATF mixed in. I checked my atf level and it was low. I began adding new oil to the engine and after about 4 quarts I ran the engine. Turned it off and checked the level and it was way above the full indicator. How is ATF getting into my engine!?

How do you know it is ATF that is getting into your engine? Are you checking the correct dipstick?

I’m not a mechanic but I do my own general vehicle maintenance. This was just a routine oil and filter change. The oil had a reddish tint and was thinner than it should’ve been, and I could smell the atf in it. Also my transmission fluid was low. So I’m certain that it’s transmission fluid. I just don’t know how it could get into my engine.

I don’t know of anyplace where the ATF and oil share space, but there is an ATF cooler in the radiator. How is your coolant looking?

I do know of two cases where a professional mechanic drained the transmission and then overfilled the engine. Now by professional mechanic, I mean they were being paid to do mechanics work.

Edit: BTW one was a Toyota Corolla.

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Only thing I can think of, You added transmission fluid to your engine instead of motor oil.
Bottles of oil mis-labeled, or you didn’t look close enough at the bottle.

Don’t get upset but I tend to think this is operator error and do not feel bad about making a mistake. There’s not a highly competent mechanic on the face of the Earth who has not made a error or two along the way. And one or two of those errors cough makes you wonder WTH they were thinking…

You might want to check if the vehicle has a bad modulator valve.


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Could it be possible that the transmission cooler in the radiator is cracked, mixing with the coolant and then getting through a blown head gasket?

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Thank you for the link. It was very informative. I will check this promptly.

I definitely considered the possibility of grabbing a quart of atf by mistake last oil change. I only wonder if there’s something else going on after today’s oil change because the dipstick is reading much more oil than I put it. I bought a 5 quart container. So there’s no confusion with an accidental pour of atf.

I think you drained the transmission oil pan instead of the engine oil and then added 4 qts of oil to an already full engine.

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This seems to be impossible.

The oil capacity is 5.5 quarts, I can’t imagine how more than a quart and a half of transmission fluid could transfer from the transmission to the engine in less than a minute. How many quarts low is the transmission?

Power steering fluid/ATF can leak through the power steering vacuum switch into the intake manifold but that would be ounces, not quarts.

Are there remote filters or coolers for both oil and transmission on this vehicle?
Thinking they could be plumbed wrong.

Here’s an idea.

Since both the engine oil and possibly transmission fluid seem to be either mixed and/or low… have the vehicle towed to a shop and have both fluids changed/topped off. Especially the engine oil; I don’t think ATF works well as an engine lubricant.

That way you can start fresh and see if you really have an issue. Or if it was just “user error”. Either way, I wouldn’t want much ATF in my engine oil, personally.

On more than one occasion I found that transmission fluid was being pulled out of the modulator valve and accumulated in a junction of vacuum hoses jointly connected to the manifold and the PCV valve was among the devices connected. ATF drawn up, over the intake would drain through the PCV valve when the engine was shut off. On repeated wide open throttle operation the ATF would cause heavy smoking. As best I can recall it was GM pickups that had that problem and certainly not Toyotas but the spaghetti under the hoods of some cars over the years has been very confusing even with a diagram.

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I replaced both oil and atf. Will go from there. Appreciate everyone’s help and input.

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I have a hard time seeing a modulator valve on a 2004 4 Runner. I thought modulator valves went the way of the Pterodactyls who were squabbling over them.

Since both have been changed I think things will be fine. A small amount of ATF or motor oil mixed should not hurt anything.