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Messed up (again)

Well, I accidentally put 1 1/2 cups of 5w 30 motor oil in my 2002 Grand Prix auto. transmission. The trans. fluid and the oil were both in the same make and same color containers. The car has 97500 miles on it. So, anyway, after jumping up and down a bit, I drove it about 2miles to the garage where they flushed it good and changed the filter and fluid. I drove it the next day (it was Xmas) to my brothers about 150 miles away and it did fine. I took it back in the day after Xmas for the mechanic to look at, and it seemed just fine. Does anyone have any idea that I may have done some damage over the long term or not ? There’s no slipping although I drove it today about 70 miles in a combination of stop and go and hiwy conditions, so it got pretty hot, and it was shifting just a little hard, but overall ran fine. Hopefully I’m just paranoid. What do you all think?

No way to know for sure from here but I very much doubt any harm was done.

It would have been preferable if you could have simply it out from the pan before driving it. Then you’d have not had much of any problem at all, other than the inconvenience. But I doubt you did any seriouis damage in any event. The worse probably is that you may need to rebuild the transmission a little sooner than if this didn’t occur.

Automatic transmssion fluid is just straight 10 weight oil with the proper additives.

That small amount engine oil you added to the transmission fluid would have done no harm.

But since you had the tranny fluid exchanged, let’s see if the tranny goes another 100,000 miles?


I agree with everyone that you’ve done no damage. You did the correct thing in getting it flushed out immediately, which is always the proper protocol with a problem like this. If you were going to have a problem, you’d have known it during your 300 mile round trip to and from your brothers.

Happy motoring.

" . . . I drove it about 2miles to the garage where they flushed it good and changed the filter and fluid. "

John, was it “flushed” manually by removing the transmission pan, emptying the fluid, and refilling it or was it hooked up to a machine that did the flushing (fluid exchanging) ?

How’d they do it ?


They used a machine to flush it out. They said it gets 90-95% of the fluid out. All except what’s in the torque converter.

If they used a transmission fluid exchange machine all the transmission fluid was replaced. Watch this video.


I wouldn’t think the difference in the fluids would make that much difference as long as you flushed it asap. I have 227k on mine.