Accidentally put coolant stop leak in transmission fluid

So I had a coolant leak not a major one, I was told by my mechanic that I could use stop leak. Well I thought I had put it into the radiator but while driving down the road my car stopped working I pulled off and popped my hood and that’s when I realized I put it into the transmission fluid! The caps look so similar and the dirt had completely blacked out where it said transmission… turned off engine and called tow truck… but how badly did I mess up my car? Is this fixable?

Ugh. Probably “fixable” with a new transmission…This is not good.


I am very aware that it’s not good :woman_facepalming:t2: I was hoping maybe it could be flushed out… the way GMC has designed the placement and and symbols for the two caps made it easy to mistaken one for the other… but I do know I should have been far more careful

Are you sure you put it in the transmission?
I’ve NEVER seen a transmission fill point that would be easy enough to add fluid without a funnel, or that has a cap that could be confused with coolant.

Picture please.


So the cap was dirty and the only thing that I saw was the part of the symbol and the dex which I since the second part had been worn out I thought it said dex cool which Is what I put in for coolant … the picture is the transmission fluid cap after I scrubbed off all the gunk that was on it …

This is the symbol I mistaken it for from my over flow cover

I do want to clarify that the only thing visible before I scrubbed off was the dex- and part of the symbol

Have the transmission fluid flushed, and cross your fingers.



I was definitely planning on doing that but first wanted to get some options on if that would even do anything or if this was definitely a fatal error

Are you sure that’s not the power steering cap? Is there a short dipstick attached to it?



So there is a cover that is over the engine when I was shown where the radiator cap was the first and only time it was a few years ago and that cover was already off… so I didn’t realize that at the time and I added a picture of what that cap looks like … being dirty and just showing the symbol and the word dex do you understand how I confused them :woman_shrugging: I never usually put anything in my car myself and after this will never again!

Here is the location of the power steering cap.

There is but it definitely says transmission fluid… I had figured that I had to have done something wrong so I cleaned off the cap really well and that’s when I realized what I did

And here is the proper power steering fluid. Dexron VI, just like it says on the cap in your picture.

Right which just makes things even more confusing… but when it started acting up it was definitely transmission related kinda felt similar to a spark plug issue …

So is that cap for the PS or for the transmission?

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So there is a cover over that part of the engine… and the place I put it into was the other side and not under that covered part

@NYBo it definitely is the transmission fluid cap although they are all very similar and that’s the part I hadn’t realized I also had forgotten that the cover was not on when they showed me where all the caps were located… and it through me off

I would say you are now in the market for another transmission.

I am sorry to say this but I would start shopping for a new transmission.