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Transmission fluid mixed in with engine oil

I accidentally put about 1/2 cup of automatic transmission fluid in the engine oil reservoir in my 1995 Mercury Grand Marquis. What will happen? I have driven about 20 miles to get home tonight, but plan to go to Superlube in the morning. Will my engine be okay?

Most likely no damage.

No problem at all-- a lot of people will add transmission fluid to the oil from time to time to clean out the engine. If you had added a lot, it probably would have been a good idea to change the oil sooner rather than later, but if it’s only half a cup (by which you mean 4oz, right?) it shouldn’t be a problem at all.

other than cleaning out the oilways… and the rings… I’d not expect any damage. if it’s close to oil change time, you may as well do an oil change. Too much cleaning and your rings and valves might start leaking leaking a tal more.

This won’t do any harm at all. In fact, back in the '50s & '60s, before oil detergents were as good as they are now, some people used to add 1 qt. of trans fluid to their motor oil once a year just prior to an oil change, in order to clean out their engine.

But, just for an extra measure of prudence, why don’t you have your oil changed in a week or so? In the meantime, just drive normally, and don’t panic over this little incident.

ADDENDUM: Superlube??

If that is a quick oil change place, you have a much higher probability of having your engine (and transmission, and brake hydraulic system, and differential, and power steering) damaged by them than by your act of adding some ATF to the motor oil.

On a regular basis, people report on this site that their cars have sustained major damage from the rapid pace and the inexperience of the poorly trained employees at quick oil change places. We have heard about ATF or windshield washer fluid being added to the brake master cylinder, transmissions being drained instead of the crankcase (leading to a grossly overfilled engine and a “dry” transmission), improperly tightened oil filters, and other examples of mistakes that have caused major damage to cars.

As Joseph Meehan, a veteran of this site says, “Don’t go to a quick oil change place–even for directions!”.

I don’t know your car,It has a “engine oil resivoir”, you don’t add engine oil through a removable cap on one of the valve covers? Your description makes me think you put the ATF somewhere other than the engine. I guess the engines oil pan could be considered to be a “engine oil resivoir”.

The transmission fluid mixed with the oil should not be any problem for short distances.  

However I would not say the same for any place called "Superlube"  It sounds like another quick lube place and they all are well known for errors and selling services that are not needed or desirable.