This was possed to go with the synthetic oil thread,
but the powers that be said I had to use a subject line,
so it made a new thread out of it. Oh well, I'm sure
I'll get jumped on, but it won't be the first time.

I forgot to mention, this was for motor vehicle engines,
not lawn equipment.

I've heard that too. Never tried it myself. Since I always have MMO around for use in my fuel, I just stick to it.

I heard this many times, but it is untrue.
ATF and hydraulic fluids do not have any detergents.
I copied this from Havoline Oil.
ATF does not contain detergent chemistry. ATF does contain dispersants, which have properties similar to detergents. But ATF is not formulated to withstand the combustion environment inside the engine. Havoline recommends that you keep the fluids where they belong: motor oil in the crankcase, and automatic transmission fluid in the transmission.
And you can take that to the bank.

If you want to really clean out your engine just drain 3/4 of the oil and replace with solvent or gasoline and run wide open for 30 minutes. Guaranteed it will loosen all sorts of crud. If a few oil lines get plugged up - no problem. Just drain and repeat the process till it's clear. After it's shiny inside and the crankcase drains clean it may sound a bit rattly. No problem. Just run a 50/50 mix of engine honey and 50w oil.

Don't buy the Engine Wash BS unless you wish to prematurely replace Lifters , Rockers and eventually Bottom End Bearing ...Sheeesh !

A friend poured 3 quarts of tranny fluid into his engine, before he discovered his mistake! He drove about 30 miles, then drained it out, and installed the correct oil. Said it didn't seem to hurt it.

In the garage I worked at, whenever you got into a really
dirty job, (like replacing the rear brakes on a big truck
that the seal leaked and the diff. gear oil mixed with
the brake dust), we would massage ATF into our hands before
washing with the hand cleaners, and it seemed to get more
of that crud out of our pores. Back then the brake dust was
asbestos, but I'm not dead yet, (I don't think).

Old Mechanics use to recommend adding a few (3-5 ounces) of Dextron to the engine oil when noisy hydraulic lifters became came an issue , there is a degree of solvency within Dextron hence the dirty lifter issues quite often were cleaned. However adding a quart or two or even worse Gasoline or as I have hear numerous times Varsol is just Stupid and asking for trouble . Kerosine perhaps in moderation . Even then a few miles and then dump the oil and refresh c/w new filter .

I'd like to look behind the wall and see the tank that supplies MMO to it's filler. I'd laugh if it was ATF.

I spent 27 years at the brewery and we'd put on an 1800 barrel tank of our namebrand product and run a few thousand cases of this and a few thousand of that, changing labels and cardboard and using the same tank.

"I spent 27 years at the brewery and we'd put on an 1800 barrel tank of our namebrand product and run a few thousand cases of this and a few thousand of that, changing labels and cardboard and using the same tank."

I'm not surprised. Likely very common with breweries that produce for their house labels as well as other beer companies. The label and the image are what most people are buying with beer, wine and hard liquor. Blind tasting and identification tests are usually revealing.

"If you want to really clean out your engine just drain 3/4 of the oil and replace with solvent or gasoline and run wide open for 30 minutes. Guaranteed it will loosen all sorts of crud. If a few oil lines get plugged up - no problem. Just drain and repeat the process till it's clear. After it's shiny inside and the crankcase drains clean it may sound a bit rattly. No problem. Just run a 50/50 mix of engine honey and 50w oil." That's just too good Roadbike! I could never bring myself to want to clean old deposits out of a crankcase. Not good for what (ales;) ya...