Transmission Fluid to flush an engine

First off, i know the topic of engine oil flushes and additives has been brought up in many different treads, and after reviewing those I agree that they are bad and do not want to start another discussion about them. My question is about the alternatives to using one of those flush products. From my research done on the forums, I have found that the general consensus is the best way to clean out an engine is to change the oil much more often than the regular interval such as every 500 miles for 2000 miles. I was talking to someone a few days ago about all this and they said that another good method was to drain a quart of oil from the engine, replace that quart of oil with a quart of transmission fluid, run the engine for about half an hour and then drain the oil.

Has anyone ever used this method to flush an engine and if so how would you rate its effectiveness and safeness? The argument that the person i talked to made was that transmission fluid contains many detergents and cleaning agents that are effective at removing deposits that build up in the oil passageways. If anyone could offer some more information on this i would greatly appreciate it. Thanks!!!

I have heard of this suggestion before. I expect it will be safe for the engine, but I am not sure of its effectiveness.

I have also heard of adding a quart of kerosene or a quart of diesel fuel instead, when the engine is cold. These methods are very effective at cleaning an engine, but you must NOT put the engine under load. Allow it to idle in neutral only for 1 minute then let it sit for an hour, before changing the oil.

I used the diesel method once and it really cleaned things up Huge amounts of junk came out with the old oil, and the new oil stayed clean for a long time. However, I would not want to risk possible bearing damage by doing it again.

IMHO unless the engine is running poorly due to deposits, just change the oil reasonably frequently.

i dunno... tranny fluid doesn't have the lubricating properties of engine oil, and mixing them could do damage... but like MagicRat said, most flush techniques are meant for only engines NOT underload.
And on the topic of diesel... i've heard (and know from experience) that it's a great way of cleaning you valves and injectors...lol
it sounds wierd, but if you add a quart of diesl fuel to an almost full tank of gas, and run it down, your injectors and valves will have the 'grunge' build up removed.... keep in mind though... you will have less performance in you car (so don't go racing), and your car WILL smoke more than usual.

i dunno... tranny fluid doesn't have the lubricating properties of engine oil, and mixing them could do damage... but like MagicRat said, most flush techniques are meant for only engines NOT underload.


I think the reason behind the tranny fluid is that transmission fluid has a lot of detergents integrated into the fluid.

I have also heard the kerosene method too and I have no idea what is in a bottle of engine flush but I imagine it is some sort of spirit neither of which have good lubricating properties.

None of these should be used with the engine under load.

Back to diesel fuel...............You say you know from experience that this works? Interesting.I have heard this but I was always doubtful. Do you have any fear of ruining the cats or o2 sensors?

Back to diesel fuel...............You say you know from experience that this works? Interesting.I have heard this but I was always doubtful. Do you have any fear of ruining the cats or o2 sensors?

Well, i've tried it on two engines... one being my carb'ed '72 GM truck... of course there are no O2 sensors or cats on it...
The other is my '88 Beretta, and i have no cat on it... cuz i put on a performace exhaust.... but the O2 sensors don't seem to mind if you are easy on the amount of diesel you put into the tank...
But as i suggested, go easy on the car if you do this... no racing...lol

It is a fairly old trick. On your next oil change, replace one of the quarts of motor oil with a quart of ATF. ATF is really high detergent and will clean out your engine quite nicely. Run your engine with that in it for 1000 km or so and then change it again, back to all motor oil. I have done this and it has always given me good results and no harm has come to any of my engines. I learned this from one of my old shop teachers.

Back to diesel fuel...............You say you know from experience that this works? Interesting.I have heard this but I was always doubtful. Do you have any fear of ruining the cats or o2 sensors?

If you go to the parts store and buy a product called "motor flush" in a silver cylindrical can, its basically diesel fuel with some of the volatility removed so it can be shelved.

I've done the diesel flush and it works pretty well. The transmission fluid is somewhat of a misconceived (but somewhat effective) method. It started way back with someone realizing that trannys were always spotlessly clean when they were torn apart. They assumed that the tranny fluid did some cleaning while in there and put it in their engine to flush it. The reason trannys are so clean is because they don't have blowby, carbon, and moisture build up like an engine. They have clutch friction material which gets filtered out, but its a sealed system in which no combustion takes place. There is nothing to make a tranny dirty in the first place, so people assumed that the fluid scrubbed it clean.

Transmission fluid does tend to flush out an engine, but I think its mostly because its the equivalent of 20wt. It flows in the nooks and crannys easier.

Diesel works pretty well, but like everyone else said, DON'T rev, drive, or even touch the throttle while its in there, and after the flush I would suggest driving very gently on the new oil until the volatiles have evaporated out. I might also suggest another oil change very shortly since there will be remnants of the diesel in there that don't evaporate.

You may be better off with Marvel Mystery Oil...

The reason trannys are so clean is because they don't have blowby, carbon, and moisture build up like an engine. They have clutch friction material which gets filtered out, but its a sealed system in which no combustion takes place. There is nothing to make a tranny dirty in the first place, so people assumed that the fluid scrubbed it clean.

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I have always beleived what you said to be true in that the reason transmission fluid is always clean is because it does not get contaminated due to combustion but one thing I do not understand is why does Transmission fluid wear out? Shouldn't it last forever???

I have always heard that if one could filter engine oil effectively the fluid could last significantly longer than 5000K. In fact I have heard of some people replacing their filters and not the oil. (although I would never dream of this).

DO what Curtis Recomends...the motor flush.

I took his advice, and it worked great. My tbird is a 4.6 v8, with 130k miles...and everytime i changed the oil, no joke 1500 miles later it would be BLACK. NOW, it's 2500 miles, and it looks almost new. Infact, tomorrow i'm gonna change my oil cause i'm gonna clean my engine w/degreaser and a hose....just to make you i don't have any chemicals in my engine.

I have always beleived what you said to be true in that the reason transmission fluid is always clean is because it does not get contaminated due to combustion but one thing I do not understand is why does Transmission fluid wear out? Shouldn't it last forever???

Yes, but eventually the additives start breaking down just like with any oil. It also suffers from heat spikes which scorch the fluid. The big factor (I was told) was that the carbon material in the clutches gets dissolved. While clutch material usually gets picked up by the filter, the carbon compounds actually dissolve in the oil and begin to change its properties.

I have always heard that if one could filter engine oil effectively the fluid could last significantly longer than 5000K. In fact I have heard of some people replacing their filters and not the oil. (although I would never dream of this).

There are actually filtration products on the market that claim you never have to change the oil. You do have to change the filters, but the oil itself doesn't break down. Its additives do get consumed and I don't know how they get around that.