Engine drained refilled with ATF

My engine oil was drained,filter left on (I think)and refilled with ATF.I drove 140km before noticing.Any idea on the extent of the damage if any.
The truck seems to work better than before,oil pressure if about the same as before.
I am trying to get the dealer that did this to give me a written warranty in case something does go wrong.
The truck is a 04 Silverado 6.0litre with 250000km.

Get. It. Out. Naow.

Transmission fluid is just straight 10 weight oil with a higher detergent content.

Change the oil and filter and all should be good.


Drain it now including the filter…I used to do this on older engines where I had sticky lifters…but I would just drain a quart out and add a quart of ATF…no damage would be done this way…would drive it for about 100-200 miles then do an oil change. ATF is a 10 weight oil…too thin for you vehicle…and may lack proper lubrication qualities for an engine but does clean better than regular oil…If you had no engine noise etc, probably little if any damage done and if your oil pressure was in specs. You probably cleaned a lot more gunk out but get it changed ASAP ! I bet that ATF will come out black just after 140km. ( about 85 miles ). You do not want an aggressive flush as it can block the pick-up screen with chunks of debris on the pump what pure ATF can do.

I know they sell a motor flush where you add a quart and run the engine at idle for 5 or 10 minutes,never trusted that stuff as it came out of the can like water and would thin the oil too much. Smelled like kerosine. I can;t believe a dealer could make such a big mistake…Sounds more like a quickie lube place where they have teenagers changing oil. I always do my own oil changes so I know what I am putting into my engine.

How did you figure out that you had ATF instead of oil?

Was this really a dealer or was it a quick-lube shop?

I doubt it’s anything to worry about. Just get an oil change and filter as soon as you can.

You may have done more good than harm, the engine is probably cleaner now.


Interestingly, I just went on the internet to try to find out the viscosity of various ATF fluids, along with other differences in viscosity modifiers, additives, etc., and was totally unable to. I even found that some manufacturers specify a “special low viscosity ATF”, but was unable to find out what viscosity that actually was. You’d think it was a classified national security secret… on second thought, THOSE I can find!

I’m comfortable with no damage having been done, since the pressure never wavered and ATF is, in the final analysis, a lubricating hydraulic fluid not totally unlike motor oil, and capable of keeping a pressurized fluid barrier where it’s needed, but it sure would be nice to be able to reference some technical information.

Anybody got any technical links?

The DEALER did this?!? Go ahead and do a proper oil change. The ATF probably cleaned out any carbon build-up and gum in the oil passages. But, get the right oil in there ASAP.

I’d probably change the oil and filter. Drive for 20-30 miles. And do it again. I doubt there’ll be any permanent damage. But it would be a good idea if you can to get the perps to admit in writing with appropriate signatures what it was exactly that happened and when.

I too will vote for the goodness of ATF. It’s better than most of the stuff that gets added to your engine by mistake. A lot better.

“It’s better than most of the stuff”

Like slick 50, which also gets added to your engine “by mistake” . . . ?


At least now, you are not ready for another change for at least 60k miles .

ATF is typically a thin synthetic oil with an additive package lacking the things that deal with the byproducts of combustion.
140km isn’t long enough to foul what is essentially a non-detergent oil.
Shaft seals won’t be damaged because it’s chemically so close to motor oil.
Bearings will be fine because ATF is formulated handle the high pressure and resist scuffing of meshing gears.

Thanks for the input it has helped to calm me.
It was done at a GM dealership and I an waiting for a call from the service manager about possible warranty.

“How did you figure out that you had ATF instead of oil?”

Yes, I’d also like to know. Pull the dipstick and “see red”?

Road bicycle gearheads sometimes use ATF in their own personal chain lube formulations. Usualy something like 1/3 ATF, 2/3 OMS. I’ve tried that idea for mt. biking, but it is a little too sticky for off road riding conditions we get here in the dry, dusty west. The dust sticks to the chain too much.

ATF is oil but it needs to come out of there and make sure to replace the filter. There are thinner oils on the market and people use them everyday in their vehicles. I don’t see a problem since you only drove it 140km.

@GeorgeSanJose, what is OMS?

The thing that would concern me most would be the friction modifiers in ATF. Some modifiers reduce friction while some actually increase it. Both can be in one ATF fluid depending on the clutch formulation. I don’t know if this would be a problem in a engine but I would not want it between my bearings and crankshaft.

The friction modifiers are for the clutches in the transmission. There are no clutches in an engine.

The friction modifiers don’t damage the bearings in the transmission. So how are they able to damage the bearings in the engine?