Engine Full of ATF- How Bad?

Story time- I let a shop flush the trans in my truck (2001 Silverado with the 8.1L gas/Allison combo) and they apparently grabbed the oil cooler lines instead of the trans cooler lines and "flushed" the engine with ATF without noticing.  I got the truck back, drove it on a couple errands, noticed the oil pressure dropping at higher revs, and checked the engine oil dipstick to find it way overfull with red stuff.

Drained oilpan, and about 10qts of ATF came out where 7qts of 10w30 should have been.  Filled back up with oil, drove it to confirm it wasn't somehow spontaneously exchanging its' own fluids, called them, and gave the truck back- upon examination they immediately noticed what had happened and apologized profusely.

Current plan is several oil and filter changes in rapid succession, all at the shop's expense.  I trust them to do this since it now has the owner's attention.

What else should I look at?  What's the likelihood this seriously shortened the lifespan of this engine?  I'm hoping (and I'm sure the shop is too) that if we don't see/hear anything scary in the next hundred miles and several oil changes it means things are fine and at worst maybe the clearances in this engine are slightly looser now.

It'll probably be fine.  If pressure at idle was fine, the ATF is probably not thin enough to have hurt anything.  And assuming it wasn't foaming up too badly from the overfill and wrong fluid (foaming being the likely cause of low pressure at high RPM), I doubt any major damage was done there either. 

Once it's flushed out with oil, if pressures are back to normal (particularly at hot idle) and no funny noises, I'd call it good. 

I've run ATF in the crankcase before for cleaning purposes, but always with a quart of oil, and I never put any load on the engine, I just revved it in neutral to warm it up, then dumped it. Overfilling it with ATF only then actually driving it is more extreme. So, in short, I don't know. ATF isn't necessarily harmful, but it certainly isn't going to protect bearing surfaces like actual oil does.

In reply to rslifkin :

Pressure never dropped below 20psi that I saw, pressure cold was pretty normal which is why it slipped by me for a little while.

Oil analysis? 

Do shops have insurance for these screw ups?

Has the shop notified his insurer? Even if just to get them to make a formal statement. 

In reply to John Welsh :

Oil analysis does seem potentially worth something here, I'll ask about that.  We haven't talked insurance or anything, I trust the owner and trust that it was truly a brainfart by one of his employees so I haven't been pushing for anything more than "do what you think is right and we'll go from there."  I'm sure if it starts making scary noises or has bad oil pressure the discussion will continue, although I'm a little worried about that happening a couple thousand miles from now instead.

There are people that say a 50/50 mix of atf and oil will help desludge an engine. I've never tried it.

Isn't ATF about 30w oil in viscosity? I mean, it's put in manual transmissions so I assume it can lubricate somewhat well and it's used to higher temps.

I'm not sure its the worst thing ever, I definitely wouldn't do it on purpose

Antihero (Forum Supporter) said:

Isn't ATF about 30w oil in viscosity? I mean, it's put in manual transmissions so I assume it can lubricate somewhat well and it's used to higher temps.

I think most are around the viscosity of a 5W-20.

In reply to Antihero (Forum Supporter) :

I did 3 quarts ATF and 1 quart 15W40 as a flush in miata to great results. But that was idling for an hour before draining.

It can be found in the internet as 2twisty flush or something like that.

The idea being all the extra detergents and thinness of the ATF would cleanup sludge deposits, and at least judging by the chunks that came out when I drained the pan, it sort of worked.

So nonack, you should be alright, although miata and they are wildly different engines

How hard is to get the oil pan off?  Maybe worth inspecting the bearings?

I bet it is fine.  ATF is a light weight oil, and I've also used it in engines to help clean them out.  It doesn't sound like you used the truck hard or for much time, I bet it will be totally fine, just a little cleaner.   Perhaps another oil change in a few hundred miles to help purge what is left.  

Document everything so you have a record. If the engine takes a E36 M3 in 1k, 5k, 10k miles maybe it can be traced back to their screw up and youll have the proof that there was an issue originating with their shop.  Even if you trust the owner, when it comes time for them to pay, you need something in writing. 

It would be interesting to see the oil guy chime in on this one.       

Get the oil analysis after whatever the proper interval for running oil before analysis is.

Doing it right after multiple oil changes probably won't say anything.

Definitely get the owner to acknowledge in writing this happened.     But If the engine goes bad in two years his culpability is a lot  harder to prove.  

Antihero (Forum Supporter) said:

There are people that say a 50/50 mix of atf and oil will help desludge an engine. I've never tried it.

My main concerns would be that you might have run into a situation where the ATF desludged the engine in an undesirable way: Either by having the sludge migrate to someplace it could clog an oil passage, or a situation where the sludge was the only thing holding the oil inside the motor. If you don't get metal in the oil (run an oil analysis) and don't see new leaks, you should be OK.

¯\_(ツ)_/¯ said:

In reply to John Welsh :

Oil analysis does seem potentially worth something here, I'll ask about that.  We haven't talked insurance or anything, I trust the owner and trust that it was truly a brainfart by one of his employees so I haven't been pushing for anything more than "do what you think is right and we'll go from there."  I'm sure if it starts making scary noises or has bad oil pressure the discussion will continue, although I'm a little worried about that happening a couple thousand miles from now instead.

UOA isn't designed for this. As longas oil pressure stayed above the minimum and the engine was under high load, you'll be fine. ATF starts around a thin 5W30 and usually thins down to a 20. 

Along with what everyone else said here, I wonder if overfilling it may have helped protect it.  Get the fluid level at the bearings and for sure you're going to get foaming, but it will also be easier to maintain a film level on the bearings.

Also, depending on the fluid, a lot of ATF fluids have similar ad-packs to an engine oil so if it had to happen, I'd rather have ATF in the engine then engine oil in the trans.

Thanks for the voices of experience and educated guesses guys, I guess we'll see how this goes but it sounds like if it's not failing now it's unlikely to?

To everyone saying "document to show their liability later" I get it, but seems like a real long shot to claim it's their fault after another couple thousand miles of towing on a 20yr old truck.

I mean, yeah. It might have shortened the life of the engine in long run by a little. Unfortunately there's no way to tell how much. So instead of 350k miles, it may now only last 320k miles.  Or it may have done nothing but clean a bunch of varnish and crud out of your old engine

doesn't ATF contain anti-foaming additives?

AngryCorvair (Forum Supporter) said:

doesn't ATF contain anti-foaming additives?

usually. At least good ones do. 

Your valve cover gaskets will likely leak now due to the deposits having been cleaned out. I expect fouled plugs in 5-10k 

Eons ago I had an old Buick with a lifter ticking.  Talked to an old school mechanic and he said to add quart of atf and run it till the next oil change.  I  did and it quieted down.  No damage to the engine. 

Should be fine. I knew guys who would run straight ATF in their heavily abused V8s as a "Clean Er Out" cycle in oil changes. Meaning, run til it is oil change time, then back to oil. I did not see these engines after say, 10K miles, but I bet it's fine.