Transmission Overheat - 10R80

Joined
Jun 8, 2016
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2,691
Location
Texas, USA
Hey guys,

Took the car (2018 Mustang Ecoboost) on its first highway trip this weekend. No issues going, big issues coming home. It's about 110 miles of various highways.

Did some 'spirited' slow traffic passing on a few occasions, and got about 5 miles from home and the transmission started acting indecisive on which gear it wanted to stay in. Flipped the gauges over to transmission temperature and it was at 215. Just kept a steady throttle, and it kept climbing to 225. I took the next exit and stopped.

I smelled transmission fluid as soon as I opened the door. There are a few drops hanging from the cross brace, and the exhaust flex joint was smoking.

I raised the hood, turned the heater on full blast and let it idle. It slowly dropped to about 195, so I continued home. It pretty much stayed at 195 for the next few miles of stop & go. Got home, and the cooling fan ran for several minutes after shutdown.

My discovery 10 minutes later: I took off the radiator shroud, and just started feeling around. The cooler in the middle is STONE cold on its top, and as far down as I can stick my fingers. Shouldn't this thing be burning hot?

I was assuming that this transmission may be one of the units that made it out of the factory underfilled, but I'm now also wondering why the transmission cooler wouldn't be even a little warm, if its full of overheated fluid. Thermostat not working?

I've never had an automatic overheat when I'm playing around passing slow traffic on the highway.

2018 with 31,000 miles, warranty start date was March 2018, so I'm assuming this will be a warranty thing, whatever the problem may be.

Any insights?
Cooler.jpg
Drip2.jpg
 
Joined
Mar 15, 2016
Messages
82
Location
Florida, USA
Ford has a thermostatic valve built into the oil lines feeding the ATF cooler, at least they do on F150's with the 10 speed. That valve doesn't open until 190 degrees. The 10 speed on my truck runs at 206 to 214 degrees all the time. Removing that valve on the F150 will result in a 'transmission under temperature" CEL.
I am assuming that Ford has something similar on your Mustang, and it sounds like this valve is not opening, or at least opening erratically.
 
Joined
Oct 9, 2004
Messages
12,876
Location
Cincinnati, OH, USA
Something isn’t right-but I’m not sure 225F would be considered super hot for full synthetic ATF(?) I’ve gotten Dex III that hot when towing and the fluid survived it. The 10R80 in the new Transit has issues getting in the correct gear too, sometimes flares & bangs, and I don’t think I’ve ever gotten it that hot.
 
Joined
Feb 20, 2007
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6,422
Location
Southeast
I’ve seen my 10r80 at those temps plenty when towing and zero issues. Without checking, 250F is probably what id call the “oh sh**“ temperature.

your mustang is plumbed different than my 150. Yours has a front cooler, while mine has a water-to-atf exchanger at the transmission. I’d think yours has that too for pre-warming, and that forward cooler may be an aux for when it’s really hot. Do you have the at-trans exchanger?

the trans does have a dip stick. Passenger side, 19mm wrench, suggest close-ended wrench, reachable from the bottom. its an inch tall, and a baby dip stick will be inside of it. Suggest checking the fluid level. Sorry, it’s going to be a tight squeeze.
 

WylieCoyote

Thread starter
Joined
Jun 8, 2016
Messages
2,691
Location
Texas, USA
I can't speak to how it's plumbed at the transmission. I have been under there but didn't look specifically for that. I really think this is at least partially cooler related, because for the transmission to be that hot and the front cooler to be cold to the touch is a sign of something amiss, to me, along with the spewing fluid. If I had a lift I would have checked the fluid level, but checking it on ramps is completely inaccurate. So it could also be overfilled, or underfilled, which was somewhat common on 2018s from the factory.

Also important to note that I have a 2018 convertible that has never done this. I've never seen transmission temp above 200 on any 2.3 Mustang I've had. I guess it actually reached more in the 235 range as it was pointing at the last marker before 250 when I pulled over. Hope they figure it out tomorrow, and it doesn't need a new transmission. Lord knows how long I'd have to wait for that.

IMG_20220410_204504056.jpg
 

WylieCoyote

Thread starter
Joined
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2,691
Location
Texas, USA
Update: Service writer said trans pan was leaking, causing a low fluid situation, causing erratic shifting and overheat.

Funny that the pan was bone dry until the transmission vented fluid last week. So, either they haven't found the root cause, or it was underfilled from the factory and they're just not saying it.

Time, and another highway trip, will tell.
 
Joined
Oct 30, 2021
Messages
229
Update: Service writer said trans pan was leaking, causing a low fluid situation, causing erratic shifting and overheat.

Funny that the pan was bone dry until the transmission vented fluid last week. So, either they haven't found the root cause, or it was underfilled from the factory and they're just not saying it.

Time, and another highway trip, will tell.
At least you gonna get some fresh fluid
 
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