Chevy Silverado Hot Transmission Temps??

Rarefied

Rarefied

Line Up and Wait
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Broke Engineer
I picked up a 2014 Chevy Silverado 1500 with the v6 engine a couple months back. Everything's been good so far with mostly around town driving. I was on the interstate today going 80 and about 45 mins in, I noticed my cruising rpm had stepped up some (~200 rpm) from when I got on the interstate. I thought that was odd but out of curiosity started flipping through the menu's and saw I was getting an instant mpg of 15-16 instead of my normal 18-20 (flat ground). Kept flipping through and then saw transmission temp was at 240 degrees F!

Although this is the newest vehicle I've owned and the first with a transmission temp digital gauge, I knew that was too high. I backed down to about 75mph and the rpms lowered to more inline of where I'd expect. Presumably, all of this is from the torque converter not fully locking in, or unlocking (or whatever the correct terminology is) at the slightest incline. At 75, the transmission started cooling down and settled in around 190F. On the return trip, I tested 80 again and noticed the same thing, temps started climbing after a few minutes and cooled down when I backed off to ~75.

The prior owner put some slightly larger than stock tires on the truck, but nothing too crazy (ex: gauge says I'm doing 77-78 when I'm doing 80). From the limited search I've done, there seems to be some consensus that reprogramming the computer to account for the tires can help the torque converter lock in sooner. Have any of you experienced something like this?

This truck seems to be much more free willing to let the torque converter slip a bit compared to other vehicles I've owned, but it's also my first Chevy and the newest vehicle I've owned, so I'm not sure how much influence fuel economy programming is playing into here.

I've otherwise not noticed any cooling issues, engine temps stay fine, and haven't noticed any physical blockages on the radiators.
 
Got a trans cooler? When was the last full flush, not just drain & filter?

ETA: yes, the PCM needs to know the new tire size…whether that impacts shift points is debatable.

Also curious if the valve body ever got swapped.
 
TCABM said:
Got a trans cooler? When was the last full flush, not just drain & filter?
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According to the interwebs this year model and engine does come with a trans cooler by default, but I plan to go physically trace everything tomorrow and check the transmission fluid level.

As for the last flush, etc. Absolutely zero idea, it's possible never. I received limited records outside of regular oil change and tire rotations from the prior owner. Truck is sitting at 158k miles, so I'm concerned if its never been done, then a flush would do more harm than good.
 
I'd say a flush-n-fill is in your future at a minimum, and clean the aux trans cooler and radiator/straighten fins to maximize cooling. While the tire size may have some speedometer impact, I don't see how it would impact TC lock-up or trans temps at those speeds. You would be squarely in top gear/full TC-lockup above 60mph with no load. The high temps could have damaged o-rings that help hold pressure for the TC lockup though, so damage may already be done. Flush/fill and see what you get.
 
I have bad news for you as I’m in the middle of overhauling the transmission in my 2010. They both have the 6L80/6L90 transmission as well as displacement on demand. The DOD system is junk. At some point you are going to end up with a collapsed active fuel management lifter and have to pull the heads to either replace it or swap them out with different lifters and a non DOD cam. You should get the DOD system programmed out before it does fail. There are a few companies that you can overnight your computer to and they will program and ship it back for about $200.

The DOD system is also causing your transmission issues. When the engine switches from 4 cylinders to 8 or back the computer commands the torque converter to slip so that you don’t feel the cylinders activate or deactivate. That slippage causes the stamped cover plate in the torque converter to get hot spots where the welded mounting lugs are Those hot spots eat away all the friction material in the converter and then dumps all that material into your transmission. The result is a converter that starts slipping as well as all your other clutch packs in the transmission quickly wear out and start overheating or slipping. The only fix is to have the transmission rebuilt and use a torque converter with a billet plate so it doesn’t develop those hot spots at the lugs.

At this point I would drop the pan and see if it is full of friction material (black sludge around the magnet) and/or full of metal glitter. If it is then you need a rebuild. You can drop the pan without having to disconnect the exhaust as long as you take the heat shield off the passengers side of the transmission. It is held on by 2 10mm bolts. The pan is held on with 16 10mm bolts and once you get them out you can turn the pan past where the heat shield was and sneak it out past the exhaust to get it out.

If you get very lucky and it isn’t full of friction material then you can just address the temp issues by swapping out the transmission thermostat that runs to the cooler with an upgraded one from sonnex. That will bring the temps down about 20 degrees and can be done with the transmission still installed. If you are only having high temps at higher loads it’s likely you have burned up the clutch pack in one of the assemblies. If mechanically inclined rebuilding the 6L80/90 is pretty straigtforward and a boy needs a very large snap ring pliar and an inverted torx socket as specialty tools. If not, it’s about 4k for a rebuilt one day clouding the billet converter plus another 2k in labor to remove and install it. It’s unfortunate but both the stuck AFM lifter as well as the worn out torque converter are not so much of but when they will fail on those year trucks.
 
kmacht said:
I have bad news for you as I’m in the middle of overhauling the transmission in my 2010. They both have the 6L80/6L90 transmission as well as displacement on demand. The DOD system is junk. At some point you are going to end up with a collapsed active fuel management lifter and have to pull the heads to either replace it or swap them out with different lifters and a non DOD cam. You should get the DOD system programmed out before it does fail. There are a few companies that you can overnight your computer to and they will program and ship it back for about $200.

The DOD system is also causing your transmission issues. When the engine switches from 4 cylinders to 8 or back the computer commands the torque converter to slip so that you don’t feel the cylinders activate or deactivate. That slippage causes the stamped cover plate in the torque converter to get hot spots where the welded mounting lugs are Those hot spots eat away all the friction material in the converter and then dumps all that material into your transmission. The result is a converter that starts slipping as well as all your other clutch packs in the transmission quickly wear out and start overheating or slipping. The only fix is to have the transmission rebuilt and use a torque converter with a billet plate so it doesn’t develop those hot spots at the lugs.

At this point I would drop the pan and see if it is full of friction material (black sludge around the magnet) and/or full of metal glitter. If it is then you need a rebuild. You can drop the pan without having to disconnect the exhaust as long as you take the heat shield off the passengers side of the transmission. It is held on by 2 10mm bolts. The pan is held on with 16 10mm bolts and once you get them out you can turn the pan past where the heat shield was and sneak it out past the exhaust to get it out.

If you get very lucky and it isn’t full of friction material then you can just address the temp issues by swapping out the transmission thermostat that runs to the cooler with an upgraded one from sonnex. That will bring the temps down about 20 degrees and can be done with the transmission still installed. If you are only having high temps at higher loads it’s likely you have burned up the clutch pack in one of the assemblies. If mechanically inclined rebuilding the 6L80/90 is pretty straigtforward and a boy needs a very large snap ring pliar and an inverted torx socket as specialty tools. If not, it’s about 4k for a rebuilt one day clouding the billet converter plus another 2k in labor to remove and install it. It’s unfortunate but both the stuck AFM lifter as well as the worn out torque converter are not so much of but when they will fail on those year trucks.
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So I did know about the lifter issue prior to purchase and immediately put in a OBD plug that keeps the engine from going to 4 cylinder mode. Naturally programming the computer would be a better long term solution though. I would think this deactivation would keep the transmission from slipping though? Do you think it's just the clutches at this point or would fully programming the computer solve this?

Everything you said does make a lot of sense. It explains why the behavior seems to be default to slipping versus staying locked in. I hate that its another emissions thing, but alas. Really appreciate the information you've provided here.

I'm pretty mechanically inclined, but I'd probably at least need a detailed video showing how to rebuild one to feel comfortable doing it for the first time. Failing that, I'd at least remove and install it myself.

Fingers crossed on just being able to upgrade the cooler and maybe do some programming though...
 
Part of me is also like...well if its running fine at 75mph for now...just ignore it until it makes me do something and drive a little slower. I imagine it could eventually start doing the same thing at 75mph, but it may be 50k more miles before that happens.
 
Matthew K said:
So I did know about the lifter issue prior to purchase and immediately put in a OBD plug that keeps the engine from going to 4 cylinder mode. Naturally programming the computer would be a better long term solution though. I would think this deactivation would keep the transmission from slipping though? Do you think it's just the clutches at this point or would fully programming the computer solve this?

Everything you said does make a lot of sense. It explains why the behavior seems to be default to slipping versus staying locked in. I hate that its another emissions thing, but alas. Really appreciate the information you've provided here.

I'm pretty mechanically inclined, but I'd probably at least need a detailed video showing how to rebuild one to feel comfortable doing it for the first time. Failing that, I'd at least remove and install it myself.

Fingers crossed on just being able to upgrade the cooler and maybe do some programming though...
Click to expand...
I also had the OBD2 plug to delete the AFM function on my 07 GMC and 07 Grand Prix GXP (both had the LS-5.3L). The GXP actually developed a shudder when coming to a stop (gear 2-1) with no load, which I though was a failing torque converter and had a shop "repair" it. Turns out the problem was still there with the rebuilt trans, and it was just the AFM system causing problems. Bought the OBD2 device and the problem disappeared. That was a $2K mis-diagnosis. Not to mention the absurd oil burn rate on both vehicles which was over 2qts per 5K miles and fouled out the catalytic converters on the GMC. Then the LS-series motor mounts which fail in 100K miles or less. I think your problem will be actual transmission wear, not what the AFM system is doing, especially since you have the system inactivated (although the lifters still eventually fail).
 
Matthew K said:
So I did know about the lifter issue prior to purchase and immediately put in a OBD plug that keeps the engine from going to 4 cylinder mode. Naturally programming the computer would be a better long term solution though. I would think this deactivation would keep the transmission from slipping though? Do you think it's just the clutches at this point or would fully programming the computer solve this?

Everything you said does make a lot of sense. It explains why the behavior seems to be default to slipping versus staying locked in. I hate that its another emissions thing, but alas. Really appreciate the information you've provided here.

I'm pretty mechanically inclined, but I'd probably at least need a detailed video showing how to rebuild one to feel comfortable doing it for the first time. Failing that, I'd at least remove and install it myself.

Fingers crossed on just being able to upgrade the cooler and maybe do some programming though...
Click to expand...
I had one of the Range obd2 adapters that turned off the DOD system but it still ended up with a collapsed lifter at 160k And the transmission going out at 210k. I bought the truck with 130k and installed the adaptor at that time. It will certainly make it last longer but it’s still going to fail at some point if the person before you didn’t use it from the start. it’s just a bad design and the AFM lifters will start leaking at some point even with the DOD system disabled. If you do end up with a collapsed lifter in the future just get the full kit with the standard lifters and new cam. It’s about 1k in parts but not a whole lot more work than just replacing the lifter with another AFM one.

The factory service manual for the transmission is about $60 and covers everything. I also recommend the book below because if you rebuild it you are going to want to fix some of the transmissions other shortcomings. The factory manual only covers how to put it back completely stock.


If I were you I wouldn’t do anything else until you drop the pan and see what’s been collected in there. If it’s clean then install the revised thermostat to fix the temp issues and hope you get more miles out of it. If it’s got metal flakes and friction material in there then you know the transmission needs to be pulled. Whatever you do don’t just keep driving it. If it’s got metal and friction material in there it will eventually start wearing out and scoring the pump which is another $700 to replace when doing the rebuild.
 
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