4L80e Overheating

Kratos707 · August 21, 2017

I was wondering if anyone has had this problem with there 4L80e transmissions. On my truck the transmission overheats when driving with no load on rather mild days (75 degrees F). My truck is a 2006 2500hd 6.0l 4x4 and I have an extra trans cooler in addition to the factory auxiliary cooler. Initially I was thinking that my coolers were plugged because the line coming from the transmission was hot and the line returning from the coolers was the same as ambient temp. Thinking that the coolers were plugged I tried flushing them, forward and reverse, I even removed them, and I still get that condition of one cooling line being hot and the other being cold. I started to think that maybe the cooling lines have a blockage so i flushed them as well (both forward and reverse) but still the same problem ( i also verified that the radiator did not have a blockage since the heat in the line is past the radiator). Since this did not work I took the truck in to have the transmission flushed just in case there was something going on the the transmission. The shop checkout the pan, filter and fluid and said it looked good (no metal shavings, minimal debris, not burnt). This shop used the HotFlush system to flush the system. Even after the flush the same problem.

The system is acting like the transmission is not letting the oil back into the transmission from the oil cooler return line. Does anyone here know what could be causing this? Outside of this issue the transmission is stock and is running fine.

please help

thanks

Swimmer8366 · August 21, 2017

Sounds like a suck cheat valve ....

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Kratos707 · August 21, 2017

Swimmer8366, sorry for my ignorance on this but I am new to working on these trucks. What would it take to fix it?

dewfpo · August 21, 2017

Have you checked out the dash gauge to see if it's reading accurately?

Did this problem start all of a sudden or have the temps been climbing up over time?

What temps are you seeing?

DEWFPO

Kratos707 · August 21, 2017

Hi dewfpo, I have checked the dash gauge (confirmed the pan was hot with a temp gun). I recently bought the truck used and after about a month I noticed that temps were getting to the red zone on the temp gauge. After i did the transmission flush it seems like it worked for about a week before it started up again. Last night I flushed out the cooling lines (again) but still seems like no flow through the cooling lines.

I have hit the temp warning twice and it is not uncommon for the truck to have the trans temp around 220 when it is 75 degrees out side. (this is with both trans coolers and on the freeway going about 65 - 70 mph)

Raptordude · August 21, 2017

I would not drive the truck past 220 degrees anymore, if you test drive it and temps rise over 220, shut it down and let it cool

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dewfpo · August 21, 2017

Hi dewfpo, I have checked the dash gauge (confirmed the pan was hot with a temp gun). I recently bought the truck used and after about a month I noticed that temps were getting to the red zone on the temp gauge. After i did the transmission flush it seems like it worked for about a week before it started up again. Last night I flushed out the cooling lines (again) but still seems like no flow through the cooling lines.

I have hit the temp warning twice and it is not uncommon for the truck to have the trans temp around 220 when it is 75 degrees out side. (this is with both trans coolers and on the freeway going about 65 - 70 mph)

Disconnect the atf inflow line to your trans (and put a hose on it into a pan) and have someone start it for just 5 seconds. You can then eyeball the flow coming out of the coolers and back into your trans to see if you have good flow, low flow or no flow.

Does the gauge and your temp gun come close when you compare them?

220F is not normal but it's not going to kill your atf either. If it gets to 240-250 then I would worry some.

You said you 'tried' flushing the coolers. Did you get good flow thru them?

DEWFPO

Kratos707 · August 21, 2017

DEWFPO, I actually compared the temp gun to the temp I was pulling from the OBDII and the it was pretty close. the gun read slightly lower but I think it was because the pan is a gloss black.

I will try the connection of the tube to the input line to measure the flow.

As for the flushing, the flow was really good I used an electric pump to to run oil from both directions. when running in the reverse direction I let the system run for about 15 minutes. I did this after I blew out the lines with compressed air.

Formulabruce · August 22, 2017

When I install a Cooler, I REMOVE the stock one and replace it with a B&M super cooler and put it in its place. Its about twice as wide and 3X as high and twice as thick. I only add one L shaped bracket. I am Not an advocate of running coolers in series. Would like to see a picture of your cooler set up behind the grille.

Kratos707 · August 22, 2017

So on my 30 mile drive home today I noticed that my trans temp did not go over 160 which is unusual cool temp for what I am used to. Once I got home I touched the return line and it is finally warm. I am not sure why it is now working but I am going to monitor let you guys know what happens.

As for the set up on my coolers is currently I am running one 11x11 derale cooler that is sitting to the passenger side of the GMC on the grill. I used to have it hooked up in series after the stock auxiliary cooler. After it runs okay for a while I am going to run a second 11x11 cooler (because I have a second one) but set up a parallel system. Not sure if it will work but I was going to set it up and see how it runs.

davester · August 22, 2017

maybe something finally broke free so you could get good flow through the coolers.

My truck, with the stock "HD" transmission cooler setup (through rad, then through aux cooler), I don't think I've seen it hit 90C (195F), even on a hot day driving around in traffic.

Kratos707 · August 25, 2017

Just wanted to give a quick update on my truck. The trans temp has been good for the last couple days and even when getting close to 90 out the trans is still running cool (not over 175 on the freeway). I bought replacement lines to swap out once I have time, but the only thing i could think of that was causing my problem before was a partial blockage at the inlet of the transmission (returning cool oil connection). That like you said Davester must have come free and allowed full flow again. This weekend is going to be near 100 and I will check how the transmission runs.

thanks all for the help with this!

davester · August 26, 2017

make sure you've got the right lines, as they are different between the 'regular' transmission cooler lines and the HD lines.

Kratos707 · August 26, 2017

Will do, davester, thanks for letting me know, because I had no idea there were different lines for the hd's.

davester · August 27, 2017

Should have included this with the previous post, but you can either:

a) go to the dealer with your vin, and they'll sell you the right lines

b) ask for the build sheet from a dealer (or various online sources of it, should be able to do it for free) or you can decode the RPO codes on the sticker in your glove box. It's a long list of all the options for your truck, and it's useful to find the right parts for your truck, as there are options that make a difference as to what parts you need to buy (transmission lines, brakes are two I know of offhand).

If you don't have to have the parts right away, buy them online from places like rockauto.com (and use their 5% discount code available all the time), generally significantly cheaper than local parts stores..

And for doing the transmission lines, don't forget to also buy replacement retaining clips, as they are single-use (you will need either 4 or 6 depending on if you have the HD tranny cooler and if you replace all the lines).