Kratos707

Want to give another update on the transmission. I haven't had a chance to replace the lines yet but the transmission is running cooler. Today it was 110F out and the trans temp was about 190 to 200F. I haven't had any issue with overheating since the last update. I think the problem was a blockage at the transmission inlet which must have pushed through. I still plan on changing the lines since they are the original lines.

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

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!

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.

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.

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)

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

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