# What would make a 4L80E transmission overheat?



## TPCLandscaping (Jan 19, 2012)

Just put a re-man 4L80E in my 99 3500 chevy and within 60 miles its already burnt the fluid. I don't have a tranny temp gauge in that truck so i wasn't able to monitor that. I put about 20 miles on it and checked the fluid and it was fine. I did some sanding during that 20 miles but no pushing. I went out to push this last storm and by the time i had finished my 3rd property i could smell something hot and figured it was transmission fluid. Sure enough when i pulled the dipstick the fluid was smoking and it showed that it was "over full" on the dip stick. Now when its cold i checked the fluid and it was at the "hot" mark which means the transmission is over full. It didn't show this when i checked it at the 20 mile mark. Could the cooler be plugged? would the transmission be able to bypass the cooler if it was plugged?


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## Mark13 (Dec 3, 2006)

Depending what happened to the last trans the cooler/lines my be plugged. 

In my experience every time a truck gets a "new" auto trans the cooler and lines are flushed out or replaced. It's not fun to spend more money on top of the cost of the trans but it's better then ruining a new transmission. A few hundred in parts is better then a $2k or more transmission. Especially if you get into the modded diesel stuff and your looking at a trans that easily could be $4k or more.


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## TPCLandscaping (Jan 19, 2012)

i ran flush threw the cooler then compressed air. we used soft transmission lines to tie everything together instead of hard lines. Im feeling like i should have put a new larger cooler in just because this truck is used 90% for plowing


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## dieselss (Jan 3, 2008)

It should have 2 coolers. One in the rad and one if front of the rad. Did you flush both 
The reason its overfilled hot is normal.


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## TPCLandscaping (Jan 19, 2012)

i think the lines just run to the one in front of the radiator


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## dieselss (Jan 3, 2008)

I find that hard to believe that there isnt any going to the radiator. I could be wrong but on all our auto trks theres always 3 lines and a rad and external cooler


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## maxwellp (Feb 16, 2013)

Did it ever get foamy? Over full will kill a transmission. Would not be the first bad rebuild. Can you take it back to the re builder?


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## Midwest BuildIt Inc (Nov 14, 2004)

you said you used soft lines, even the long ones, from trans to cooler? could it be collapsing the lines pulling fluid through? or the heat is swelling the lines and the inside is getting smaller and not getting enough flow?

also, unless the front trans cooler is huge. probably not big enough alone to cool trans. should go through radiator too.


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## derekbroerse (Mar 6, 2004)

Always run thru the radiator cooler first, then the AUXILLERY cooler... its meant to help, not do the whole job. Hard tubing is better than soft lines (which I am assuming you mean hose)... and there is nothing wrong with reusing a cooler in good condition with a thorough flushing/back flushing.


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## TPCLandscaping (Jan 19, 2012)

maybe the lines aren't stiff enough… i feel like something is clogged… putting a new cooler and new lines on today. I would think a rubber line would be fine since you see a lot of race cars and hot rods using rubber lines to their transmission coolers. 

i'll look and see where the lines go a little better. I really thought all my basis were covered when i flushed the cooler lines clean. I got this transmission out of a shop in denver colorado, so i can't just pull it out and drive there to have them look through it.


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## TPCLandscaping (Jan 19, 2012)

yes it does run into the radiator first then out to the cooler.. pulled the return line off and the fluid flows with no problem.
I just pulled the transmission out and it will head back to the builder and they will hopefully send me another one asap!


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## Whiffyspark (Dec 23, 2009)

TPCLandscaping;1750454 said:


> maybe the lines aren't stiff enough… i feel like something is clogged… putting a new cooler and new lines on today. I would think a rubber line would be fine since you see a lot of race cars and hot rods using rubber lines to their transmission coolers.
> 
> i'll look and see where the lines go a little better. I really thought all my basis were covered when i flushed the cooler lines clean. I got this transmission out of a shop in denver colorado, so i can't just pull it out and drive there to have them look through it.


Rubber lines to aux cooler is fine. Rubber lines from trans to main cooler isn't


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## TPCLandscaping (Jan 19, 2012)

Whiffyspark;1750964 said:


> Rubber lines to aux cooler is fine. Rubber lines from trans to main cooler isn't


why isn't that ok? i had a gm tech look at it tonight as i was pulling it out and he said the rubber lines were fine. They are the orange high pressure hose.


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## derekbroerse (Mar 6, 2004)

They might be 'ok' they just tend to be more prone to getting cut, pinched, rubbed thru, torn off on snow banks, etc.

Also keep in mind the steel tubing acts like additional cooling capacity, radiating the heat, where the rubber will tend to insulate it and keep it in. Let's just say the factory knew what they were doing when they put steel tubing on the truck instead of hose...

Part of your problem? Not necessarily... as long as it isn't pinched over in a bend or something. But it's not helping either.


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## TPCLandscaping (Jan 19, 2012)

derekbroerse;1751618 said:


> They might be 'ok' they just tend to be more prone to getting cut, pinched, rubbed thru, torn off on snow banks, etc.
> 
> Also keep in mind the steel tubing acts like additional cooling capacity, radiating the heat, where the rubber will tend to insulate it and keep it in. Let's just say the factory knew what they were doing when they put steel tubing on the truck instead of hose...
> 
> Part of your problem? Not necessarily... as long as it isn't pinched over in a bend or something. But it's not helping either.


well that makes sense! 
transmission shipped back to the shop yesterday, and of course calling for a storm thursday into friday……then calling for more snow at the beginning of the week. hopefully my dodge holds up..


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