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4L80e cooling issues - am I insane or something going on with it?

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Hello gents and ladies,

For the past a year or so I have been constantly thinking that my transmission (stock 4L80-e, first year) is constantly runs hot (or warmer than other trucks).

Because of this constant worry, I have been playing around too much with the cooling aspect of it. With Fall is upon us, maybe I shouldn't worry - but I figured it was time to break down and see what the hell is wrong ... or maybe there isn't anything wrong with it and it's just me being nuts ... the back story ...

My V2500 is only my tow-rig - it's not my daily driver .... it's sole purpose for me is to transport my family and our trailer within a 120 mile radius. That's it. Because it's my tow-rig, I have some some extras to it ... it has Yukon's 4.10 gearing(stock 14bolt semi-floater in the rear, 10-bolt in the front), aluminum 4core radiator with hi-flow electric fans & shroud. Amsoil transfluid pumped through the trans - and i have a mag-hytec deepmalum pan. All other fluids are synthetic. Tires are one size bigger than stock. I am taking this extra precaution since I live on the Gulfcoast where 11 months out of the year it's warmer that anywhere else on God's green earth.

But over this past summer, I saw trans temps in the pan of 205F - and this isn't towing 4,000lbs. This is just normal driving. And when I am towing it's just a tad higher. I stay at around 60-64 MPH. I generally don't like to drive fast in it.
Cooling was setup the traditional way ... trans out -> radiator -> aux cooler -> trans in. Engine would be at 180F and the Trans would be at 205F, on the interstate. Then when I get into stop/go in town, (it seems) I have both the Engine and Trans competing against each other, with the liquid-on-liquid cooling in the radiator.

Then the hair pulling starts .... I have tried everything to address this. With and without using the radiator before the huge-ass aux cooler. I tried Two aux coolers, but then the AC condenser starts loosing air flow. I even tried Dana's LPD cooler - but I don't think they're really made to used down here. Right now, I am bypassing the radiator and around town I get to 180F after it gets warmed up. Interstate stays at around 180F, but then I get into stop/go, it creeps up to around 195F. So just less than with it plumbed into the radiator.

FYI - The engine fans are set to come on at 195F and turn off at 180F. The fans never hardly run on the interstate - basically only run when the A/C is on, even with towing.

Maybe the torque converter isn't locking up? Could that be an issue - how do I tell if it's locking up or not? The trans doesn't slip - seems good - but could something be wearing out that is causing this extra heat? I don't have a shift-kit ... maybe it's time?

Anyways ... sorry for the long post. It's been bothering the heck out of me. Maybe I just do a NV4500 manual transmission conversion and call it done :dunno:
 
I guess there is one option that I haven't considered until now ... I could just re-plumb it the traditional way, and put a "pusher" style electric fan in front of the aux cooler? The cooler is 11x11 so a 9" fan would fit just fine. Um ....
 
Those transmissions are good to run to 250 degrees so I wouldn't worry too much. But that being said, I try to keep mine no higher than 220 while out and about.
What size lines are you running? Anything less than -6AN or 1/4" ID is too small. That can lead to issues.
Is your aux cooler plate fun design or tube fun? I find the plate fin works better.
I wouldn't put a pusher fan in front of it. Maybe make sure it has adequate air flow? Plug all the holes in the core support?
How you have it planned right now is good, I wouldn't change that. How many rows is your current aux cooler?
 
Your around town temps are not that high considering the location. I would not be worried about those temps especially with synthetic fluids. How are you monitoring temps? Could the gauge be a little off? That would not be unheard of. What year is the 4L80E? Do you have a tach in the vehicle? I would be more concerned that the temps are over 200 going down the road at 65mph that they are around town. This would lead me to think that the lockup clutch may be slipping or not applying at all. This can be monitored with a tachometer. Is this a 1991 model as in the signature?
 
Rugger187 said:
Those transmissions are good to run to 250 degrees so I wouldn't worry too much. But that being said, I try to keep mine no higher than 220 while out and about.
What size lines are you running? Anything less than -6AN or 1/4" ID is too small. That can lead to issues.
Is your aux cooler plate fun design or tube fun? I find the plate fin works better.
I wouldn't put a pusher fan in front of it. Maybe make sure it has adequate air flow? Plug all the holes in the core support?
How you have it planned right now is good, I wouldn't change that. How many rows is your current aux cooler?
Click to expand...


Thanks; I didn't know that the 4L80e can take on more heat. I guess I have been overly cautious. Regarding the size lines, they are the stock lines - 5/16, which go into 11/32 rubber lines to/from the cooler. Its a plate/fin style ... and I think its like 32 rows or something. It's roughly 12" x 12".
 
Greg Ducato said:
Your around town temps are not that high considering the location. I would not be worried about those temps especially with synthetic fluids. How are you monitoring temps? Could the gauge be a little off? That would not be unheard of. What year is the 4L80E? Do you have a tach in the vehicle? I would be more concerned that the temps are over 200 going down the road at 65mph that they are around town. This would lead me to think that the lockup clutch may be slipping or not applying at all. This can be monitored with a tachometer. Is this a 1991 model as in the signature?
Click to expand...

Thanks for the reply Greg. I have a relatively new Auto Meter gauge (Pro or Sport Comp ... can't remember which one at the moment). I believe it's working ... however I did wrap the exhaust cross tube with a heat wrap, hoping to cut down the temps - i.e., not heating the trans pan. The sender is in a dedicated port in the pan (mag-hytec). It's the first year of the 4L80e, 1991. It's the stock one that came with the truck; yeah, the one in the signature. Where those prone to issues like this?

I am wondering too if it's an issue with the lockup. Goes into Overdrive around 48-50MPH or so. When towing I manually shift into overdrive once I get to a good speed on the interstate (to ensure it doesn't do a lot of hunting of gears). I generally just keep it in drive around town to prevent just that.

I guess a tach is in order then. What do I need to look for specifically once it's installed and I am towing? What RPMs the transmission is shifting?

Thanks for the suggestion :waytogo:
 
An easy way to tell if your converter is locking up is to get it up to speed in overdrive. Once it has shifted into 4th, if you lightly tap the brakes, your rpm's will jump up a few hundred. If your converter is not locking up, it could indeed lead to overheating.
 
Rugger187 said:
An easy way to tell if your converter is locking up is to get it up to speed in overdrive. Once it has shifted into 4th, if you lightly tap the brakes, your rpm's will jump up a few hundred. If your converter is not locking up, it could indeed lead to overheating.
Click to expand...

This, and you should also be able to crowd the throttle slightly when in 4th around 55mph and the tach should only rise incrementally, if you see a few hundred rpm jump at very slight throttle input the clutch is releasing. It should release under larger throttle inputs as dictated by the TCM just as it does with a total lift of throttle.
 
Thanks Greg and Rugger. I will be able to take it on the road this coming weekend and test that out. I do recall however that I don't think the RPMs go up after tapping on the brakes when in OD. IIRC, the RPMs will drop and almost what seems like the trans would shutter before dropping into 3rd. That is one of the reasons why I don't like get into over drive unless I know it's not going to be hunting around. I may go ahead and get a tach too. I have always been curious to what the RPMs have been.

Greg, what do you mean exactly "crowd the throttle slightly"?

Thanks again for the replies.
 
I mean very gently apply the throttle progressively till the computer signals to unlock the converter. Kind of like shooting, you want to slowly squeeze down so you can feel and hear what is going on.
 
I did some driving tonight and really paid attention to when the truck shifts gears. The following is an average, over about 30 minutes of driving, which included several long stretches.

1st -> 2nd ~ 10MPH
2nd -> 3rd ~ 22MPH
3rd -> 4th ~ 42MPH

After reaching ~42 and all the way up to 70, I tried at several points to lightly tap the brakes and/or just let go of the gas. At no point did it 'seem' to climb in RPMs. The RPMs continued to drop as the truck lost speed - until I reapplied gas.

This initial testing is telling me that the tc lockup is not engaging. Would that be an correct statement? Could explain my horrible gas mileage as well as the point of this thread - high heat.

I bought a tac tonight. I am going to see about wiring it up in the morning and do another round of testing w/ the RPMs. I will report back.
 
I got the tach hooked up and drove around for about 45 minutes. Basically did the same path as last night, but there was a bit more traffic (there is an art festival happening downtown today) - so more stop/go.

I am turning about 2000 RPM at 58MPH and about 2500 RPM at 68-70MPH. I went through the same motions as I did last night ... and the RPMs would drop when at 65MPH or so, take my foot of the gas and just slightly apply brake. There was no change in RPMs until I coasted to about 35MPH, replied throttle, and it transmission kicked dropped down to 3rd.

Sounds like a non-functioning tc lockup then eh? Is this commonly repaired by a sensor within the transmission/valve body?
 
I did some initial checking online; apparently some folks that are experiencing lockup issues, find out that it's their brake switch that is the issue.

I just took a look at my switch (and the associated wiring) and i found a hack from the previous owner. I don't know if the switch needs both plugs plugged in, but I only have one. Furthermore, the orange wire coming from the harness has been cut and the orange wire on the switch side has been plumbed into another circuit. I have no idea if this is causing the TC not to lock up, but I guess I will review the diagrams from AllDataDIY. I am curious that my switch has provisions for two plugs, but only one is plugged in. I don't see a loose plug in the immediate area either.

Here is a pic that I just took. Thoughts?

brakelight-switch-hack.jpg
 
There is a very strong chance the brake switch and non lockup are correlated since this is an integral part of the TCC system. Let us know what you find in your wiring investigation.
 
Greg, I just downloaded two diagrams from AllData. One is the DRAC and VSS items, and the other being the Brake light Switch stuff connecting into the DRAC and ECU. I see that there is a plug, that is purple (going to the ECU - labeled 'BRAKE SWITCH') and pink/blue going to +12V. This is shown to the be the 2nd plug ... the one that is apparently missing from my switch.

So I going to start hunting down this missing plug. Ugh.
 
It was obvious when I just went back out there ... the purple was cut and the pink was reused to supply 12v to the lamp side of the brake switch. Pic below.

Looks the previous owner tried to do some additional hacking but then ultimately just left the purple just loose. Purple one is the one that goes to the ECM - and as of right now, it thinks the brakes are applied (open circuit) - makes sense, since the lockup never occurs. This circuit to the ECM is only closed when the brakes are not applied.

I am on the hunt for a new plug. I found one at Rock Auto ... AC Delco PN: PT110. Maybe I can try to find the equiv from a local parts store. I will report back once I get this plug in and do another round of test driving.

brakelight-switch-hack2.jpg
 
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