2004 4l80e hot trans on hills

Hey this sounds too familiar... have a k3500 2004 had the same exact issue. First off and trust me on this. Are the brake lines rusted? If so have them replace along with the booster pump on the front of the engine and the steel coolant lines. For the first year or so i owned the truck engine/tranny temp kept climbing on 6% grades it would red line on really hot days. (See my posts) changed the fan clutch, belts, hoses, waterpump, all help but still same issue. We were up in ossippee, nh 2hrs from home heard a high pitch whine then it stopped as we crested the hill, engine temp and tranny temp all went normal. going down steering felt weird so i tapped the break right to the floor used trailer breaks to stop at a truck pullout near mcdonalds. garage replaced the booster pump which supplies fluid for steering, and brakes. A piece of rust jammed it up and cause it to stop cooling which took away coolant from the tranny and engine. the coolant was too hot. A week later relocating the trailer the brake lines let go stopped with trailer breaks again $600 for the booster pump $635 for new break lines.

3rd gear 15% for 1/2 mile secondary grade is screaming 3rd gear all the way up. The speed limit is 45, I normally climb it at 50 mph unloaded, with no trans heat concern. During towing the speed is maintained 40 mph (normal), and the engine was not lugging or in 2nd.

My guess is that it might be in 3rd gear and you may even have the gear shift set to "3", but the TC is running 'unlocked' to be able to hold your speed??

One way to tell is while you are climbing the grade, give it some throttle and if the rpms rise a bit (couple hundred rpms), but you don't gain any appreciable speed, the TC is unlocked. If you do that and the rpms don't move and it sounds like you are bogging the engine, then it's locked.

My old 97 F150 would do that at times in either 2nd or 3rd gear. If I was in 2nd and it was unlocked, if I put the pedal to the floor, it would lock the TC and I could see the trans temp go down as I drove the remainder of the grade. If it was in 3rd, it would simply downshift to 2nd because I don't have a "3" on the gear lever (it was D, 2, 1).

Good luck!

Mitch

I would never flush a transmission, that washes all of the junk to places it wouldn't be otherwise, probably blocking most of the cooler; just drain and refill,change filter, a couple of times if need be.. Mine runs around 150 normal and 180-190 towing 7000# camper.

akcooper, you don't want it to run too cool, ideal is around 180 I think, too cool and moisture does not evaporate in transmission

ib516 wrote:
How are you monitoring trans temp?

After check my stock gauge against a secondary source, I found the stock gauge to be accurate and reliable....

How are you monitoring trans temp?

interstate highway 6% grade at 60 mph or secondary road 15% 1/2 mile climb at 40 mph. both conditions tow haul on/locked in 3rd. all hills low weight, stock ride height

My 4l80e ran ‘hot’ when I was towing my toyhauler (10K loaded) and I didn’t feel comfortable with the tranny at 190 – 230 degrees. So I installed a Tru-Cool 40K. I now tow at 155 degrees in 100 degree weather with the highest temp being 185 pulling grades.


I think its obvious why the stock cooler doesn't work so well:




Here is the installed I copied when installing the cooler on my 2500hd:

http://www.gmfullsize.com/forum/showthread.php?t=253688

For a comparison I have a 2007 2500HD 6.0L 3:73 axles and tow a 6500# trailer.
I tow on hills all the time here in Idaho and in Colorado my transmission temp has never gone above 205. The one time it did hit 205 was during 100 degree weather and crossing Thompson Pass. normal towing is 150-180.

Lifted?

Over sized tires?

Both reduce ratings and efficiency

Automatics are hydro fluid coupled and has a 10%-15% or more slippage. Inherent
in how they work.

Why they invented the TC lockup to remove that slippage, but lost is the torque
multiplication of hydro fluid couple that a TC's design enjoys

That slippage is why ATF gets hot, mainly. There are also losses in the planetary's
and bearing, but minor in comparison to the hydraulic slippage (shearing of fluid)

Also, what are your weights and speeds/terrain/etc you drive?

Heavier poses more stress on the TV & components...therefore more heat generated
by the TC.