What the freak is up with my transmission temperature!

[brycebba]

I have a 96 3500 CCLB with a 4L80E and have done the super cooler mod that there is a sticky for which is only slightly larger than stock but a better design. I have my temperature sending unit in the transmission pressure test port and cruising on the highway or city long enough it will heat up to 180 or 190 but no higher. I was kind of ok seeing that with a bunch of city driving where the torque converter hardly locks up but on the highway when it locks I don't understand why it doesn't cool.

I had a 03 cummins that acted this same way but it was because it had a heat exchanger that runs the tranny fluid along side the antifreeze to help heat the tranny fluid but that gets it too hot almost to operating temps. I bypassed that and the trans never got above 200 even towing my 28ft trailer with a 16ft 4 wheeler trailer behind that unless I was in the city.

Our trucks don't have anything stupid like that do they? I didn't notice it but is there a flow specific direction to those B&M coolers? I don't even want to try towing my trailer for the first time until I get this figured out. Btw, had my favorite trans builder look it over and do a fluid change just after I bought it 6 months ago and he said it looked amazing and the truck only has 66k on the clock

 

[brycebba]

Bumpity bump bump

 

[Coveman]

On my truck there is a trans cooler nested in the radiator. Are you running both the factory cooler and the B&M?

 

[brycebba]

I pulled the factory cooler that sits in front of the radiator and replaced it with the B&M cooler. So you are saying that we do run the trans fluid through a separate part of the radiator?

 

[brycebba]

Now that I got that info from Coveman, thanks btw, I found this image below in a thread here. http://www.gmt400.com/forum/showthr...-please&highlight=radiator+transmission+fluid

I HATE THAT SETUP!!!!!! My cummins had the same stupid design except it was an external exchanger that ran coolant and ATF side by side. What a load of crap. <sarcasm> Lets heat the tranny fluid to as close as operating temps as we can get so that when anyone tows it will likely overheat quickly....lets also put it in the same radiator or locations as the coolant so if the radiator cracks, which they never do, the two fluids will mix and toast the tranny and put the engine through misery </sarcasm>

Well I can tell you exactly what is happening this weekend, I am capping off that POS setup and running the trans lines directly to the cooler and back and bypassing that junk. I would be willing to bet that I drop 50 degrees easy. My cummins would heat to 210 towing my trailer up steep grades and never drop below 180 in the summer even when I wasnt towing. After my trans guy bypassed that exchanger it ran at a cool 160 when the TC was locked even when towing and would only heat beyond that if it unlocked or I was stopped dead in traffic.

I know I will get the same argument here as there was on cumminsforum where true experts, no sarcasm, would strongly disagree saying that the transmission would run too cool in the winter and it would get damaged. I decided that the risk of damaging it was worth the mechanical risk of fluid contamination. 3yrs later and the trans always performed top notch and looked great at every service.

Only thing I dont know is whether or not I am ok to run rubber lines with clamps or if I really need professionally made hard lines.

You must be registered for see images attach

 

[volunteerff21]

There IS a cooler built into the radiator, the cooler you replaced is an "auxilary" cooler.

Here maybe this will help

You must be registered for see images attach

EDIT: Seems you figured it out a second before I posted

 

[brycebba]

That is a much better image than the one I found. Thanks for that! I'm kind of wondering if I can just relocate the B&M cooler and just use the lines that went into the radiator based on that image

 

[brycebba]

Mine seems to be a little different. Do you by chance have that same type of diagram for the 4L80E?

 

[volunteerff21]

There should be 3 different lines for a 4L80E (going off memory since my current 454 doesn't have the auxiliary cooler)

1) From tranny to upper portion of radiator
2) Lower radiator to one side of auxiliary cooler
3) Other side of auxiliary cooler back to tranny

That diagram is just the image LMC uses in their catalog, although I'm 99% sure the set-up was the same for all the trucks.

 

[brycebba]

Yep that looks spot on. I think I will either have to just join the two radiator connections with a fitting or have to run new lines. Maybe for a proof of concept I will just join them and then if I like it I will have new lines bent or something


Edit: any idea what that coupler size would be. I think I could either do a straight or elbow fitting