6L80E running hot

[87Skier]

Just did an engine and transmission swap and have been monitoring the transmission temps. I know the 6L80/90's run hotter than the TH350/TH400 and 4L60/80 stuff, but my transmission likes to stay around 220 F. It can easily climb passed 240 F while climbing long grades. This is all in 30-40 F weather, not even mid-summer extremes.

My current setup uses the transmission cooler built in to my radiator, along with an external unit. The external unit is probably undersized, but it was already setup from the turbo350 it had in it before.

I feel like I'm out of options and need to upgrade to something like this: https://www.summitracing.com/parts/der-13900/overview/, especially before summer time.

Has anyone else run into this?

[Clyde65]

That’s what I would go with. Should cool
It nicely!

[YoungPup1977]

Do you know if you have a Trans Temp Control unit which should have a bypass as well...? A good temp for the 6L80 is around 200 degrees.

[sweetk30]

these newer trans take dex 6 also . full synthetic .

and are you getting lockup in the convertor ? if not then this can create a TON of heat .

and if you live in cold area's its best to pass threw the rad to warm up the fluid faster but cool down after .

as said there is flow control valves that open/close ports at temp to help get warm faster and stay cool as needed .

[87Skier]

Originally Posted by YoungPup1977

Do you know if you have a Trans Temp Control unit which should have a bypass as well...? A good temp for the 6L80 is around 200 degrees.

Unless it is internal to the transmission, I don't have one. My plan was to run the fluid through the radiator, then through the cooler with the fan. I was going to buy an adjustable fan controller so that when the transmission fluid goes over ~210, the fan comes on until the temp is below 200.

It is running Dex VI fluid. Not too worried about cold temps. It mostly sees 40-80 F weather. Occasionally down to 10 and up to 100, but not often around here.

TCC lockup is only active in 4th-6th. I do very little driving in 1st-3rd. TCC definitely works.

[YoungPup1977]

Originally Posted by 87Skier

Unless it is internal to the transmission, I don't have one. My plan was to run the fluid through the radiator, then through the cooler with the fan. I was going to buy an adjustable fan controller so that when the transmission fluid goes over ~210, the fan comes on until the temp is below 200.

It is running Dex VI fluid. Not too worried about cold temps. It mostly sees 40-80 F weather. Occasionally down to 10 and up to 100, but not often around here.

TCC lockup is only active in 4th-6th. I do very little driving in 1st-3rd. TCC definitely works.

What Torque convertor are you running ?

[87Skier]

Originally Posted by YoungPup1977

What Torque convertor are you running ?

It's a reman stock torque converter. The only upgrade in it is a kevlar clutch.

[sprint_9]

A couple things to look into. What size are your cooling lines, stock 6l80 is 3/8 and stock th350 is 5/16. If your using the old 5/16 lines it might make a difference going to 3/8. The other thing I could think of is if you changed or have the flow right through the cooling system. So for example you want hot fluid leaving the transmission to enter the bottom of the radiator, and then exit the top of the radiator to your cooler, and then the same on the cooler, in the bottom out the top.

[87Skier]

Originally Posted by sprint_9

A couple things to look into. What size are your cooling lines, stock 6l80 is 3/8 and stock th350 is 5/16. If your using the old 5/16 lines it might make a difference going to 3/8. The other thing I could think of is if you changed or have the flow right through the cooling system. So for example you want hot fluid leaving the transmission to enter the bottom of the radiator, and then exit the top of the radiator to your cooler, and then the same on the cooler, in the bottom out the top.

It was setup correctly. I had it running PUMPED line to lower radiator. Upper radiator to lower cooler hose. Upper cooler hose to transmission RETURN.

My radiator is only 5/16", so I used 3/8" hardline where i could, but eventually it gets stepped down.

If I had to venture a guess on what is actually happening I would say it is a combination of several factors. First, I'm running electric fans. In the E38 ECM, the minimum temperature that you can set the fans to come on without running continuously is about 192 F. This is engine coolant temp and not radiator temp, so the radiator is probably getting close to 190 F (on the cool side) before the fans kick on. So if the ATF is at 205 and the radiator at 190, not much cooling is going to happen.

Second, the 6L90E in the stock vehicle also uses a air-to-fluid cooler that have a high density of cooling fins compared to the standard style coolers. I was using an undersized one, which definitely didn't help.

Third, there may be something going on with the transmission tune. Currently it is set up to have zero tcc slip at highway speed with low engine load. The default programming is setup to slip around 10 rpm at highway speed and never uses full TCC lock. This may be related to managing the PWM solenoid to the TCC. Forcing lockup may cause the TCC solenoid to be overworked.

Fourth, I have a NP205 behind it running gear oil with dual exhaust. NP205's tend to run hot, over 200 is normal according to forums and other sources online. Anything using a 6L90 would have had a chain driven ATF transfer case, with much lower mass. This all adds up to the transmission absorbing more heat from the surrounding components than the stock design.

This last point is inline with what I see when I log drives. The transmission starts off at a normal temperature, and slowly creeps up overtime. Usually around 1 hour, the transmission will get to 180+.

I'm not entirely concerned about it at this point. I just installed a Derale external cooler with a 10" fan. It has a built in thermostat set to come one at 180 F, and turn off at 165 F.

[DieselSJ]

For external coolers, you want it going through the external cooler FIRST, then through the radiator.

Several reasons -
First, you are removing a bunch of heat before putting the hot fluid into the cold side of your radiator. This takes stress off the radiator. Why would you want to heat the cold side of your radiator more than necessary?

Second, it helps the trans warm up faster in the winter, as well as helping it stay above 180. Contrary to popular belief, you can overcool a transmission. You want your trans to run between 180-200 degrees.

Trans > External Cooler > Radiator > Trans

I got this from trans guru Art Carr himself when he was building the transmissions for our desert racers. He plumbed all of our chase trucks that way.