6.6 6spd towing..some real world data.

Another JR · January 22

Yes the gas truck with the 6L90 has an auxiliary transmission cooler (air/oil heat exchanger) in front of the radiator near the bottom.

https://www.gmpartsdirect.com/oem-parts/gm-automatic-transmission-auxiliary-oil-cooler-23395755?c=bD0xJm49U2VhcmNoIFJlc3VsdHMmYT1nbWMmbz1zaWVycmEtMzUwMC1oZCZ5PTIwMjEmdD1zbHQmZT02LTZsLXY4LWdhcw%3D%3D

GMC4Zee · February 26

I will wait till someone posts a youTube video on how to do it. Mine runs about 205 when towing my 12K 5th wheel.

cbaker879 · June 10

Hello all,

I'm new here and new to the L8T 2500hd crew. We just took our first trip with our 10k 5th wheel trailer. With my previous gasser I could pull the trailer in 5th (6spd trans) gear without engine coolant temps rising.

With the L8T it runs at 210 unloaded and loaded running in 4th. But when I let it shift into 5th also a (6spd trans) the temp immediately jumps up to about 230 or so. If I manually shift it back to 4th it immediately drops back to the 210 mark. Is this normal? Or should I be having my dealership take a look at it

lineman1234 · June 11

Others have posted that it is normal, it is normal for my 2024.

Edited June 11 by lineman1234
better

cbaker879 · June 11

Yea, I tried to delete the 2 comments, wouldn't let me.

It just worries me that the temperature climbs 20-25 degrees within 1 mile after shifting into 5th.

Sitting in the upper half on a Guage on a truck that's supposed to be designed for much more weight concerns me after only 45minutes of driving. When a 5.3l never batted an eye at the same weight for hours on end in the same gear with a 3.42 rearend..

I moved to the 2500 just for the Payload assurance. Now I'm not so sure..

lineman1234 · June 11

Mine sits at 220 empty, so 230 wouldnt be much more towing. When i say 220 it is that way without a winter front cover in -10f or colder, in the winter after it warms up.

cbaker879 · June 11

I will see what it does the next time I tow the camper, just seeing it rise that fast worries me is all. Unloaded mine does not go above the 210 middle mark, and in 4th it stays steady at the 210 middle mark while towing. It was almost to the 3/4 line mark which marks 235 degree mark within a mile of shifting to 5th

Another JR · June 11

On 2/26/2024 at 2:43 PM, GMC4Zee said:

I will wait till someone posts a youTube video on how to do it. Mine runs about 205 when towing my 12K 5th wheel.

This message sounds like you understood my message to be about an optional add-on transmission cooler. I was describing the basic auxiliary transmission cooler that is on all the gas/6L90 trucks. It is called auxiliary because it supplements the primary cooler in the engine radiator.

cbaker879 · June 11

I'm not talking about trans temp, my trans temp stays consistent at 190 when towing. This is engine coolant temp I'm worried about.

Homewrecker007 · June 11

46 minutes ago, cbaker879 said:

I'm not talking about trans temp, my trans temp stays consistent at 190 when towing. This is engine coolant temp I'm worried about.

You can run a cooler temp thermostat. You can go down to 170° without retuning the ecm.

mrjulian416 · June 11

230 deg engine coolant temp seems very high even when towing. The cooling package should be able to keep temps around the 210 mark unless you are in very high ambient temps and pulling long hills.

cbaker879 · June 11

That's what my thoughts are, and why does it only climb when in 5th. Unless there is something wrong with the WP, or there's an air bubble in the loop somewhere.

I know the WP is mechanical based off the front pulleys, and I don't think 600rpm would make that much of a difference in cooling power