GMC / Chev. Question - Montana Owners Club

abonzer · 08-01-2008, 10:04 AM

I have some questions that I would like to see where other GMC / Chev owners are at. The truck is 2500HD
Question:
What trans temp do you show when normally towing?
When towing, what tire pressures do you run in your tow vehicle?
Lastly for those with air springs. What pressure do you run and what is your pin weight. I am trying to find the best pressure to run. My pin weight is 2,100 lbs according to the book.
Thanks in advance!

bigred715 · 08-01-2008, 12:21 PM

Your temperature depends on a lot of things . I tow a 2880RL weighing about 10600# and normally with outside temp about 80 degrees I'm at about 190 to 200. Coming off a long hill it will go down to about 170. I tow at about 60mph.
I run 80# air in the rear of the truck and about 75# in the front. In the trailer I reun 80#.
Don't go by the pin weight in the book or brochure because those figures are really light. Take your rig to the scale and find out for sure.

8.1al · 08-01-2008, 01:39 PM

We are fulltimers and our 3575 weighs 13,600 and the pin weight is 2800 lbs. When towing I run 80psi in the rear and 50 in the front. Don't need anymore in the front because it never gets that heavy so why beat yourself to death? We have airlift airbags on the rear of our 2500HD and I run them 45-50psi.

dsprik · 08-01-2008, 02:42 PM

My 2002 GMC 2500HD Duramax w/ 5sp Allison runs 190°-195° when towing. If it hits 210°, bad things start to happen. Water temp will spike (not over red, though) and the oil press drops.

I have Michelin LTX M/S and run what the door panel says to run. 55# on front and 80# on rear.

I have Airlift airbags (w/ my 4x4 suspension) and I run them @ 55# with a pin weight of ~2,300# on my 3400.

Hope this helps.

*On Edit~ I also run 62-63 mph @ 19.5K RPM, always Tow Haul with the Monty.

Steve and Brenda · 08-01-2008, 03:30 PM

I'm the same as Charlie. Red, why keep the front tires so high when the required pressure is 55 PSI?

HughM · 08-01-2008, 04:33 PM

I've never seen 195 temp for the tranny. Mostly 180-185 but I live in Florida and don't usually climb 8,000 ft mts. I do however tow in hot tempertures and still it doesn't go over 185.
Front tires are 60 and rear 80 lbs. that's what the door sticker calls for.
No air bags for me.
Hugh

dsprik · 08-01-2008, 05:05 PM

Quote:

quote:Originally posted by HughM

I've never seen 195 temp for the tranny. Mostly 180-185 but I live in Florida and don't usually climb 8,000 ft mts. I do however tow in hot tempertures and still it doesn't go over 185.
Front tires are 60 and rear 80 lbs. that's what the door sticker calls for.
No air bags for me.
Hugh

Hugh, my Allison is the 5 speed trns. Yours is the new 6 speed. That may be the difference. Wish I had the new 6 speed, but then I would have to wrap a new (or almost new - 2006+) GMC truck around it... Costly way to go to get that extra gear.

Also I am curious about the 60# reading on your door post for the front tires. Apparently GM changed this from 55# for some reason??? And when did they do this?

abonzer · 08-01-2008, 05:06 PM

Follow Up question- It seems most run 80 in the back. Is that 80 with the 5er hooed up or unloaded. I would imagine that 80 unloaded would increase once the trailer is hooked up and the weight is on the tires.
Thanks again in advance!

dsprik · 08-01-2008, 05:10 PM

Quote:

quote:Originally posted by abonzer

Follow Up question- It seems most run 80 in the back. Is that 80 with the 5er hooed up or unloaded. I would imagine that 80 unloaded would increase once the trailer is hooked up and the weight is on the tires.
Thanks again in advance!

Ideally: Empty, ambient temp at 72°, @ sea level. AND a good, accurate gauge - many aren't.

Snownyet · 08-02-2008, 03:31 AM

Early duramaxes had undersized cooling systems and overheating was and is not an uncommon occurence when conditions are right, the transmission really has nothing to do with it. The newer LLY and LBZ trucks dont typically suffer from the same problem and for what its worth, even with the new duramaxes if you tow like we do avoid aftermarket grilles, most do cut airflow. I trypically dont see over 200 deg on the trans temp unless its a loooong uphill pull, I tow with 60psi in the front and 80 in the rear, run 20 lbs in my firestone bags(measured with the truck unloaded) and I believe my pin weight is an advertised 2250#.

mail2us · 08-02-2008, 05:04 AM

Our 2007.5 Chev Duramax has been over 200 temp. Our truck mechanic who also tows with a 2008 Duramax says the truck can easily handle the high temps when climbing. There are some elevations here in NC/TN that can increase the temp. Normal towing temp is about 165-170 on our TV which I think is LMM. The LB7 engine was replaced in 2003 with the LLY, then the LBZ and now the LMM diesel in 2007.5 Dennis

dsprik · 08-02-2008, 05:50 AM

My 2002 is a LB7. I thought about changing out my trans fluid to try to combat this temp spike, but I was told that you cannot change it all out at the same time? Only 6 or so qts out of the 22 qts? Have not checked with a dealership though on this. I do keep my spin on filter changed at regular intervals.

Also, still curious as to the change on the front tires (GM) from 55# to 60#. Was that a front suspension change after my 2002 2500HD or did GM just decide that 55# was too low???

mtheo · 08-02-2008, 10:13 AM

I run 55# in front and 80# in rear and about 30-40 in air bags, just enough to keep the truck level. As for running solo, 55# all around.

SlickWillie · 08-02-2008, 11:31 AM

Quote:

quote:Originally posted by dsprik

My 2002 is a LB7. I thought about changing out my trans fluid to try to combat this temp spike, but I was told that you cannot change it all out at the same time? Only 6 or so qts out of the 22 qts? Have not checked with a dealership though on this. I do keep my spin on filter changed at regular intervals.

Also, still curious as to the change on the front tires (GM) from 55# to 60#. Was that a front suspension change after my 2002 2500HD or did GM just decide that 55# was too low???

Perhaps it is a crew cab. My son's early 04 (LB7)calls for higher pressure in the front than my crew cab 04.

dsprik · 08-02-2008, 11:38 AM

Quote:

quote:Originally posted by SlickWillie

Quote:

quote:Originally posted by dsprik

My 2002 is a LB7. I thought about changing out my trans fluid to try to combat this temp spike, but I was told that you cannot change it all out at the same time? Only 6 or so qts out of the 22 qts? Have not checked with a dealership though on this. I do keep my spin on filter changed at regular intervals.

Also, still curious as to the change on the front tires (GM) from 55# to 60#. Was that a front suspension change after my 2002 2500HD or did GM just decide that 55# was too low???

Perhaps it is a crew cab. My son's early 04 (LB7)calls for higher pressure in the front than my crew cab 04.

I'm not sure, Will. I have an ext cab LB. Mine is an early 2002.

sreigle · 08-02-2008, 02:25 PM

I don't have the GM so can't reply to those questions. But I did want to suggest maybe those relating their tranny temps might tell us where the temp sender is located. I had third party gauges on two trucks (not GM). One had the sender in the transmission pan. The other had it in the line going from transmission to radiator/cooler. The pan temperatures are much lower and fluctuate more slowly than those in the line coming out of the transmission. The line coming out of the transmisstion to the cooler is where the transmission oil is hottest. So, it might be helpful to know both the temperature and where the sender is located.

Illini Trekker · 08-03-2008, 04:30 AM

My tire pressure is similar to others here with 1100# on rear axle and 45# increase on front axle. Temp close to other, AC will bring up trany temps. I put 12 to 14 pounds of air in my bags just enough to bring truck off the over loads.

KathyandDave · 08-04-2008, 08:54 AM

You said: I also run 62-63 mph @ 19.5K RPM, always Tow Haul with the Monty.
Did you mean 1.95K RPM? Why always Tow/Haul? It increases the RPM, which suggests that fuel consumption is increased. In our admittedly brief experience, on flat terrain, the ordinary gearing pulls well at lower RPMs. We're using the T/H only for grades and leaving it on for hilly terrain. Are we missing something?

KathyandDave · 08-04-2008, 09:04 AM

To mtheo: Looking at your rig, you've got a fair amount of weight on the back of the Montana. How is it supported and how have you accommodated the stresses of the bikes bouncing at the end of a long lever when the trailer wheels cross the inevitable bumps in the the road?

Snownyet · 08-04-2008, 09:08 AM

Quote:

quote:Originally posted by KathyandDave

You said: I also run 62-63 mph @ 19.5K RPM, always Tow Haul with the Monty.
Did you mean 1.95K RPM? Why always Tow/Haul? It increases the RPM, which suggests that fuel consumption is increased. In our admittedly brief experience, on flat terrain, the ordinary gearing pulls well at lower RPMs. We're using the T/H only for grades and leaving it on for hilly terrain. Are we missing something?

Tow haul increases the rpms that the transmission shifts at as you accelerate. When crusing down the road at 60 my rpms are the same in both tow haul and regular mode. Plus using tow haul activates the grade braking feature on newer trucks.

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