Transmission temperature on GMC Denali 3500HD 2021

[Dave Pelletier]

Originally Posted by jacknife

I would be suspect . A heavy duty transmission pulling an empty truck around should never get up to 255 . Did l not read that the high temp alarm went off ? They may have not filled it properly .

Sorry, I read that (perhaps too quickly) that he was towing his 5er. My point was only that temps in that range are somewhat normal for these new trucks, usage dependent, unlike what we are used to on previous models.

Cheers,
Dave

[Dave Pelletier]

Current thread on the Superduty page; 195 - 205 degrees empty diesel; 215 - 220 empty gas. Towing 15k up a grade; 230 - 240.....anything under 250 deg is said to be normal.

2 cents,
Dave

[spock12]

Originally Posted by jacknife

I would be suspect . A heavy duty transmission pulling an empty truck around should never get up to 255 . Did l not read that the high temp alarm went off ? They may have not filled it properly .

When I first talked to the technician he told me that the fluid needed to be replaced every 50,000 miles but when I was paying the bill he told me that I would not need the transmission fluid changed until I had 195,000 miles on the truck. I read somewhere that the transmission temperature getting to 260 degrees that the temperature would break down the fluid but it would take about 6,000 miles to do it. The transmission bumps a little now not all the time but occasionally. A female technician told me that the fluid should not be changed for at least a 100,000 miles but I guess the man was trying to make some easy money off me. They did a injector cleaning which was not needed, over $200 bucks plus I told them the front end was pulling to the left and was charged a 100 bucks just to check it, not fix it. I complained about it but it was like peeing in the ocean. I’ll take the truck somewhere else for service work. I change the oil and fuel filter myself

[xc-mark]

GM suggested 50K service in my owners manual. 195,000 I dont agree with at all. I have change my own fluids for years , if you see what the rear end and T case fluid looks like at 5000 miles you will never listen to someone telling you 195K is OK.

[TB673]

Originally Posted by theoldwizard

Excellent ! Although, it the trans cooler is plumbed into the radiator (like most are) is is hard to believe the temp is LESS than the engine coolant temp which is typically 180-190F.

Now granted, I'm going by the dashboard gauges, but the Engine temp is a constant 210 deg. whether towing or empty, flat land or mountains, 45 deg. ambient or 85+ degrees.
The trans temp will vary, but I've never seen it above 185 degrees.
A scan gauge most likely would deliver more accurate readings.


Tim

[spock12]

When I was coming home from the dealership not pulling anything the transmission temperature went to 260 degrees, the alarm went off at 255 degrees but by time I got off the highway the transmission went to 260 degrees. I took a short trip this past weekend and going to the campground about 75 miles the transmission temperature got to 139 degrees but coming home the transmission got to 234 degrees. I’m taking the truck back to the dealership Monday morning. I think that the technician that changed the transmission fluid didn’t know what he was doing. I took my wife’s Mercedes to same dealership, they sell GMC and Mercedes. They didn’t put enough oil in the car because the check oil light came on.

[rblanch]

Have a 2020 GMC 3500 with duramax and 10 speed trans. temps according to my Banks idash daily driving engine temp never above 185. engine oil temp 190, trans temp never seen above 160 mostly around 150. towing 20,000gvw toy hauler above 95degrees flat engine coolant 200, engine oil 210, trans temp 180. towing in mountains temps above 95 engine coolant temp 200 engine oil 217 trans temp 200. the only time i ever saw my trans above 200 was towing in Denver last summer stuck in traffic going up 6 percent grade for 10 miles constant starting and stopping without the torque converter locking it got up to 220 but went right back down to 200 after we started driving again.

[spock12]

What I think what the dealership should have done after the transmission temperature went to 260 degrees coming home from the dealership was replace the fluid. I read somewhere that once the fluid gets to hot the fluid starts to break down, lose its proprietary parts But I’m thinking the transmission temperature goes up the more I drive the truck. Now the temperature goes to 159 degrees just going short distances. Before this started the most I saw the temperature at was around town was 139 degrees. Sometime next month I plan on going to Sevierville TN for a few days and I normally run Black Mountain on I-40 and I’ll see what happens. We are planning a trip to Yellowstone this summer and I can’t have transmission trouble. The truck has 51,000 miles and is still under warranty plus

[jimcumminsw]

Where is the transmission temperature gauge reading from? Is this the gauge in the dash or displayed on an information screen?

The reason I ask is most of these gauges are not real gauges at all but what the ECM/PCM is telling you what it thinks is happening.

I have an actual gauge with a temperature probe in my transmission sump and my readings when towing is usually around 195F in the mountains sometimes going to 200F. Fluid and filters are changed every 50,000 miles or so.

I know my truck is older, a 2008, 6.7L Cummins (60HP/120lb-ft over stock) with the 68RFE- 6 speed auto that has a MAG-HYTEC oil pan which adds 3 QRTS more transmission fluid. With 3:73 gears, 4X4 pulling a 2016 34RL Cedar Creek. My usual highway speed is 65MPH in 6th gear about 1,600 engine RPM. In the mountains I am usual in 5th gear doing 55MPH at 1900 to 2000 engine RPM.

But I have never seen that high of a temperature reading in any of my trucks. 5 trucks now and they all had actual gauges installed on them. I have been towing camping trailers since 1973, all over the US.