Maximum tranny temp

tcfulmer · Jan 27, 2011

2009 Silverado 1500 crew cab 4x4 LT1
LC9 - Engine: 5.3L, V-8, Flex Fuel, SFI
MYC - Transmission, 6 Speed Auto
GU6: Rear Axle, 3.42 Ratio
Z82: Trailering Package
K5L: Heavy-Duty Cooling Equipment
KNP: Transmission Cooling System.

Was towing my trailer over Steven's Pass in Washington State which is pretty steep. The tranny temp was getting into the 250F range which made me ask a question. Just how hot can it get before I should start getting concerned? Called my dealer and they said 300F which is the temperature sensor limit. Does that sound right? Looking for opinions.

lzn197 · Jan 27, 2011

I personally have not experienced what you are going through but my memory tells me that when you achieve transmission temperatures of 235F or above, you SHOULD be concerned. If it is at all possible when you are driving and that occurs, you should slow the vehicle down for a mile or so then pull over and put the vehicle in park and let it idle and cool down. This may take several minutes. Here is why you should be concerned. The transmission fluid starts to break down at 235 and above. If you continue to use the vehicle with fluid that was subjected to such temperatures, you are putting your transmission in jeopardy. Get a complete fluid change as soon as possible and in the future, try to monitor the temp and do as stated above for cooling.

Hartski · Jan 27, 2011

Might want to get some different gears if you're going to be towing in the mountains much.

LBZDMAX · Jan 27, 2011

Might want to get a truck that can handle what you're towing. Especially over those passes.

If you start seeing anything over 220 for an extended period of time you should slow it down and let it cool off for the exact reasons Izn already stated above. Change your fluid and watch that temp from here on.

GMman · Jan 28, 2011

Wondering how much you were towing versus what you truck is rated for ?

katjar503 · Jan 29, 2011

If your didnt over load it you have a trans problem have it checked out.

gmctruckguy · Jan 30, 2011

"General Motors' in-house towing team expert provided RV Clinic with this statement: The maximum allowable automatic transmission fluid temperature is dictated by the transmission oil itself. The oil begins to degrade significantly above 270 degrees Fahrenheit, so we design vehicles so that in all but the most extreme conditions, the fluid temperature in the transmission sump stays below 270 degrees F.

We allow for up to 285 degrees F in extreme conditions (i.e. towing a trailer with combination loaded at GCWR in Death Valley). But for customer usage anywhere else in the country, even at GCWR, transmission sump temperature should stay well below 270 degrees F. Above this point, certain internal components, such as seals, begin to disintegrate rather quickly. Although newer synthetic fluids can withstand higher temperatures we still recommend this (270F) as a maximum temperature. "

aksierra11 · Jan 30, 2011

250 is way high. Heck I get concerned if it even gets close to 200

EKinMN · Jan 30, 2011

There seems to be a consensus here, somewhere in the 220-270 range. I had also read 235, mentioned earlier.
I think the real question to the OP is, what the heck are you towing? You have basically the same specs on your truck as I do, which are pretty robust for towing. Please share what you are towing, and what the conditions were that caused the tranny to heat up so much. Thanks!

tcfulmer · Jan 31, 2011

I was towing a 2008 Outback 21RS which has a shipping weight of 4565 lbs, gross weight of 6500 lbs and tongue weight of 375 lbs. I know I was no where near the gross weight since all the water, grey and black tanks were empty. It did have full propane tanks and was lightly packed for the outing. The truck wasn't loaded very heavily either.

I think the problem was the operator. It was the first time I had towed this trailer with this truck and I was still getting used to the way the tranny would shift on hills. I towed the same trailer with my 1999 Silverado LS extended cab 4x4 with 5.3L, 4 speed and 3.73 gears without a problem. The old truck had a 6500 lb towing capacity where the new one is 9500 lbs. I was towing up Steven's Pass on the West side and it took me a while to figure it out. Was just asking the question for future reference.

tcfulmer · Sep 2, 2011

Was towing the same trailer over I-90 Snoqualmie Pass last week. Weighed the trailer before hitting the hill. Trailer axles came it at 5240 lbs. Was pulling 60-65 mph up the hill until starting the final assault on the summit where it slowed to 40-45 mph. Tranny temp got to 243F. Dealer still says I don't need to worry unless it gets to 260-270F and that they think 240-250F is normal for towing over a mountain pass. Still wondering if there is some sort of problem with the truck. It's rated to tow almost twice that (9600 lbs). When on normal roads and not towing it stays around 190-195F. Was reading another thread about an older model with air diverter problems. Has anyone had any problems with the K5L heavy-duty cooling equipment?

LLAMA · Sep 2, 2011

try a to switch out fluid to AmsOil i hear that helps big time with temp

CKNSLS · Sep 2, 2011

I have the same truck but only 2WD, and almost the same trailer. I have a Shamrock 21RS (almost identical to the OPs-only it's made by Forest River). I had temperatures that said 400 degrees in the tranny , but never had any of the other warning systems come on. It was a 105 degree day pulling up a 17 mile grade to Lake Arrowhead in the San Bernardino mountains in So. Cal.

I am not sure what happened - it only has 6,000 miles on it. I inspected the fluid and it looked at smelled fine afterwards. I had a "old school" transmission shop who has been in business 20 years tell me there is no way I got that hot without my dash lighting up like a Christmas tree.

Don't want to hijack this thread - but I wanted to share my experience with the OP.

I suspect there is something going on with a few select trucks when towing - but I don't know what.

The truck has been to Utah and back to So Cal since this incident (not towing) and the truck performed great in 116 degree temps coming across the Nevada-California desert, with the tranny in the high 190s during what could be called extreme conditions.

I do plan on a drain and fill with Amsoil at about 30K. Also, at some point an aftermarket B&M cooler.

tcfulmer · Sep 2, 2011

I'm going to have the dealer look at it when I'm in for my next oil change. When I had the 250F, it was a 7.5% grade for 13 miles. The truck has less than 14,000 miles so I don't think the ATF has age problems. Perhaps the sensor is bad.

Maximum tranny temp

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