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Old 07-06-2016, 07:27 PM   #1
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Transmission Fluid Temperature-what is too hot

New to IRV2 and RVing. We have a 2000 GMC Sierra 1500 with 5.3l and standard 4 speed auto transmission. Truck is low mileage and well cared for. Towing a 2014 Lance TT 2285 and the factory says dry weight about 4500# with GVW at ~6500# but I am sure I never load it above 5500#. GM says truck should be able to haul 8-9000 lbs. (depending on what source you are looking at) but eventually I will want to have a larger safety margin than 3000-3500 lbs. I installed an instrument cluster out of a 2500HD because I wanted the transmission temperature gauge and it monitors the temperature from wherever the factory sensor is that feeds the Electronic Module/brain.

Moving down the road with no tow the transmission fluid never goes above 150-160 degrees. Towing the trailer on flat at 55-60MPH it can go all day and never rise above 175-180 degrees. Going up inclines for 10 minutes or more and fluid temperature goes up to 200-210 degrees. After a recent trip when the temperature hit 210 degrees I pulled the dipstick and fluid was still pink and did not smell burnt.

On a GM Discussion board I saw some debate and a few people saying that at 180 degrees the fluid begins to degrade and above 200 degrees it really degrades quickly. I have asked a couple of transmission repair people and they just kind of look at you with a blank stare because, I think, they are into repairing the tranny after you have burned it up and not really knowing much about the science behind the fluid and what is going on to prevent it. A search of the IRV2 pages found a really old discussion dominated by guys with very large tow vehicles pulling 12k and 14k rigs reporting temperatures similar to what I am seeing with one guy reporting 240 degrees on steep hills. The red zone on the gauge is 300 degrees but one commenter said, probably correctly, that if the temperature gets up there you have probably already toasted the tranny or at least the fluid.

So my question is: does any one here have expertise or knowledge about what are safe running temperatures for transmission fluid before it begins to rapidly degrade??? I have not found guidelines for when you should think about changing the tranny oil based on how hot and how long the fluid has been at various temperatures.... We are going across the country and back and I am wondering if I need to plan on changing transmission oil half way through the trip??
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Old 07-06-2016, 07:44 PM   #2
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If you are really concerned why dont you contact a GMC dealer or the manufacturer and get the facts? Personal opinions will probably get you a damaged transmission.
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Old 07-06-2016, 08:07 PM   #3
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This chart should assist you:

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Old 07-06-2016, 09:31 PM   #4
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Bear in mind that most if not all manufacture's cool the ATF routing it to heat exchangers in the main radiator side tanks. Very much like they do for engine oil (who monitors there oil temp?). They do this as it tends to help warm up those fluids in cold weather. Keep it cooler in hot. I'd expect the ATF temp to somewhat mimic the coolant temp. This with a lag or delay. Oils have slightly different heat transfer properties compared to water. They can function a higher temps but don't move and dissipate heat as effectively as water. They've been engineered to do their best work at the viscosities in these operating temp. ranges.
If ATF gets hot enough it will expand and spray out of the vent system and make a heck of a mess on the front of a trailer. (don't ask how I know that)
I follow the temps in tow / haul mode as most would as the DIC changes to transmission temp. I've also watched it using some real-time OBD2 interface apps.
Severe duties should merit severe service intervals and recommended fluids, but stay within the vehicles design limitations.
Use a CAT scale. Check it against the door frame sticker.
Ever check your differential temp. while towing? That rear-end chunk can get pretty warm too.

Happy motoring.
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Old 07-06-2016, 09:49 PM   #5
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You might also want to consider switching to synthetic tranny fluid. It can tolerate the heat better without breaking down. A very experienced and top notch Mopar transmission guy I know once explained it this way. After high temps the fluid will loose some or most of it's protective capability but still act as a pressure fluid. Things will still shift and move but with a lot more friction. I would add a larger 2nd cooler to help with the hard pulls and long hills. The Ram trucks can be upfitted with the larger cooler say from a 1 ton unit onto a 3/4 ton for better cooling. Lots of ways to handle the increased temps from hard pulling. Another is to add a drain plug to the tranny pan ( I did this with a fleet of police cars years back and we would drain and refill every ten thousand or so and never had a transmission problem) so you can drop several quarts and refill with fresh fluid.
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Old 07-07-2016, 06:25 AM   #6
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For the GM 4L60E and similar transmissions, the general rule of thumb has been to install a decent fluid cooler, and keep the temps below 200 degrees. GM recommends the Dexron VI fluid for anything that used Dexron III (except the T56) supposedly it's more stable and has a longer life. I can't say one way or the other, but I can say from experience that the 4L60E will be toast if you run it over 200+ degrees too long and too often. Once that fluid begins to break down, the clutch and band material goes with it. My 2009 Silverado's manual, in severe duty applications, it says to change the filter+pan fluid every 30-50K miles. Same with the rear differential and transfer case of you have one.

Keep the temps under 200 with a cooler, and change the filter/pan fluid regularly, only do the GM approved flushes if you have one done, and the transmission will be fine. I've got 130K miles on my 2009 now, at least 10-15K are hard towing (8000 lbs) still tows likes its brand new.

If you want to reduce stress on the transmission. Get the truck regeared. I'm currently running a 4.11 gear equivalent in mine.
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Old 07-07-2016, 07:02 AM   #7
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X2 on the second transmission cooler, I always add one. We almost always tow a car trailer and have never had an issue during 300,000 miles of use with the last three motorhomes. I currently use a scangauge and the tranny runs well under engine coolant temperature.

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Originally Posted by MagnaPilot View Post
For the GM 4L60E and similar transmissions, the general rule of thumb has been to install a decent fluid cooler, and keep the temps below 200 degrees. GM recommends the Dexron VI fluid for anything that used Dexron III (except the T56) supposedly it's more stable and has a longer life. I can't say one way or the other, but I can say from experience that the 4L60E will be toast if you run it over 200+ degrees too long and too often. Once that fluid begins to break down, the clutch and band material goes with it. My 2009 Silverado's manual, in severe duty applications, it says to change the filter+pan fluid every 30-50K miles. Same with the rear differential and transfer case of you have one.

Keep the temps under 200 with a cooler, and change the filter/pan fluid regularly, only do the GM approved flushes if you have one done, and the transmission will be fine. I've got 130K miles on my 2009 now, at least 10-15K are hard towing (8000 lbs) still tows likes its brand new.

If you want to reduce stress on the transmission. Get the truck regeared. I'm currently running a 4.11 gear equivalent in mine.
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Old 07-07-2016, 07:06 AM   #8
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Not a GMC but I added an extra transmission cooler to my F350 and it rarely gets over 125 degrees unless it's over 90* outside. Then it will run 150. Towing (9k load) usually adds 25* to whatever the unloaded temp is but have never been over 180.

The normal temps without the extra cooler was 180-200.
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Old 07-07-2016, 09:23 AM   #9
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Climbing steep hills, downshifting and backing out of the throttle will help your systems run cooler. Don't stop at the top and shut off your engine.
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Old 07-07-2016, 09:49 AM   #10
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X2 on the extra cooler and using sythetic ATF. Definately higher cost but well worth it IMO.

Check with a reliable tranny shop on what they would recommend for fluid.

If you change fluid make sure you also change the filter if it serviceable.
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Old 07-07-2016, 10:29 AM   #11
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DEXRON-VI Automatic Transmission Fluid is the only approved fluid for warranty repairs for GM transmissions requiring DEXRON-III or prior DEXRON transmission fluids.
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Old 07-07-2016, 10:44 AM   #12
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98 p30 chassis 130k miles with the L480 with trans oil cooler. When towing heavy total weight 15k lbs, flat I run 165, slight incline 180, up 8% hill 210-220, ambient temp 100. As a rebuilder, change your fluid every 25k, need it or not, heat kills the fluid. (don't worry about changing the torque converter fluid) Just drain and refill. That is the very best you can do for it. Like engine synthetics, if you have money to burn, go ahead, burn it. But in my experience it will not make your hydraulic pump last any longer. Sitting with out driving is the worst thing for a tranny, water vapor builds up in side the tranny and then problems start. If you drive the thing once per week then the water vapor gets burned off and all problems go away.

If you are running over 220 then you will need to deal with the temp. IE: run lower gears, slow down, increase tranny cooler size, lighten the load and heaven for bid, stop and give the thing a rest!
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Old 07-07-2016, 11:08 AM   #13
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Also, think about this. A 1/2 ton truck is designed to carry 1000lbs. You put a 5000lb trailer behind it, regardless of what it is rated at, you are going to get a hot engine, hot brakes, a hot tranny and so guess what? it will not last as long as if you were not towing. sounds like you are coming in at about 10klbs total, here is the part that doesn't make "chevy" sense. "truck should tow 8-9k lbs". How can a truck rated at a payload of 2k lbs tow a 5k trailer up a 8% grade? It can, at 20 mph in 1st! Try this at 50 and you will get the "ole exploding tranny" routine.

It is the "chassis" that is rated high, common sense has to figure out the rest. You are towing a heavy of a load with a 1500 1/2 ton, in my opinion, you are way over loaded, but so what?

Look at the horsepower in a semi compared to the tow weight, nothing wrong with your setup, just slow your down!!! and use your gears to keep it from over heating!!!
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Old 07-07-2016, 08:39 PM   #14
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Just for reference. Not knocking the Ford guys, but I know the newer, at least the 2011+ F-150's, read a much higher transmission temperature. I assume it's measured in a different location compared to how GM reads theirs. So a Ford to GM conversion isn't quite apples to apples for this purpose.

Just in case you get in a conversation with a Ford guy about the subject.
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