# Transmission Cooling Advice



## thefulminator (Aug 8, 2007)

I own a 2009 Silverado 1500. When I purchased it, I configured it specifically for the highest available towing capacity. When I tow, the truck is almost always over the 7,000 lb gross weight of the truck by about 800 lbs. I know I shouldn't do this but at the moment this is what I have to do. Getting another truck isn't an option right now.

The bumper pull tow rating on this truck is 9.500 lbs. I know some of you won't believe this so I have attached the supporting documents if you wish to browse them. The GCVW for the truck is 15,000 lbs. My 21RS has a 6,500 lb gross weight and from various trips through scales, I have never seen it over 5,450 lbs.

Last Sunday I towed the truck and trailer nearly fully loaded from Eugene Oregon to Lynnwood Washington straight through. In the Eugene area it was 95 degrees and I was driving at 65 mph. During that time the highest transmission temperature was 220 degrees.

My problem is that when I tow mountain passes the transmission gets way too hot in my opinion. The last couple times I pulled the rig over Steven's Pass, I was hitting 270 degrees. Both my Chevy dealer and customer service at GM says 270 is alright but I don't believe it. I stopped in at a local transmission specialty shop and they said that 270 is too hot. They said that it should be more like 220.

I think the problem is either lack of air flow when I am pulling up a grade or insufficient oil cooler size. It seems to me that I could have a larger cooler installed or add a fan to the existing cooler. The stock cooler is about 4.5" x 11" x 3/4". The transmission shop suggests that I both install a larger cooler and start using Amsoil transmission fluid at a cost of $690.

I'm looking for opinions as to what would be the best way to go. I don't know how much smoke the transmission shop is blowing at me. The truck is almost three years old and it just rolled over 20k miles.


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## Herbicidal (Aug 29, 2003)

I'd suggest talking to these guys for a second opinion: Import Performance Transmissions. Don't let 'Import' in their name fool you. I bought a larger tranny cooler and an in-line filter from IPT when I had my 2001 Tundra. I also switched to Amsoil for that truck, but I'm having a hard time believing it's that expensive! Maybe for the entire job including the fluid, cooler and labor? Times may have changed. Get a second and maybe third opinion. Anyway, these guys are the real deal and VERY knowledgeable. I believe a phone call is best for your questions and to hear their recommendations. If I were you, I would buy the largest tranny cooler that would fit in the space you have. Make sure the new cooler has a thermostatically controlled valve which I believe most, if not all of IPT's coolers have.

I also added a thermostatically controlled fan that mounted to the larger tranny cooler. I bought the fan from SummitRacing.com. Basically the fan helped in low speed situations, like when I was off-roading. Driving on the trails was slow going and not alot of air was moving over the tranny cooler. I don't think a fan would be very beneficial at highway speeds however. Tranny's are very expensive and heat is the biggest enemy, so it may well be worth the cost of those upgrades to ensure a long tranny life.


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## thefulminator (Aug 8, 2007)

Highway speed for towing both over Steven's and Snoqualmie passes is going to be 35-40 at the summits. That is one reason I thought a fan might do some good.


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## MJRey (Jan 21, 2005)

I agree that 270 is too high. High fluid temps can quickly kill a transmission. Synthetic fluid would help but you should check what you have now as many transmission fluids are synthetic now. You may already be running a synthetic fluid and you don't really need to spend the extra for the Amsoil at this time. Your first task should be to get the temp down and you have a few options.

- Add a larger cooler and they cost well under $100.
- Add a fan to the current cooler or the new cooler. Probably a good idea given the slower towing speed.
- Add a larger finned aluminum transmission pan to give more fluid capacity and provide some more cooling.

Personally I would go with a larger cooler with a fan, something like this: http://www.summitracing.com/parts/DER-13950/?rtype=10

I'd be willing to bet that someone already makes a kit specific to your model truck. You'll just have to do some searching to find the right one. After the cooler is on then I'd go with larger transmission pan. There are several brands to choose from such as Mag-Hytec, ATS, AFE, and many others. These cost between $200 and $300 and are fairly easy to install. I would do both of these before going with the Amsoil. Once you get the temperature under control then you can decide if the Amsoil is the right choice for you.


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## H2oSprayer (Aug 5, 2006)

Don't forget that the hotter the oil gets, the quicker it breaks down.


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## wolverine (Mar 5, 2009)

You could add a 2nd transmission cooler to the frame rail. My cousin had 2 of them mounted on his 1500HD. He used to get hot going slow up a mountain also. When I was crossing the Big Horn Mountains on my way to Yellowstone a month ago, my temp got up to 260 for a short time while I was going slow up a steep grade. Other than that my tranny ran in the normal range.


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## thefulminator (Aug 8, 2007)

Have been talking to a friend who is really into Silverados. He has had three in the past eight years. Stated with a 1500. Went to a 2500 HD gas then to a 2500 HD Duramax. He is telling me that with the Dexron VI fluid, this kind of temperature isn't unusual when towing up grade. He also says that from experience, he knows that the computer will put the truck into a reduced power "limp mode" if the tranny temp gets higher than the programmed max temperature. For now I'm not sweating it as much. May still add a fan to the cooler in the future just for peace of mind.


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## Collinsfam_WY (Nov 9, 2006)

I added "small-ish" dual trans coolers to my old F150. It did not come with one stock. The better coolers that folks here suggested were the "Long-Tru Cool" type. They do not produce a pressure drop I believe was one of the main reasons to use them. I simply used two coolers in-line that look something like these in the following link and I was good to go. Never had trans temps over 210-220 when climbing repeated hills albeit they were measured in the line just before the coolers. It has been a while but I think I paid something like $200 installed including the trans temp sending unit.

Tube-Fin Trans Fluid Coolers

-CC


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## MJRey (Jan 21, 2005)

I did a quick search on Dexron VI and I can't figure out if the specification means they are all synthetic or you have to specifically get one that is. In any case I would say that 270 is too high and some type of additional cooling would be a good idea for long transmission life.


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## Herbicidal (Aug 29, 2003)

I gave some more thought to just adding a fan. I honestly would not recommend that as a first step. Since you're going 35-40 mph at the summit, you would have to have a tranny cooler fan pushing air _*faster*_ than 40 mph to gain any benefit at all. I don't believe those small fans will put out a 50+ mph wind storm.

Anyway, my suggestion goes back to and as others have said, a larger cooler, either as a replacement or add in-line to the existing cooler. Doubling the cooling capacity will be far more effective than adding a fan. I bought the Long-Tru Cool one from IPT. In my experience on my old Tundra, the tranny cooler fan worked great for stop and go situations where there was almost no air movement. I set the thermostatically controlled, adjustable temp controller to activate the fan at 180 degrees. Worked great, but again, in stop and go traffic or while 4 wheelin' on the trails where my speed was like 5 - 10 mph. So, there's my advice.


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## thefulminator (Aug 8, 2007)

The fan I am looking at is a puller not a pusher. In effect it draws a vacuum on the back side of the cooler creating a pressure differential across the fins. More pressure differential equals more air flow. I've done the calcs and at zero resistance the fan blows at a little over 20 mph. In any case it won't hurt to have it.


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## RDS (Jul 20, 2011)

All you need is a larger cooler. At 35-45 mph a fan will not do much at all. (would help sitting in traffic)

I installed a cooler on my truck made by Earls it is 14"X 8" and almost 2" deep. My trans has never gone over 200.

The cooler comes with AN fittings that will come out and the factory fittings will screw in. All I had to do was make some brackets to mount it.

The cooler with the ? mark in your picture is a power steering cooler.

Dex 6 is synthetic.


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## TeleRomeo (Aug 19, 2012)

Not that is mattered. In your picture Radiator 2 is an ac condenser and the ? is a power steering cooler.

Get the largest cooler available from hayden. That should do the trick for your cooling concern.


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## thefulminator (Aug 8, 2007)

Pulled the trailer over Stevens Pass yesterday. For the first time I put the truck in manual (M3) when leaving Skykomish at the bottom of the hill. This time it maxed out at 234 degrees. Guess I will be using manual for passes in the future.


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## CamperAndy (Aug 26, 2004)

Sorry for getting to the party late but i was just going to say that your torque converter is unlocked in the conditions you described and that will really jack the temps up. Short runs at 260 - 270 will not kill anything with the current oil formulas but may need the coolant replaced more often.

So anything that will put you in a locked converter mode will help significantly. It looks like you found the answer by putting it in manual mode.


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## Lmbevard (Mar 18, 2006)

thefulminator said:


> Have been talking to a friend who is really into Silverados. He has had three in the past eight years. Stated with a 1500. Went to a 2500 HD gas then to a 2500 HD Duramax. He is telling me that with the Dexron VI fluid, this kind of temperature isn't unusual when towing up grade. He also says that from experience, he knows that the computer will put the truck into a reduced power "limp mode" if the tranny temp gets higher than the programmed max temperature. For now I'm not sweating it as much. May still add a fan to the cooler in the future just for peace of mind.


Personally, I would still think about adding an external transmission cooler. They are added in front of the radiator so that engine heat doesn't come into play so the transmission stays cool. Even with synthetic fluid, other parts can break down at the higher temperature. I had my transmission on my Dodge go south on me and ended up paying $3300 to get it fixed right. If your going to be pulling the mountains often, it would pay to add the cooler. The guys that did my transmission build up truck racing transmission so I trusted his opinion. Good luck with the truck.


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## thefulminator (Aug 8, 2007)

I already have a factory installed external cooler mounted in front of the radiator. I didn't know that towing in M vs. D would lock the torque converter and create less heat. The owners manual doesn't say anything about that. It just says you can tow in D or M but doesn't give much of an explanation.


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## CamperAndy (Aug 26, 2004)

thefulminator said:


> I already have a factory installed external cooler mounted in front of the radiator. I didn't know that towing in M vs. D would lock the torque converter and create less heat. The owners manual doesn't say anything about that. It just says you can tow in D or M but doesn't give much of an explanation.


Owner manuals do seem to really lack in details. Just playing with my truck I found out things I did not see in the manual. One of them was that if I put the truck in "2" the torque converter will lock up at about 25 mph when in tow mode. Normally it will not lock in 2nd gear at all. This really helps when pulling out of a campground with a steep climb out of a valley to the main road where you can't build up much speed. Really helps keep the temps in check.

The above may not apply to your truck but to the Dodge owners it could be helpful information.


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