2008 Suburban - Towing and Transmission Heat

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by augmont, Aug 1, 2012.

  1. augmont

    augmont New Member


    Newbie when it comes to towing. Our family just went on our 1st camping with our 2008 Suburban pulling a lite hybrid trailer (est. 5,000 lbs loaded). We live in Central California (near Fresno, CA) and we drove into the Sierra National Forest on Highway 168. The area that we go to (Wishon Dam/Courtright) is a favorite of our family and we camp there 2-3 times a year.

    Anyway, Highway 168 has a steep climb for about 2-3 miles and I was paying attention to the transmission temperature all the way up since i knew it was the steepest part of the drive. I had tranny temperatures near 240 degrees for during this stretch only. I was very concerned about the tranny temperature but not knowing if it would cause immediate or long term damage.

    I'd like to know when it makes sense to install a transmission cooler for towing. What's the max. temperature should i know when to pull over and let it cool? Is 240 degrees for a couple of miles OK or WAY too hot for the tranny? Also, what's my towing max?

    We plan on taking a trip in June 2013 to Mt. Rushmore and to the Grand Canyon later this fall and i want to make sure i'm prepared for our trips and that our suburban can handle it.


    P.S.......here's my VIN: 1GNFC16J18J219568 if that helps out.
  2. Conlan Rose

    Conlan Rose Epic Member 5+ Years 1000 Posts

    Ok, you prob should install an aux cooler because those are fairly high temps. Your max towing is 8,100 with weight distributing hitch.
  3. bazar01

    bazar01 Rockstar 100 Posts

    GM recommends 270F as the maximun ATF temp where you should be concerned. If it was my suburban, I will not take the risk. If my ATF temp gets up to 225F, I will slow down or pull over to cool it down to 200F. If it ever gets up to 240F, I will definitely stop and let it idle to cool it down.
    If you did not stop, I would install an aux ATF cooler and change the ATF to a really good synthetic brand just to be safe for the next trip.
  4. augmont

    augmont New Member

    thanks bazar01 and Conlan Rose.

    So i can better understand what i'm doing when towing up hill, would a lower gear (i shifted in 3rd gear in "tow/haul" mode on) and slower speed would have helped to keep the transmission cool. I'm thinking now that i was trying to go up too fast. I believe was doing 35 mph and i know it wouldn't go any faster.
  5. augmont

    augmont New Member

    I have a 3.73 axel on a 5.3 liter. Manual says 7,100 GWR but is that wrong? I reference the 5300 V8(Extended Models) 3.73 7,100 lbs (3 220 kg)
    Last edited: Aug 1, 2012
  6. Conlan Rose

    Conlan Rose Epic Member 5+ Years 1000 Posts

    Well I put your VIN# in a online decoder it said you have the 6.0, but yah if you have the 5.3 it is probably less. Also it doesn't really matter what gear your in lower gear just equal more torque all that weight is still on the transmission so it will still reach high temps. The best idea is a cooler to lower your transmission temps.

    You are right 5.3 has 7100 capacity weight distributing. I find that funny because my Tahoe has about 6,500 weight distributing with the current 3.42 gears it has, with the 3.73 it would have about 7,000.
    Last edited: Aug 1, 2012
  7. augmont

    augmont New Member

    Which on-line decoder do you use? I used this one http://www.compnine.com/vid.php?vin=1GNFC16J18J219568&x=0&y=0. It gives an RPO code of LY5.

    99'HEARTBEAT MODERATOR Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    With your Transmission running at 240 Degrees, you would like to see the Transmission Temps running in the Range of 150-200 Degrees When Towing,

    Having the Factory Tow Package, your Suburban does Have a Transmission Cooler (A Small one) going with a Larger Aftermarket Transmission Cooler, would be One Item to look at, to Help with reducing your Transmission Temps when Towing........the below link, is about doing a Transmission Cooler Swap and going with a Larger Aftermarket Transmission Cooler,

    Using the Tow Haul Feature is another way of helping Keep Transmission Temps Down, so the Transmission is Not Surfing/Hunting for what gear it wants to be in..........once again the below link, expresses on How and/or When the Tow Haul should be used when Towing,
    ***Link, Reply Number #3

    This Chart shows How Transmission Fluid Temps, can Affect the Life of Auto Transmission's,

    Last edited: Aug 1, 2012
  9. augmont

    augmont New Member

    It appears that i over estimated my GWR on the trailer (i can't find that' sticker anywhere. i looked in all the cabinet doors). It's probably no more that 3,500 lbs (dry weight is 2,760 lbs on nadaguides.com)

    With it being this light, i wouldn't think it wouldn't get that hot unless i'm not driving it correctly. thoughts?
    Last edited: Aug 1, 2012
  10. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Thank you for clarifying the weight, I didn't think a lite trailer would weigh that much.

    Your transmission temps are very high. Ideally, they should never exceed the engine water temps.

    You need a trans cooler, but first check to ensure there is not one on the truck. The build code of the heavy duty cooler package, is KNP, check the label on the glove box door to see if the code id there.

    No code, you should add a cooler.

    As far as driving is concerned, we have the tow/haul mode switch for that very reason. Use the switch when your in hilly country. If not so hilly, I use the manual selection and keep the trans in 5th gear, when I reach a hill, I manually downshift to 4th, top of hill, I manually upshift to 5th.

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