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Towing in a non-standard configuration

Discussion in 'GM Powertrain' started by Crawdaddy, Aug 10, 2011.

  1. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts

    Well, tommorow I'm going to be picking up a trailer that weighs around 3000 pounds. No big deal, except I'm still running in my slightly screwy transmission cooler setup. My 700R4 transmission is getting cooled only by an auxillary transmission cooler, and has been since I replaced the transmission. When I replaced the transmission, I pulled the radiator cooler out of the loop in a fit of being an idiot. I haven't had any issues with it, but this is the first moderately heavy trailer I'm pulling with the truck since then. So the question is, is my aux transmission cooler at least as good as the factory cooler that would be in the radiator? If so, I think I'll be fine towing this trailer as the specs for the truck list that there's no special options needed to tow up to 3000 pounds.\

    Also, could I/should I tow this trailer in overdrive? I am pulling the trailer around 4.5 hours one-way and overdrive would really help on fuel mileage if I don't burn the transmission up in the process? It seems like the trailer should be light enough not to cause an issue, but cooking a tranny is a VERY unattractive option.

  2. phoebeisis

    phoebeisis Active Member 1000 Posts

    I would pass on the overdrive.
    True it might get you another mpg-but not worth the risk
    I would guess at 60 mph towing in OD might get you 9-10 mpg vs 8-9 mpg

    Is your aux cooler sorta in the breeze-with a clear shot at incoming air- ?
    I would bet the aux cooler would work just fine- might even have more surface area than the stock setup.
    Of course there is a lot to be said for OEM setups-engineers usually know their business and the stock setups are usually pretty clean looking.
    I know the feeling of having an attack of "seemed like a good idea at the time" sorta thing.
    I wouldn't use the OD- aftermarket cooler should work ok.Temp gauge??
    How many RPMs does it turn in OD vs 3rd-maybe 1800 vs 2300 rpms?
  3. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts

    It's not a great pic, but it's all I have at the moment. This is a pic of the cooler behind the grill:

    And here's the whole thread on the install of the cooler:

    I'd say that when I'm on the highway (90% of the trip), it has plenty of breeze. I'm not sure of the RPM difference because the truck doesn't have a tach, but the overdrive gear in 700R4s is pretty steep, something like a .73 ratio vs the 1 for 3rd gear.
  4. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts

    Well, apparently the truck can tow that 3000 pound trailer with just the small auxillary cooler pictured. We towed in 3rd gear with an average speed of 55-65mph. At every fuel stop I checked the level, color, feel, and smell of the transmission fluid. The level stayed great the whole trip and the feel of the fluid was consistent. The fluid got a little less red and more transparent as time went on. It also started to smell less strong, but never picked up a burnt smell to it. Touching the exposed pipe bends of the cooler gave me between a 1.5 to 2 count before I had to remove my hand. No slipping was detected in the transmission while towing.

    That said, I'm now going to get the cooling system set up how I really want it, going into an external transmission fluid filter, going through the radiator cooler, then to the biggest B&M cooler available. I'm also going to do a fluid swap in the transmission and new filter, and possibly a new deeper transmission pan with a bung for a temp sensor.
  5. phoebeisis

    phoebeisis Active Member 1000 Posts

    What sort of mpg did you get?
    The cooler looked like it was maybe 8" by 12" ?? Decent sized, but the bigger the better in south louisiana/Miss. summers
    So you will set it up to be double cooled-OEM setup thru radiator then a big aftermarket one-with a way to measure temp?

    One to two seconds sounds fairly cool- bet that is under 200 degrees? 200 degree metal is plenty hot.
  6. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts

    I averaged 12-13 mpg. The trip out empty to pick the trailer up didn't yield the 15 mpg I got when driving it to work for a week, but I still consider the mpg good. The trailer was taller than the truck and had a front wall on it, so it had considerable wind drag.
  7. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts

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