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tim1973's avatar
tim1973
Explorer
Nov 09, 2021

Transmission cooler options

Hi all, this is a good forum been following it for years as anonymous. This is a lil long, but hopefully yall dont mind. Anyway, looking for some thoughts from other RV'ers. I have a 2011 Denali Yukon 6.2, recently purchased a TT with 6400 dry weight and about 7200 loaded(checked weight on a scale) with about 650 tongue weight. When i first bought it, we brought it home which was about a 90 mile ride, some small hills etc. Noticed the engine temp got up to about 230ish and the transmission also got up to 225-230. I decided to update the cooling system and add a larger transmission cooler. Put the 40K cooler in place of the factory one, and replaced the water pump(AC delco), aluminum aftermarket radiator(With internal transmission and oil cooler, as the OE one had), new ac delco radiator hoses and tsat.

Took TT on a 4 hr trip, pretty much flat ground, and ambient about 80F. This time, transmission got up to about 140F, engine though, still was getting up to about 230 at times..then going back down to 215ish. So, I didnt like the trans not getting up to proper operating temp(With no trailer, its barely getting over 110F), so I decided to install a transmission thermostat/bypass. Got the tru-cool one. Heres where i wasnt sure what to do. I decided on installing the tstat before both of the coolers, allowing bypass until up to proper temp. i decided to have the fluid go to the external cooler first, then on to the radiator internal cooler, then back to transmission. Vs going to the radiator first, as the OE had. Ideas? Thanks!

My thinking is, this allows full advantage of the 40K external cooler, and will reduce the amount of heat being given to the radiator coolant...hopefully allowing engine to run a little cooler? So far ive driven vehicle about 45 minutes, with no trailer on it. Tranny fluid gets to 185 and so far stays perfect.
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  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Nov 09, 2021
    Interesting report. I believe you are on the right path.
  • BenK's avatar
    BenK
    Explorer
    Nov 09, 2021
    If I read your setup & changes...that much bigger ATF cooler is keeping your automatic cooler **AND** if your plumbed it back to OEM...that new ATF cooler is sending *COLDER* ATF into the main radiator.

    Meaning it was adding cooling capacity to the main radiator and maybe no more with the bypass. Depends on what that bypass is set for

    Ask what the 'after market' radiator is, as the OEM radiator is aluminum

    How many row?

    Staggered?

    Flattened?

    How many pass or sections?

    How many fins on the internal ATF radiator ?


    Finally :

    Check if the thermostat in good order ? It might be sticking

    How many times has the OATs coolant been flushed ? and assume with OATs coolant, not the good old American Green, right?

    Check your fan clutch, they do wear out. Just changed mine and wanted severe duty, but NAPA didn't have one in stock. So it now has a HD duty fan clutch (they both couple at about the same percentage water pump shaft RPMs...diff is in the bearings keeping it from becoming airborne). NEVER install a 'standard' duty fan clutch on that engine
  • tim1973's avatar
    tim1973
    Explorer
    Nov 09, 2021
    Thanks for the reply. The transmission thermostat is set for 180. The new radiator I bought from radiator express. It’s a single row, however thicker than stock. The sales rep explained these provide considerably more cooling surface/capacity than oe. Instead of plastic coolers, all aluminum. Looking back I wonder if I should’ve opted for two row? Anyway, it Only gets warm when on freeway at speed. Cools down to 190-200 when in traffic. No fan clutch, has giant variable speed electric fan OE. Which works. I am still using the dexcool…and it was flushed very well, guess new ac delco tstat could be hanging up, won’t rule it out of course…but doubtful. So, yeah, I was not sure whether or not to plausible.
  • BenK's avatar
    BenK
    Explorer
    Nov 10, 2021
    Interesting...what were the other options for that radiator ?

    Mine is a 1996 7.4L and it has OEM 3 row aluminum radiator. With a 7 fin ATF in tank radiator (cold tank). Albeit plastic tanks, but they aren't much involved in cooling.

    Maybe 'thicker' meant it has more rows, but just a guess, but since you say 'should've opted for 2 row'...says that single row is lower in cooling capacity

    Didn't know electric fans and must say not kept up with the newer models. Last time checked electric fan kits all said not for big block nor diesel. Maybe they have come up in fan electric motor HP these days.

    Oh well, you seem to be happy with the results and enjoy your ride !
  • tim1973's avatar
    tim1973
    Explorer
    Nov 10, 2021
    Hooked camper up this evening. Went for a 40 mile ride. 4 lane 65mph the whole way. Engine temp, rock solid at 190, transmission temp 190-194. I’m pleased so far. Thanks alot guys. BTW…the oe radiator is a single row, and the one I bought was also a single row, albeit the row looks wider…wider fins/probably tubing too. They did offer a two row, which the sales rep didn’t recommend. But looking back I might’ve felt more comfortable with the two row. Going to run this for now..and I think hopefully be ok??
  • jerem0621's avatar
    jerem0621
    Explorer II
    Nov 15, 2021
    Good post. I have a 2011 Tahoe without the factory external trans cooler. I added a 40K transmission cooler plumbed after the factory in radiator cooler. I’ve been thinking about adding a thermostat between the radiator cooler and the external trans cooler. I’ve ran it for 40k miles without the thermostat but my trans only gets to about 140° when not towing.

    My hottest temp while towing on a 95° day was 198° In the middle of the day in traffic. It stayed there for about 5 minutes and went back down to its normal towing temp around 180°.

    Love towing with my Tahoe.

    Thanks!

    Jeremiah
  • hornet28's avatar
    hornet28
    Explorer
    Nov 17, 2021
    Another radiator fact that many are unaware of is the difference the number of fins per inch can make. The more fins the more cooling surface. Years ago I had a BBC CC and hauled an 11ft camper pulling a 4 horse trailer. I needed a new radiator and after the install I couldn't even going up an overpass on the x-way caused the temp to go up. The radiator shop felt it was the truck and tested everything imaginable without finding anything wrong. Just as I was ready to swap radiators with a friend to try his the shop called and told me he'd found there was one with more fins, it amounted to over 3,000 more. He swapped it out at no charge and that did the trick. I hauled with that truck another 8 yrs without any problem. I changed radiators on my duallie last year and a shop tried selling me one that had less fins than the OE. He told me that was all that was available. I refused it and got on the internet and finally found a seller who was willing to count the fins instead of just telling me they sold factory replacements.
  • 1320Fastback's avatar
    1320Fastback
    Explorer
    Nov 17, 2021
    I believe all aftermarket cooler manufacturers recommend their coolers be put in before the factory radiator so it can warm the fluid back up if overcooled or then help cool it more if severely over heated.
  • Campfire_Time's avatar
    Campfire_Time
    Explorer
    Nov 17, 2021
    I'm wondering if you have an air flow issue. The factory cooler should work just fine. That trailer is well within the capability of the truck.

    I'm curious, is the grill shell the factory one, or is it an aftermarket replacement? Some aftermarket grills restrict air flow and cause transmission overheating. Or is there something else behind the grill?

    I had an aftermarket grill shell on my old '08 Sierra, it was on when I bought it. It always ran close to 200 towing, which didn't really bother me. Until towed on the bypass around Indy on a 98 degree day. It was running 215-230. I realised it was the grill, took it off for the rest of the trip and it never ran higher than 190, and that was in the mountains in TN. Most of the time it was at 170-180.
  • tim1973's avatar
    tim1973
    Explorer
    Nov 18, 2021
    Thanks for the replies guys. As far as the air flow, it’s got the factory grill guard. It only got warm..and it seems this is normal on gm type trucks…when at speed on the highway. Which led me to believe the cooling was inadequate. In fact both the transmission and the engine coolant were running too warm for my liking. I’m leaving Friday for a 130 mike trip. Am hoping it’s uneventful, and the upgraded cooling system works as it should.

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