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PAThwacker's avatar
PAThwacker
Explorer
Jul 21, 2014

HOT 300 degree 4l80E

Mid season update on our Subs 4l80E. I have taking the truck to a shop at the beginning of the season for hot towing concerns and given a clean bill of health. I have figured out why and which RPMs to be at to effectively control the TQ. This past weekend we camped in the Catskills, NY and had no spikes climbing north. The ride home was A-0k at 190 to 220F.

enter NY thruway south with sluggish traffic 45 to 52mph, tow haul on, and i watched the gauge spike to 300 and then the hot trans light came on. I stopped the truck for 40 minutes and continued home for 2 more hours at 190F.

i called a new shop and they feel the factory cooler is blocked. I can not believe that the 4th gear sluggish event is enough to roast the fluid. Is it something else?

We are barely towing a full height trailer 7ft 6"w by 9ft 6" tall w/ac.

Will adding an auxilliary cooler, and cap off factory cooler be merely a bandaid or final fix to the old school 4l80E?

24 Replies

  • Are you towing in 4th gear or 3rd? I ask because your post makes it sound like you are towing in 4th. That's bad at any speed with the older 4 speeds. With the 4 speed, TH mode only changes the shift pattern from a dead stop. It doesn't control the shifting between 4th and 3rd or prevent OD from being used. OD kicks in at 40 so if you are in 4th and going between the speeds you were it doesn't surprise me that it heated up. At those low speeds it doesn't take much of a speed change to force it to downshift into 3rd. Constant shifts between 3rd and 4th and back again will generate a lot of heat.

    Are you using Dex VI when you do a fluid change? It's recommended for your truck even though it had Dex III in from the factory. Dex VI came out in 2006. Its a synthetic blend and runs far cooler than Dex III did.

    A trans can take short bursts above 220 without permanent damage. But 300? I dunno. That's a scary high temp.

    EDIT: If you add an auxillary cooler, don't bypass the factory cooler, put it inline.
  • It might be you had enough load on the tranny in 4th gear so the torque converter would not lock up causing additional heat.
  • The two times I had heating problems it turned out to be the fan clutch. Eventhough it seemed fine, once I replaced the clutch the heating problem went away.

    I also added Royal Purple "Wetter Water". It helped keep the temp from rising on 6 to 10 % grades when towing.