Forum Discussion

mikgills's avatar
mikgills
Explorer
Feb 07, 2016

trans temperature downhill

I have a 95 Chevy Roadtrek 210 (G30 ext) 4L80 trans. HD cooling and factory aux trans cooler.
On long uphills engine temp and trans temp climb, as expected, but on the downhill engine temp goes down while the trans oil keeps going up (2nd gear). Pulling over and reving up rpms only helps until the thermostat fan disengages. After that i have no cool down and temp remains high. I have flushed the oil coolers (2) and changed trans oil every trip but same thing keeps happening. Did not know about this before adding trans oil temp gauge. trans has gone into limp mode a couple of times before adding gauge (reason for adding gauge), No service engine light. It appears the 2nd gear even on decent increase the oil temp rather than decreases.
Any body else notice this on 4L80 trans? Fan is working as it should. What can be done to prevent the increasing temp? Any experience with this tranny running hot? (95 does not have tow/haul mode). (115K miles)
  • Gene_Ginny's avatar
    Gene_Ginny
    Explorer
    Feb 09, 2016
    I noticed that with my 4Runner going up and down the hills in Maine. Seems if I keep my foot lightly on the gas after the top of the hill the temp comes down faster that just coasting. In my case I get concerned if my ScanGauge shows 210(f).
  • BarneyS's avatar
    BarneyS
    Explorer III
    Feb 08, 2016
    Might be that you have a clogged radiator (21 years old). Might be time to have it rodded out or maybe even replaced.
    Barney
  • Lynnmor's avatar
    Lynnmor
    Explorer
    Feb 08, 2016
    mileshuff wrote:
    My tranny temp always seem to drop when going down hill. Possibly because I use an exhaust brake?


    No, an exhaust brake will put more load on the transmission and less load on the service brakes.
  • sch911's avatar
    sch911
    Explorer
    Feb 08, 2016
    Turtle n Peeps wrote:
    How hot does it get?


    Yes what do you consider hot? We test these transmission's to very high temperatures during development. Max temps can go as high as 250F on Davis Dam testing...
  • mileshuff's avatar
    mileshuff
    Explorer
    Feb 08, 2016
    My tranny temp always seem to drop when going down hill. Possibly because I use an exhaust brake?
  • Trackrig's avatar
    Trackrig
    Explorer II
    Feb 08, 2016
    It does seem strange you're overheating that badly. For that size of MH, even though it's small, you might be about at the limits of the transmission.

    Where are the oil coolers mounted? If they're up in front of the radiator, I'd move them or install a couple more back in the frame rails. Install the types that have their own fans.

    HD oil cooler with fan

    Back in the long frame rails I'd also install at least one of these on each side.

    Oil heat sinks

    It sounds like the transmission needs all of the help it can get. I'd also change to synthetic oil for the extreme temps you're getting - if you haven't done so already.

    I'd also go to a larger oil pan such as the Mag-Hytec. They help cooling, but also the additional oil volume in the additional oil coolers and the oil pan will hold down the high temps longer.

    Mag-Hytec oil pans

    Bill
  • Lynnmor's avatar
    Lynnmor
    Explorer
    Feb 07, 2016
    Actually the transmission is working hard holding back. The internal friction and the torque converter losses are about the same in either mode. You can read about braking "horsepower" in diesel engine forums, and you would be surprised at how much power is going thru the transmission while holding back.

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