Forum Discussion

wayfun's avatar
wayfun
Explorer
Oct 14, 2014

Holding in lower gear vs letting tow-haul mode shift

I tow with a 6 speed, 6.2L Tahoe. I usually tow around 55 to 60 mph. With the transmission in tow mode it is locked out of 6th gear and it generally stays in 4th and 5th gears on the highway. At 58 mph I'm at 2500 rpm in 4th and 2100 in 5th. However at a slight grade in 5th it shifts to 4th. If I hold it in 4th the truck just pulls. With the cruise set at 58 I can come to a significant grade and the truck just pulls on without shifting. My question is which mode would be easier on the transmission and torque converter? Intuitively I feel less shifting would be better but I've been told that allowing it to shift would make the transmission run cooler. What's the consensus here?

Dennis
Tow Vehicles
  • wayfun's avatar
    wayfun
    Explorer
    Oct 14, 2014
    kwlincoln wrote:
    important question... How heavy is your trailer?


    Loaded its 7800 lbs.
  • ktosv's avatar
    ktosv
    Explorer
    Oct 14, 2014
    wayfun wrote:
    Intuitively I feel less shifting would be better but I've been told that allowing it to shift would make the transmission run cooler.


    Actually, unless the torque converter immediately locks up, frequent shifting will result in more heat.

    If it is hunting for a gear and shifting on every grade and won't stay in any one gear for more than a couple of miles I would lock it in 4th.
  • kwlincoln's avatar
    kwlincoln
    Explorer
    Oct 14, 2014
    So you're definitely at full capacity of your truck. If it were a lightweight trailer, I'd say turn the tow haul off when not pushing the engine. I would only turn it on when pulling my pop-up on hilly roads or driving in stop/go traffic.

    Personally, I would recommend for you to keep the tow/haul on unless the road and wind conditions are favorable on flat land. You can sometimes turn it off to get that last gear for improved fuel economy in those favorable conditions. Otherwise, leave it on.

    Now I drive an F350 diesel, tow heavy and I always leave it on. But it also will shift into all 6 gears and by leaving it on, I take advantage of the improved engine braking.
  • time2roll's avatar
    time2roll
    Nomad
    Oct 14, 2014
    I would pull the lever to hold 4th if the transmission was inclined to shift or hunt during the climb. I would let the initial downshift (5->4) happen automatic. You can run 2500 rpm all day without issue so holding for an extended climb is not an issue. Once back on the flats let the transmission do what it likes.
  • Buck50HD's avatar
    Buck50HD
    Explorer
    Oct 14, 2014
    An unlocked torque converter is generally what makes heat, not high RPM. Most of the new vehicles will keep the converter locked in T/H mode if you are at highway speed. If they need more power, they just downshift instead of unlocking the converter. No slip = no heat.

    Also, the converter is usually unlocked at slower speeds, less than about 40MPH so that's also when heat can build quickly. Combine that with low airflow and that's when you can fry a trans.

    I usually run 5th with my 6.2 SD if it's nearly flat. Otherwise, if there is a series of slight grades that's causing it to shift repeatedly, I'll limit it to 4th. If it's really irregular terrain, I'll just run manual mode.
  • Greentreena's avatar
    Greentreena
    Explorer
    Oct 14, 2014
    The only time I lock mine in a gear it when it start hunting for the gear. It's always towing up a steep hill loaded so I lock it in 4th and let off the throttle. A bit.
  • brulaz's avatar
    brulaz
    Explorer
    Oct 14, 2014
    Buck50HD wrote:

    ...
    Also, the converter is usually unlocked at slower speeds, less than about 40MPH so that's also when heat can build quickly. Combine that with low airflow and that's when you can fry a trans.
    ...


    Even in Tow/Haul mode?

    When loaded I always use tow/haul unless it's hunting, primarily to keep the converter locked.
  • Dick_B's avatar
    Dick_B
    Explorer
    Oct 14, 2014
    I have a similar TV and use the `manual' mode much of the time even with Tow Haul mode to minimize shifting. IMHO the jury is still out on how long the transmissions will hold out with these little 6 L engines in tow vehicles.
  • wayfun's avatar
    wayfun
    Explorer
    Oct 14, 2014
    In 4th gear the truck doesn't struggle at all on significant hills. When holding it in 4th the tow/haul mode is still engaged. Would the torque converter be locked at those times?

    Dennis

About Travel Trailer Group

44,029 PostsLatest Activity: Jan 20, 2025