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Thread: Towing in Overdrive

  1. #1
    Join Date
    Apr 2011
    Location
    Middletown Indiana
    Posts
    4

    Default Towing in Overdrive

    My '94 Sierra longbed has "don't use overdrive while towing a trailer" stamped right inside the drivers door. I'm a lawncare guy, and tow no more than a 3500lb. load. I don't mind driving in town short distances without overdrive. However; I have a 35 mile commute twice daily on a pretty flat road with only two stops. Can I leave it in overdrive on the commute??? Or am I just asking for trouble. Also: how high do you guys rev your 6.5s? I'm new to diesel (except for my John Deere 2440) so I find your opinions very valuable. Thanks

  2. #2
    Join Date
    Sep 2007
    Posts
    329

    Default

    I often tow a similar load - enclosed trailer with about 3500 lbs. I have also wondered about whether overdrive would be OK for the interstate and straight stretches of highway.
    1997 Silverado 1500 6.5. with 185,000 miles. New fuel injection pump at 132,000 mi. FSD Heat-Sync in bumper hole, marine fuel injectors, air induction kit all from Walt at 148,000 mi. Replaced OEM Fuel Filter Assy, wastegate solenoid valve, OPS and relay at 155,000 mi. Harmonic Balancer replaced. Red dot and White dot EGR replaced. New starter, Instant Heat glow plugs, and glow plug relay/controller at 180,000. Replaced hydroboost and master cylinder in 2016.

  3. #3
    Join Date
    Feb 2007
    Location
    Baja California Sur Mexico
    Posts
    2,804

    Default

    There should be an explanation on the label, but of course we are all stupid, so only need to be told "don't do it". In overdrive, there is no engine braking, so on the down hill, the brakes can overheat and cause loss of brakes. The engine has a rev limiter set at 3,400 rpm, but at 3,000 it is better to select a higher gear.
    Last edited by grancito; 01-21-2012 at 11:47 PM.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  4. #4
    Join Date
    Feb 2007
    Location
    Lincoln, NE USA
    Posts
    712

    Default

    The single biggest problem with towing in OD is putting too much torque load on the transmission by pulling long grades/steep short grades with much more than 4,000 lbs behind you. Heat is the main problem followed by clutch slippage in the torque converter and/or OD clutches which creates more heat and burns up fluid and clutches/steels. If your RPMS drop much below 2200 RPM or your tranny temp climbs past 200* (assuming you have a temp gauge on your tranny) drop it into D and take the strain off your tranny.

    That being said, with my '94 C2500 C&C with its steel utility box grossing 9K, a 3.42 rear and pulling a 20' steel dovetail with a Dodge Grand Caravan on it I was able to pull on the Interstate between Lincoln and Omaha which has some good rolling hills and two mile-long healthy grades on either side of the Platte River at 75 mph and dropped into D just to maintain RPMs climbing out of the Platte Valley. Of course the age/condition of your tranny also dictates as well as if you have an external cooler or not.

    For light towing such as a mower trailer, I wouldn't sweat it as long as you're not leaving it in OD at say 50mph while climbing - watch your RPMs and engine/trans temps.

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