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Transmission temperature

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by TDCulbyy763, Feb 24, 2014.

  1. CKNSLS

    CKNSLS Member 2 Years 100 Posts

    Jcat-

    Please show a link where GM says over 200 degrees is harmful. This seems to be an Internet myth.
    Last edited: Feb 25, 2014
  2. RayVoy

    RayVoy Active Member 2 Years 1000 Posts

    Good possibility that my chart is 20 years old, I just found it on the net. But, even if it is 20 years old, Dexron III is 20 years old, so, let's assume it applies to III.

    Dexron, III, and VI are both synthetic ATF (all synthetic ATF starts with a base petroleum stock). The major differences are the viscosity and the additives. The viscosity for VI is lower than the viscosity for III; normally, this is not a good thing. However, the additives make VI better in all measurements. BTW, the reason the spec calls for a lower viscosity is due to the close tolerances in GM's 6 speed transmissions.

    This may be so, I think we need to see the source data.


    Just to toss my two cents into this discussion, let's not look at the max temp the fluid can handle (because we don't know that spec), let's look at the complete powertrain cooling system.

    The radiator cools the engine, by forcing air over fins, lowering the temp of the water based coolant.
    This same radiator cools the transmission fluid.
    On some vehicles, the same radiator cools the engine oil.

    We all know the normal engine temp (pressurized cooling system) is between 200 and 210 degrees F

    The radiator successfully keeps the engine coolant at the correct temp.

    This same radiator would not be as successful if the transmission fluid was so hot that it raised the internal temp of the radiator.

    It makes sense to me, that the cooling system would be designed to maintain a temperature of around 200 degrees F) for the 3 main engine, transmission fluids.

    My 2 cents

    And, I just thought of something else. Generally, transmissions take longer to get up to normal temp that the engine, during this time, it is possible that the transmission fluid will absorb some heat from the engine via the radiator. A reverse of the "normal" ATF cooling procedure.
  3. CKNSLS

    CKNSLS Member 2 Years 100 Posts

    Your chart has been floating around the net for more than twenty years probably closer to 30 years. BTW-It was wrong back then too. I will show you my source data when anyone who has replied on this thread can show me source data where GM SAYS over 200 degrees is harmful. (Guess what-I already know the answer and I know you can go to the end of the Internet and it doesn't exist).

    This 200 and your transmission is overheating is nonsense.

    You don't have to educate me on oils-I have spent PLENTY OF TIME over at bobistheoilguy.com
  4. Conlan Rose

    Conlan Rose Active Member 2 Years 1000 Posts

    Guys, even tho the information you are posting may be relevant and useful, you are detracting from the original question of the OP. His question about his tranny temp is while driving unloaded under normal conditions, NOT while towing or beating on the truck. Is 200 bad? I have no clue I'm not a transmission expert, but in cooler weather under normal conditions the tranny shouldn't run very hot. Also if the vehicle has over 100,000 miles it is due for a tranny fluid change and filter change, that's what the normal/max change interval is for a GM tranny to my knowledge.

    I know all of you could argue about this for days but please keep on track with helping out the OP not arguing about what trannys can handle under max conditions.

    BTW to be honest if the OP's truck has 100,000 miles and the fluids stayed at 175-200 the whole time owning the truck and it needs new fluid that makes the chart partially right.
  5. j cat

    j cat Rockstar 3 Years 1000 Posts

  6. Phil_R

    Phil_R New Member

    As a result of this thread, I decided to monitor the transmission temp of my new truck during a chore trip. Subject: 2014 Silverado 1500 Regular Cab Work Truck, 4.3L V6 and 6-speed auto-transmission. Start miles 103 on odometer, end of trip 171 miles on odometer, 68 miles total during test. Average air-temperature 78f degrees, (North Florida) longest distance and maximum speed 60 MPH, 10 miles (each way, 20 total) on rural Hwy 90. Load weight of 500 pounds, including driver weight.

    Using DIC to monitor transmission temps, 20 miles travel for transmission to attain full temp. (187f ~ 189f degrees... engine temp, 200f) Maximum transmission temp of 192f degrees, in-town portion of trip, and final 1/4 mile of rough lime-rock grade to home. With 171 miles total on truck, I will occasionally monitor transmission temp for changes during break-in… I’m going to trust GM on this one, and just drive the truck.

    DIC fuel mileage average at end of trip, 23.3 MPG... driving conditions light and easy.
  7. CKNSLS

    CKNSLS Member 2 Years 100 Posts

  8. j cat

    j cat Rockstar 3 Years 1000 Posts

    that forum posting was his statement not the GM engineers statement...meaning he may have miss understood this "GM ENGINEERS" report.

    seems strange that if the engineers comments are truely made by him that the GM tranny temp guage only goes up to 260 deg f..

    ALL on that forum never reported those 270 plus temps !

    - - - Updated - - -

    looks good to me. no problems with those temps.
  9. Phil_R

    Phil_R New Member

    Todays temperature check... air temp 55f degrees, transmission fluid 187f degrees after 20 miles. Checked DIC temperatures against ScanGauge II, never more than 01f degree difference between gauges. I'm satisfied with the accuracy of DIC. 25f degree drop in air temp had little effect on transmission temperature.
  10. CKNSLS

    CKNSLS Member 2 Years 100 Posts




    JCAT
    Please reread.

    General Motors’ in-house towing team expert provided RV Clinic with this statement: The maximum allowable automatic transmission fluid temperature is dictated by the transmission oil itself. The oil begins to degrade significantly above 270 degrees Fahrenheit, so we design vehicles so that in all but the most extreme conditions, the fluid temperature in the transmission sump stays below 270 degrees F.

    This statement is very direct-if you wish to discount it-that's your opinion.
    Last edited: Feb 26, 2014

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