Transmission- how hot is too hot?

[Juanitos2008]

just do the tranny thermostat bypass mod or remove the tranny thermostat all together

[HondaHawkGT]

While this was the accepted standard at one point, I'm not sure that holds with today's fluids and trantsmissions?

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There are different versions of Dexron VI. Some are conventional/syn blends and others are full synthetic. I would assume GM put the lower grade blend in these trucks.

[HondaHawkGT]

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/22474061/gotomsg/22475137.cfm#22475137

 

Here is a quote from the Orange ($8.95) GM manual:

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"OIL TEMPERATURE MEASURED AT CONVERTER OUTLET TO COOLER.

 

300F is the maximum temperature. (Workhorse says 350F). This is the normal place to install a temperature gauge or signal. The temperature in this location will vary significantly with each vehicle start-up or hill. If the temperature reaches 300F (350F), reduce throttle. To lower the transmission temperature with the transmission in NEUTRAL, run the engine at 1,200 RPM for 2-3 minutes to cool the oil. Do not allow the converter outlet temperature to exceed 300F (350F).

Keep a close check to prevent the engine cooling system from overheating.

 

300F would be typical of rocking the vehicle in mud, snow, or sand, or a transmission in stall (full throttle, no vehicle movement). When the transmission is in stall, the transmission will develop heat at a rate of one degree per second of stall.

 

OIL TEMPERATURES MEASURED IN THE SUMP

 

150F -- Minimum operating temperature for continuous operation. It is possible in low ambient temperature to overcool the transmission with oil to air-type coolers; it is hard to overcool if used in conjunction with oil to water coolers installed in most standard automotive radiators.

 

190F-200F -- Maximum oil level checking temperature. Beyond this, readings are not reliable because of expansion.

 

285F -- Maximum sump/oil pan temperatures for short duration such as a long hill climb.

 

300F -- Metal parts inside the transmission begin to warp and distort in varying degrees, seals melt rapidly, and transmission fluid life is extremely short due to oxidation and distress.

 

AUTOMATIC TRANSMISSION FLUID OXIDATION Automatic transmission fluid

can provide up to 100,000 miles of service before oxidation occurs under normal operating temperatures of about 170F. Above normal operating temperatures, the oxidation rate doubles (useful life of the fluid is cut in half) with each 20 degree increase in temperature. The approximate life expectancy at various temperatures is a follows:

Degrees F Miles

175 100,000

195 50,000

212 25,000

235 12,000

255 6,000

275 3,000

295 1,500

315 750

335 325

375 80

390 40

415 Less than 30 minutes

 

After-market temp gauge should be installed in the lower (hot) line entering the lower fitting of the radiator.

 

After-market external oil to air cooler should be installed in series. The hot oil line should go first through the aftermarket cooler then into the radiator to maintain proper minimum temp of the trans in low ambient temps.

 

End of GM copy from orange manual.

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[truckguy82]

That is not an accurate chart.

 

That predates dextron, let alone dextron iv

[HondaHawkGT]

Hey fellas just wondering how hot is too hot for these transmissions. I have a 2014 reg cab 4.3 work truck that spends 99% of its time off the pavement. I was on my way to work this morning in the woods and I was in 4x4 pushing snow and spinning and the temperature was up to 110 degrees Celsius (230 F) just wondering how hot is too hot and if there was a warning? Thanks

If you're concerned about the fluid oxidizing, you can follow the severe duty service interval in your owners manual. I believe GM recommends changing the fluid at 45k miles in severe duty situations. Don't let people nag you about changing it early. You're the one making the truck payments.

[sdeeter19555]

That is not an accurate chart.

 

That predates dextron, let alone dextron iv

That chart contradicts what's in the quoted part of that manual!

 

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[redwngr]

There are different versions of Dexron IV. Some are conventional/syn blends and others are full synthetic. I would assume GM put the lower grade blend in these trucks.

These trucks don't use dexIV.

 

They're at Dex VI for the 6 speed.

 

The 8 speed uses Dex HP

[HondaHawkGT]

These trucks don't use dexIV.

 

They're at Dex VI for the 6 speed.

 

The 8 speed uses Dex HP

Oops I did't notice I flip-flopped letters. Thanks for catching that.