Keeping coolant and transmission temps under control when towing in the summer heat

[swathdiver]

But the fact that heat has been an issue for these trannys you don't think a cooler like a 40k which drops temps to 130ish is a benefit?

Not as much as we'd like to think. Mine has the stock cooling system and rarely sees 200 degrees in normal driving. If I want to check the transmission fluid, I have to drive it hard just to get the temp up above 160 for the "hot" check. Highway cruising it is in the 140s. If I were to tow more often, I would just change the fluid more often.

Back in April I hauled a 6K load for about 45 minutes through rush hour traffic and city streets. This included a fairly steep ascent to 65 feet from sea level to cross over the river and then down again after about a mile. Transmission saw a high of 183 near the end of the run.

The guys are coming back and reporting on the need to lower the TruCool down low as the heat it is shedding is heating up the radiator coolant.

 

[Fless]

Back in April I hauled a 6K load for about 45 minutes through rush hour traffic and city streets. This included a fairly steep ascent to 65 feet from sea level to cross over the river and then down again after about a mile. Transmission saw a high of 183 near the end of the run.

65 feet? 650 or 6500 ft?

 

[Geotrash]

But the fact that heat has been an issue for these trannys you don't think a cooler like a 40k which drops temps to 130ish is a benefit?

I don't. GM's own engineers have said that 150ºF is the minimum they want to see in continuous operation. And here is a quote from their orange manual:

+++++++++++
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.
++++++++++++

 

[swathdiver]

65 feet? 650 or 6500 ft?

Hey, I'm in Florida Fless, 65 feet is way up there! Gotta let them sailboats head out to sea! LOL

@Geotrash Dave, that fluid life versus temp chart is awesome, always wondered if that existed somewhere.

While we're on the subject of 6L80s... Here is a reprint from my thread in 2018:

With the weather warming up there's been talk of transmission temperatures and some fellas have been adding and or upgrading external coolers to keep the temperatures in line.

The 6L80s normal operating temperature is between 160 and 200 degrees. This corresponds with the HOT check on the dipstick when checking the fluid level. Cold check temperatures are between 80 and 90 degrees and also have a corresponding mark on the dipstick; mine anyway.

The temperature range for the Service Fast Learn Adapts procedure is 158-212 degrees.

If the transmission's temperature reaches 266 degrees for 5 seconds the "Transmission Hot Idle Engine" warning will display on the DIC.

Code P0218 (Transmission Fluid Overtemperature) will set if the fluid is greater than 270 degrees for one minute. On a side note, the shop manual says trailer towing should occur in D4 to ensure the cooling system functions normally.

The Flash Point for AC Delco's Dexron VI fluid is 401 degrees.

There is a transmission oil life monitor within the Transmission Control Module and is visible and able to be reset with the Tech2. I reckon that it is also based on engine revolutions and transmission temperature, similar to the Engine Oil Life System.

 

[Fless]

Hey, I'm in Florida Fless, 65 feet is way up there! Gotta let them sailboats head out to sea! LOL

Man, around here that's a speed bump.

 

[Sparksalot]

Hey, I'm in Florida Fless, 65 feet is way up there! Gotta let them sailboats head out to sea! LOL

@Geotrash Dave, that fluid life versus temp chart is awesome, always wondered if that existed somewhere.

While we're on the subject of 6L80s... Here is a reprint from my thread in 2018:

With the weather warming up there's been talk of transmission temperatures and some fellas have been adding and or upgrading external coolers to keep the temperatures in line.

The 6L80s normal operating temperature is between 160 and 200 degrees. This corresponds with the HOT check on the dipstick when checking the fluid level. Cold check temperatures are between 80 and 90 degrees and also have a corresponding mark on the dipstick; mine anyway.

The temperature range for the Service Fast Learn Adapts procedure is 158-212 degrees.

If the transmission's temperature reaches 266 degrees for 5 seconds the "Transmission Hot Idle Engine" warning will display on the DIC.

Code P0218 (Transmission Fluid Overtemperature) will set if the fluid is greater than 270 degrees for one minute. On a side note, the shop manual says trailer towing should occur in D4 to ensure the cooling system functions normally.

The Flash Point for AC Delco's Dexron VI fluid is 401 degrees.

There is a transmission oil life monitor within the Transmission Control Module and is visible and able to be reset with the Tech2. I reckon that it is also based on engine revolutions and transmission temperature, similar to the Engine Oil Life System.

Those values seem crazy high for old school knowledgeable folks.

I’m not saying they’re out there just eye popping.

 

[swathdiver]

Those values seem crazy high for old school knowledgeable folks.

I’m not saying they’re out there just eye popping.

I hear ya. I too grew up when 200R4s and 700R4s were space age technology and we were glad to be rid of our 200Cs and Turbo 350s!

 

[Geotrash]

Those values seem crazy high for old school knowledgeable folks.

I’m not saying they’re out there just eye popping.

Yup! Fluid chemistry and seal technology have come a long way.

 

[donjetman]

x2 what Geotrash said.

 

[Geotrash]

Just realized I forgot to post an update here. This Derale 13960 transmission cooler setup is still working perfectly for me 2 years later. Fingers crossed, the Cold Case radiator is also still holding up great.

But the most important update is that the excerpt from the Orange GM manual I posted above that states that an external transmission cooler should be plumbed in series *before* the radiator's oil-to-water cooler. This has been superseded by guidance in the 'green' manual that says to run the fluid through the radiator heat exchanger first. Don't know why they changed, but it also matches my learning, as documented in this thread.

Happy towing, folks!