High trans temps with new TC

YYC-SIERRA · December 26, 2023

2018 Sierra 5.3 with 6L80E

Recently installed a Circle D converter with 2600-2800 stall speed, as part of a big upgrade.

Had the truck tuned for the new camshaft, converter, etc etc.

Everything works great, good power, smooth driving etc.

However, when going up the ski hill at 45ish MPH, the truck stays around 2500-2600 RPM. The trans temperature climbs pretty quickly to above 210, as high as 225 at one point.

I noticed the automatic shutters in the grill stay CLOSED so minimal airflow is reaching the radiator. The coolant temp also reads slightly higher than normal during this time.

I assume since the RPM of 2500ish is close to the TC stall speed, it's probably generating alot of heat?

2 questions......why would my shutters be closed when both coolant and trans temps are sky high? The outside temp is low 30s, high 20s. Might I need a new temperature control switch for the shutters?

Also, does it sound like the tune is causing my RPM to stick in the mid 2ks for extra power, at the expense of extra heat. Would installing a Tru-Cool 40k be a good idea? Or should I get it re-tuned.

Other than this issue with going up hill, it's drives perfect.

rav3 · December 26, 2023

If you have not done the "pill flip" or transmission thermostat bypass upgrade, your transmission is set to run high to start with. Not sure what your issue is but I personally would do tge simple "pill flip" to have transmission to run cooler. Search YouTube on this.

YYC-SIERRA · December 26, 2023

I deleted the thermostat by way of pill flip a couple years ago.

Standard temp is 135F on the highway and 180 in the city. It never gets hot EXCEPT in this very specific situation of extended driving around 2500rpm uphill.

I'm really curious why my shutters won't open when the fluids are both very hot.

rlcole321 · December 27, 2023

that's the problem with higher stall converters, slippage does generate heat, I did the DOD delete on my 18 'Rado, BTR stage II cam and Long tubes, and kept the same stock converter and with my HPTuner, made the adjustments for the better idle control with no issues. I'd would just open the shutters, unplug and delete the code for the shutter controls and see if that helps. If you didn't know, your trans cooler is in the top of the AC condenser. Did you install a colder coolant thermostat?

YYC-SIERRA · December 28, 2023

21 hours ago, rlcole321 said:

that's the problem with higher stall converters, slippage does generate heat, I did the DOD delete on my 18 'Rado, BTR stage II cam and Long tubes, and kept the same stock converter and with my HPTuner, made the adjustments for the better idle control with no issues. I'd would just open the shutters, unplug and delete the code for the shutter controls and see if that helps. If you didn't know, your trans cooler is in the top of the AC condenser. Did you install a colder coolant thermostat?

Thanks, I'm pretty sure it's the result of the higher stall converter and the way it was tuned to generate more torque in the lower gears.

I bought a Tru Cool 40k and will see if that helps.

Stock coolant thermostat, pill flipped the trans thermostat. Cheers