Fixes the GM 6L80/6L90 cold-fill flaw so the cooler charges right away, drops running temps by up to 20 percent, and lets you check fluid level without a warm-up cycle.
If your 2014 or newer Silverado, Sierra, Tahoe, Yukon, Suburban, Escalade, Express or Savana with the 6L80 or 6L90 runs hot when towing, shows a high transmission temperature on the dash, or you are tired of warming the truck up just to check the fluid, the thermal bypass valve in the cooler lines is a big part of the story. The Superior STL010 Sure Cool kit changes how that valve circuit behaves so fluid goes to the cooler from the start instead of waiting on a thermostat.
Starting in 2014, GM put a thermal bypass valve, or TBV, in the 6L80 and 6L90 cooler circuit. When the fluid is cold the valve sends it straight back to the transmission and skips the cooler, which helps warm-up and fuel economy. GM TechLink states the original valve does not fully open until 194 degrees F. Under load that means the transmission runs warm before it ever gets cooler help, and a valve that sticks or opens late leaves the fluid running hot all the time. GM later released an updated valve, stamped 70, that is fully open at 158 degrees F. The Sure Cool kit goes further: it installs in the existing cooler line block on the transmission and gives full-time cooler flow with a built-in safety bypass, so the cooler fills immediately. The maker rates it for up to 20 percent lower average operating temperature.
GM's overheating diagnosis is simple with an infrared thermometer. Warm the fluid to about 190 degrees F, then compare the pan surface to the scan tool temperature. Measure the bypass valve itself and the cooler lines about six inches from the valve. On a healthy circuit the return line is cooler than the line going out. If both lines read lower than the pan while the valve reads hotter, the valve is not opening. Also check that air can get across the cooler. Heat is behind several of the failures in our 6L80 common problems and fixes guide, and the 6L80 Escalade common problems guide covers how it plays out on the heavier SUVs.
Listed for GM 6L80, 6L90 and 8L90 transmissions that use the cooler line thermal bypass valve, which generally means 2014-and-later trucks, SUVs and vans. GM's own TechLink lists the 6L80 and 6L90 overheating concern on 2014-2020 Tahoe, Suburban and Yukon and 2014-2021 Silverado, Sierra, Express and Savana. Earlier 2006-2013 6L80 units without a TBV block on the cooler lines have nothing for this kit to replace. Look for the valve block where the cooler lines meet the transmission before you order, or send us your year and VIN. Other parts for these units are on our 6L80 parts page.
Work on a cool transmission. Disconnect the cooler lines at the valve block, keep track of the small O-rings, and install the Sure Cool components in the block following the kit instructions, then reconnect the lines and check for leaks with the engine running. Top up with Dexron VI. On most of these trucks there is no dipstick, so the level is set at the check plug with the engine running at operating temperature; an ATF filler adapter makes adding fluid much easier. If the fluid is already dark, this is the right time for a pan, filter and fluid service with a 6L80 pan kit with drain plug. After install, watch the temperature on your next tow to confirm the drop.
| Fits | GM 6L80, 6L90, 8L90 |
| Function | Immediate cooler fill with built-in safety bypass |
| Benefit | Up to 20 percent lower average operating temperature |
| Also | Accurate fluid level check without a warm-up cycle |
| Result | Reduced overheat risk under load, longer ATF life |
| Ships from | USA |
Only if the truck has a thermal bypass valve block where the cooler lines meet the transmission. GM added that valve starting with 2014 models, so most 2006-2013 trucks have nothing for this kit to replace. Check for the block or send us your year and VIN.
GM's updated valve is still a thermostat; it is fully open at 158 degrees F instead of the original 194 degrees F. The Sure Cool kit sends fluid to the cooler right away with a built-in safety bypass, so the cooler is working from the first mile.
The maker rates it for up to 20 percent lower average operating temperature. Results depend on the cooler, load and weather, so log your temperature on a familiar tow before and after.
Check the level at the check plug with the engine running and the fluid at normal operating temperature, as GM specifies. Because the cooler fills right away, the reading is more consistent than with a closed factory valve.
Dexron VI. Top up after installing the kit, since some fluid is lost when the cooler lines come off.
