6L90 Transmission Cooler, new and ready to install. Fits the 6L90. Ships fast from the USA.
This is not a radiator-style transmission cooler. It is a new cooler bypass valve upgrade kit built to the STL010 pattern for the GM 6L90 and 6L80, the small cartridge that decides whether fluid goes to your cooler at all. If a 2014-or-newer Silverado or Sierra HD, Express or Savana van, Tahoe, Yukon or Suburban shows high transmission temperatures while towing, sets an overtemp warning, or starts to shudder and shift harshly with darkened fluid, a thermal bypass valve that opens late or not at all is a common reason.
From 2014 on, GM routed the 6L cooler lines through a thermal bypass valve, or TBV, in a block on the side of the transmission. Cold fluid is sent straight back into the unit so it warms up quickly; as it heats, the valve opens and sends fluid out to the cooler. GM's own bulletin 21-NA-199 states the original valve is not fully open until 194 F, and the revised valve, stamped 70, is fully open at 158 F. On a heavy truck working a grade or pulling a trailer, that late opening lets heat build before the cooler gets any flow. This kit replaces the factory valve internals with a sleeve, piston, spring, check ball and new O-rings so fluid reaches the cooler full time, with a pressure bypass built in. It installs in the existing block and keeps the factory lines.
GM TechLink gives a simple test. Drive until the scan tool shows about 190 F fluid, check that the pan surface temperature matches with an infrared thermometer, then measure both cooler lines about six inches from the valve. In normal operation the return line is cooler than the line going out. If both lines are cooler than the pan and the valve body is hotter, the TBV is not opening. Also check for a twisted cooler line, which GM documented as a separate cause of overheating and shift complaints on low-mileage units. Our 6L90 common problems guide and Silverado 2500 6L90 guide cover the overheating failures in more detail.
The kit is listed for 2014-and-up GM 6L80 and 6L90 units with the side-mounted cooler line block, and for 2016-and-up 8L80/8L90 and 10L90 units that use the same valve style. GM's bulletin covers 6L trucks and vans through 2021, including the 2020-2021 Silverado and Sierra 2500HD/3500HD. Units built before 2014 have no TBV and do not need this kit. It is an aftermarket kit, not a GM part. Look at your cooler line block before ordering, or send us your year and VIN and we will confirm. See the rest of the hardware on the 6L90 parts page.
| Fits | 6L90 |
| Part type | Transmission Cooler |
| Condition | New |
| Brand | GM |
| Reference | STL010 |
| Ships | From the USA |
| Warranty | 1-year |
No. It is a thermal bypass valve upgrade kit, STL010 type, that installs in the 6L80/6L90 cooler line block so fluid reaches your existing cooler full time.
GM added it to the 6L80 and 6L90 in 2014. If your cooler lines enter a block with a valve on the side of the transmission, it does. Earlier units do not need this kit.
Neither. It is an aftermarket replacement kit built to the STL010 pattern, with a sleeve, piston, spring, check ball and O-rings.
The kit is rated for close to 20 percent lower average operating temperature. Actual results depend on load, cooler condition and airflow.
Dexron VI. Only the fluid lost during the swap needs replacing. Set the level hot with the engine running.
