8L90 Transmission Cooler, new and ready to install. Fits the 8L90. Ships fast from the USA.
Most people who search for an 8L90 transmission cooler are chasing heat: a Silverado, Sierra, Tahoe, Yukon or Escalade that climbs on the temperature gauge when towing, throws a hot-transmission warning in summer traffic, or starts to shudder once it is fully warm. This listing is not a new cooler core. It is a small cartridge kit built to the STL010 pattern that goes inside the factory thermal bypass valve housing, so the cooler you already have actually gets fluid. For $58.99 it is the cheapest fix to try once the cooler lines and fluid check out.
The 8L90 does not send fluid straight to the cooler. Fluid leaving the case first passes an external thermal bypass valve, which routes it back to the transmission until it is hot, then opens the path to the cooler in the radiator. GM's bulletin 22-NA-182 gives the 8L90 opening point as 194 F (90 C), the highest of any GM rear-drive automatic in that bulletin; the 6-speeds are listed at 158 F and the gas 10-speeds at 143 F. That late opening means an 8L90 already runs warm before it is cooled at all. If the thermostatic element wears or sticks, the valve opens late or not at all and the fluid keeps climbing.
This kit replaces the internals of that valve with a sleeve, piston, spring, steel check ball, one small O-ring and two large O-rings. The idea is full-time flow to the cooler instead of a temperature-switched gate, while the housing and lines stay factory.
Rule out the no-cost causes first. Bulletin 22-NA-182 says a twisted rubber cooler line on low-mileage trucks can cause overheating, shudder, surge and flare, and on some units sets DTC P27EC; our 8L90 cooler line replacement guide shows what to look for. Shudder alone is usually the fluid: GM's 18-NA-355 fix is a full exchange to Mobil 1 Synthetic LV ATF HP, covered in 8L90 common problems and fixes. If the lines are straight and the fluid is fresh, warm the truck past 200 F and feel or use an infrared thermometer on the line leaving the valve toward the radiator. A cold outbound line with a hot pan means the valve is not sending fluid to the cooler.
The listing describes this kit for 2016-and-newer GM 8L90 applications, and the same STL010 pattern for 2014-up 6L80/6L90 and the 10L90. Note that 2015 8L90 trucks are not named in the listing, and GM moved the 10-speed bypass valve into the valve body on most gas trucks, so many 10L90s have no external housing for this kit to go into. Before ordering, remove your valve cap and compare the cartridge with the kit photos, or send us your year and VIN and we will check it. The kit is aftermarket, not a GM-boxed part. More parts for this unit are on the 8L90 and 8L45 parts page, and if you would rather replace the whole valve, the 8L90 thermal bypass valve with 3/8 inch line is a complete assembly.
| Fits | 8L90 |
| Part type | Transmission Cooler |
| Condition | New |
| Brand | GM |
| Reference | STL010 |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. It is a rebuild cartridge for the factory thermal bypass valve: sleeve, piston, spring, check ball and three O-rings. It makes the cooler you already have do its job.
The listing names 2016-and-newer 8L90s. 2015 is not listed, so compare your valve cartridge with the photos or send us your year and VIN before ordering.
GM bulletin 22-NA-182 lists 194 F (90 C) for the 8L90, with the valve mounted outside the transmission.
DEXRON HP only. GM's shudder bulletin uses Mobil 1 Synthetic LV ATF HP, which meets that specification. You only need to replace what drained out.
Yes. Look for a twisted rubber cooler line, which GM says can cause overheat and DTC P27EC, and confirm the fluid has been exchanged for shudder complaints.
