8L90 Transmission Cooler 2018

Search for an 8L90 transmission cooler on a 2015-2018 Silverado 1500 or Sierra 1500 and this is often the part that actually solves the problem. To be plain about what you get: this is not a cooler core. It is a black anodized 6061-T6 billet aluminum bypass block, supplied with O-rings, that takes the place of the factory thermostatic bypass so the cooler already on your truck sees fluid all the time. It is listed for 5.3L and 6.2L trucks and SUVs with the 8L90, including 2015-2017 Tahoe, Suburban, Yukon, Yukon XL, Escalade and Escalade ESV.

What a bypass block changes in an 8L90 cooler circuit

From the factory, the 8L90 sends fluid past the cooler until a thermal element in the external bypass valve opens. GM bulletin 22-NA-182 puts that opening point at 194 F (90 C), compared with 158 F on the 6L80 and 6L90. Until then, the cooler does almost nothing. A billet block has no thermal element at all, so there is nothing to stick shut and fluid is routed through the cooler from the moment the engine starts. TransGo sells the same idea for 2015-on 8L90 units as a cooler flow bypass delete, and it lists all-time cooler flow and lower fluid temperature as the result.

Signs your 8L90 needs the bypass fixed

• Trans temp that runs up quickly with a trailer, a loaded bed or long grades, then drops slowly.
• Warm-engine shudder or harsh shifts, two of the complaints GM ties to overheating in 22-NA-182.
• Fluid that has darkened early or smells burnt.
• A straight, undamaged cooler line and clean cooler, yet the temperature problem stays.
• A replacement thermostatic valve already installed once and the overheating came back.

Check the cooler line first

A twisted rubber cooler line restricts flow and produces exactly the same complaint, and GM tells technicians to inspect and untwist it before touching the bypass. The full procedure, including the level reset afterward, is in our 8L90 cooler line guide. If the shudder is still there once temperatures are under control, the converter clutch and valve body are next; 8L90 valve body symptoms and testing explains how to separate those.

Fitment

Listed vehicles are the 2015-2018 Chevrolet Silverado 1500 and GMC Sierra 1500 with the 5.3L or 6.2L and 8L90, plus 2015-2017 Tahoe, Suburban, Yukon, Yukon XL, Escalade and Escalade ESV with the 8L90. It does not fit trucks with the 6L80. Because GM used different bypass valves and line sizes on the 8L90 over the years, compare your factory valve with the product photos, port for port, or send us your year and VIN before you order. Everything else we stock for this transmission is on the 8L90 shop page.

Install notes

• Let the truck cool, set a pan under the factory valve and expect some fluid loss from the cooler circuit.
• Remove the factory valve, fit fresh O-rings from the kit and mount the block in the same position with the stock line routing.
• Run the engine, check for leaks, then bring the fluid to the GM check temperature and set the level at the pan plug. The 8L90 has no dipstick from the factory; GM specifies DEXRON HP.
• Since you are draining fluid anyway, it is a good time to deal with a warm shudder using the 8L90 shudder fix kit, or to add a locking dipstick and fill tube so future checks are easy.

The trade-off is honest and simple: with no thermostat, warm-up is slower in winter. For a truck that tows or works, steady cooler flow is usually worth it.

Is this an actual transmission cooler?

No. It is a billet bypass block that replaces the factory thermostatic bypass so your existing cooler receives fluid all the time. If your cooler core is leaking or damaged, you need a cooler, not this block.

Does it fit a 2018 Tahoe or Yukon?

The SUV fitment listed is 2015-2017. For 2018 SUVs send us your VIN so we can check the valve and line style before you order.

Will it fit the 6L80?

This block is listed only for 8L90-equipped trucks and SUVs. A 6L80 truck needs a different part.

Why does my 8L90 run hot even with a clean cooler?

GM says the factory 8L90 bypass does not open until 194 F, and a sticking element or a twisted cooler line can keep fluid out of the cooler longer. Check the line first, then the bypass.

What fluid and how much after install?

Use DEXRON HP and top up only to the level-plug procedure at temperature. Only the fluid lost from the cooler circuit needs replacing, not a full refill.

• 8L90 Cooler Line Replacement: Diagnosis, Procedure and the Fluid Reset
• 8L90 Valve Body Symptoms and Testing
• 8L90 Common Problems and Fixes
• 8L90 Pump Failure Symptoms and Replacement