6L, 8L & 10L Transmission Cooler Adapter with Thermostat, 140ºF

In stock

6L, 8L & 10L Transmission Cooler Adapter with Thermostat, 140ºF

Improved Racing created the first bolt-on transmission fluid adapter with a thermostat for GM's 6L, 8L, and 10L automatic transmissions.

The adapter's built-in thermostat automatically bypasses the transmission cooler until the fluid reaches operating temperature. The thermostat reduces rough shifts caused by overcooled transmission fluid, reduces wear, and improves efficiency and horsepower. The transmission can now reach operating temps quickly while retaining the cooling capacity needed for high load activities such as towing or racing. It's the best of both worlds!

The adapter features SAE female -6AN O-ring boss ports that accept adapter fittings for 5/16", 3/8", 1/2" hose barbs or male AN fittings. This allows you to run common rubber transmission cooler lines or braided AN lines. Hard tube adapters may also be used to connect the factory lines directly to the adapter (may require minor bending or adjustment of factory lines).

Important Application Notes:

  • The adapter can only be used in conjunction with external transmission fluid coolers.
  • The adapter does not directly connect to the factory hard lines. Aftermarket lines or hard tube adapter fittings must be used.
  • The adapter will only help resolve rough shifting issues if they are caused by overcooling of the transmission, usually due to the addition of a larger aftermarket transmission cooler. Note that 8L45 and 8L90 transmissions rough shifting issues can often be resolved through GM TSB 18-NA-355 and by simply flushing the transmission fluid.

Features and Benefits

  • Bolt-on fitment for 6L, 8L, and 10L series General Motors automatic transmissions (adapters are required for connecting to factory lines).
  • Built-in thermostat prevents temperatures from dropping below optimal levels, reducing wear, improving efficiency and horsepower, and helping to eliminate rough shifting.
  • Rebuildable: Rebuild kits available, or send it back to us for a rebuild under warranty.
  • SAE -6AN female O-ring boss ports for connection flexibility; choose any line size and type you want.
  • 6061-T6 billet aluminum construction with black MIL-A-8625 Type II anodized finish.
  • Uses the factory GM transmission cooler adapter gasket.
  • Lifetime Warranty.
  • Made in the USA.

Optional hose barb and male AN adapter fittings available

Temperature Rating Specifications

Note: The 140ºF temperature rating is recommended for most applications.

Part Number Typ. Stabilization Temp Activation Temp Full Flow Temp
TGM-100-T1 145ºF (63ºC) 140ºF (60ºC) 163ºF (73ºC)
TGM-100-T2 165ºF (74ºC) 160ºF (71ºC) 181ºF (83ºC)


  • 1x TGM-100 transmission cooler adapter block with built-in thermostat
  • 1x Transmission cooler adapter gasket, GM Part # 23135703
  • 1x Zinc-plated steel mounting screws
  • Installation instructions


  • Fits most General Motors 6L, 8L, and 10L series automatic transmissions, including:
    • All 45, 50, 60, 70, 80, 90 variants, and aftermarket performance versions
    • Fits both E and non-E transmission variants
  • Applications include:
    • 6L45
    • 6L50
    • 6L80 / 6L80-E
    • 6L90 / 6L90-E
    • 8L45 / 8L45-E
    • 8L90 / 8L90-E
    • 10L80 / 10L80-E
    • 10L90 / 10L90-E
  • Note: Has not been verified to fit Allison 10L1000 transmissions (RPO code MGM & MGU)


Part #
Improved Racing
Part Weight
15.6 oz (443 g)
Primary Material
6061-T6 aluminum
Type II Anodized
Minimum Operating Temperature
-40°F (-40°C)
Maximum Operating Temperature
302°F (150°C)
Inlet Port Size
-6AN O-Ring Boss Female
Outlet Port Size
-6AN O-Ring Boss Female
Maximum Operating Pressure
300 psi (20.68 bar)
Max Recommended Flow Rate
Up to 5 GPM (19 LPM)
Fluid Compatibility
Gear oil
Transmission fluid
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