SKU: 3942758100

Mishimoto 2017+ GMC 6.6L Duramax L5P Transmission Thermal Bypass Valve Kit

Sale price$133.16 Regular price$147.95
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  • USA
  • CAN

Ships within 48 hours · Estimated delivery Aug 21 - Aug 26

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Description

Mishimoto 2017+ GMC 6.6L Duramax L5P Transmission Thermal Bypass Valve KitThe Allison transmission is the backbone of your L5P Duramax. It's responsible for transmitting large quantities of torque from your V8 diesel powerplant. This torque generates a lot of heat, and if that heat isn't dissipated, it can destroy your transmission. The transmission cooler does a good job of keeping trans fluid temperatures in check, but only if the fluid can reach it. The stock cooling system of the Allison 1000 transmission utilizes an in

The Allison transmission is the backbone of your L5P Duramax. It's responsible for transmitting large quantities of torque from your V8 diesel powerplant. This torque generates a lot of heat, and if that heat isn't dissipated, it can destroy your transmission. The transmission cooler does a good job of keeping trans fluid temperatures in check, but only if the fluid can reach it. The stock cooling system of the Allison 1000 transmission utilizes an in-line thermal bypass valve that controls fluid flow to the transmission cooler. The purpose of this valve is to prevent transmission fluid from flowing to the cooler until it reaches operating temperature. The thermostat inside this valve is prone to failure, however, and when that happens, the fluid never flows to the cooler, and the transmission can overheat. That's why Mishimoto has developed a thermal bypass valve upgrade for your 2017+ Chevrolet/GMC 6.6L Duramax. Our CNC-machined aluminum thermal bypass valve not only looks better than the stock unit, but it performs better too. This Mishimoto thermal bypass valve kit includes a fully serviceable thermostat for fast warm-up in cold climates. This kit also includes a thermostat bypass that can be installed to provide constant cooling in warm climates or for use in extreme driving/towing conditions. The Mishimoto thermal bypass valve features strategically machined internal passages, providing improved flow over the stock valve for more effective cooling. In addition, cooling fins machined into the valve body add even more heat dissipation. This 2017+ Chevrolet/GMC 6.6L Duramax L5P Thermal Bypass Valve Kit is built to last a lifetime with a durable black anodized finish and our Mishimoto Lifetime Warranty.
Shipping Notes
  • Free Standard Shipping on $100+ Orders to the USA.
  • Except Preorder products are shipped in 48 hours.
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Exchange/Return Notes
  • We offer a 30-day return/exchange service after receiving.
  • Final sale items are not eligible for returns or exchanges.
  • To process your return/exchange, please contact us at [email protected]
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SKU: 3942758100

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4.0 ★★★★★
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gerald johnson
Battle Creek, US
★★★★★ 5
GDI ally.
Number of Items: 1
Seems to be effective at reducing oil consumption issue common in many GDI engines.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on May 2, 2026
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Verified Purchase
Lonnie S.
Massapequa, US
★★★★★ 5
I would highly recommend this product.
Number of Items: 1
I’m going to purchase this product again. I drive a lot and it’s perfect for me and yes, it does work in my opinion. I noticed a difference right away after the oil change. My vehicle was much smoother.
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Reviewed in the United States on May 15, 2026
G
Verified Purchase
Geoffrey Marsh
Louisville, US
★★★★★ 5
Great for Subaru oil consumption
Number of Items: 1, Number of Items: 1
Got this for my 2015 Subaru outback for its notorious oil consumption. It seems to be doing the trick causing less oil consumption after 1k miles noticable difference for sure.
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Reviewed in the United States on January 4, 2026
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Verified Purchase
GEORGE A SNARSKI
Omaha, US
★★★★★ 5
great for any engin
Size: 12 fl. oz. (Pack of 1)
Have been looking for this for a long time.i always used when i had a ,chevy 327,300.3speed.the engin always run great and when we changed the value cover gaskests the inside look like brand new,and clean.
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Reviewed in the United States on May 31, 2026
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Verified Purchase
Citasio
Cuba, US
★★★★★ 5
Great product
Size: 12 fl. oz. (Pack of 1)
Noticeable difference in the first 50 miles .
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Reviewed in the United States on March 30, 2026

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