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- USA
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Ships within 48 hours · Estimated delivery Jul 7 - Jul 12
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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 full-flow thermal bypass valve upgrade for your 2017-2019 Chevrolet/GMC 6.6L Duramax. Our CNC-machined aluminum full-flow thermal bypass valve not only looks better than the stock unit, but it performs better too. This Mishimoto thermal bypass valve eliminates the internal thermostat, providing full fluid flow to the transmission cooler in all running conditions. This setup is ideal for owners in warm climates, those performing heavy towing, and trucks needing the best possible cooling efficiency for their transmission. 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 adds even more heat dissipation. This 2017-2019 Chevrolet/GMC 6.6L Duramax L5P Full-Flow Thermal Bypass Valve Kit is built to last a lifetime with a durable black anodized finish and our Mishimoto Lifetime Warranty.This Part Fits:
| Year | Make | Model | Submodel |
|---|---|---|---|
| 2017-2019 | Chevrolet | Silverado 2500 HD | High Country |
| 2017-2019 | Chevrolet | Silverado 2500 HD | LT |
| 2017-2019 | Chevrolet | Silverado 2500 HD | LTZ |
| 2017-2019 | Chevrolet | Silverado 2500 HD | WT |
| 2017-2019 | Chevrolet | Silverado 3500 HD | High Country |
| 2017-2019 | Chevrolet | Silverado 3500 HD | LT |
| 2017-2019 | Chevrolet | Silverado 3500 HD | LTZ |
| 2017-2019 | Chevrolet | Silverado 3500 HD | WT |
| 2017-2019 | GMC | Sierra 2500 HD | Base |
| 2017-2019 | GMC | Sierra 2500 HD | Denali |
| 2017-2019 | GMC | Sierra 2500 HD | SLE |
| 2017-2019 | GMC | Sierra 2500 HD | SLT |
| 2017-2019 | GMC | Sierra 3500 HD | Base |
| 2017-2019 | GMC | Sierra 3500 HD | Denali |
| 2017-2019 | GMC | Sierra 3500 HD | SLE |
| 2017-2019 | GMC | Sierra 3500 HD | SLT |
Shipping Notes
- Free Standard Shipping on $100+ Orders to the USA.
- Except Preorder products are shipped in 48 hours.
- Delivery to the USA:
- Standard Shipping : 3-10 business days
- If time is of the essence, please consider selecting expedited delivery for faster service.
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]
- Please click here for more details>>> Return & Exchange Policy
4.8 ★★★★★
Based on 1772 reviews
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Product Reviews
★★★★★ 5
Customer Favorite for Comfort & Everyday Wear
Size: 4X-Large, Color: Safety Green, Size: 4X-Large, Color: Safety Green
I absolutely love the Fruit of the Loom Men’s Eversoft Fleece Crewneck Sweatshirts! These have quickly become a staple in our store because they deliver exactly what our customers want — comfort, durability, and a clean, classic look.
The fleece is incredibly soft on the inside without being too heavy, which makes it perfect for everyday wear, layering, or working outdoors. One thing I really appreciate is how breathable and moisture-wicking the fabric is. Even after hours of wear, it still feels comfortable and not overly hot, which is important for active days or changing temperatures.
The fit is true to size and the extended sizes up to 4X are a huge plus. It’s not always easy to find quality sweatshirts in larger sizes that still look good and hold their shape, but these definitely do. They wash well, keep their softness, and maintain their color without shrinking or fading.
If you’re looking for a dependable, comfortable sweatshirt that looks great and feels even better, this is a solid choice. Whether for casual wear, work, or relaxing, you really can’t go wrong with this one.
Highly recommend!
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Reviewed in the United States on February 18, 2026
★★★★★ 4
Nice material, quality, comfortable
Size: X-Large, Color: Safety Green
Nice quality, soft. He likes it! It does run a bit big in the shoulder, but overall he likes the fit. Would purchase this one again.
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Reviewed in the United States on March 4, 2026
★★★★★ 5
Super Comfortable Crewneck
Size: Medium, Color: Grey Heather
This has become the sweatshirt that somehow disappears from the closet first.
The fleece is soft without feeling overly heavy, and the fabric has a bit of breathability so it stays comfortable for everyday wear. It works well as a simple layer for cooler days or lounging.
The fit is relaxed and the crewneck style is easy to throw on over a T shirt.
One of those straightforward sweatshirts that quietly ends up getting worn a lot.
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Reviewed in the United States on March 5, 2026
★★★★★ 5
Cozy and soft
Size: 4X-Large, Color: Red
This brand of sweatshirt is true to color and size. I find it is cozy and well made. It has some stretch and give but only enough to be comfortable, not so much that it looks weird.
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Reviewed in the United States on May 18, 2026
★★★★★ 5
Nice & comfortable
Size: XX-Large, Color: Grey Heather, Size: XX-Large, Color: Grey Heather
This is a nice & comfortable sweat shirt. I wear a 2X and this fits me comfortably. The stitching is right on as there are no loose threads anywhere on the shirt. This shirt is medium thickness & has a little bit of stretch to it, which is all one needs. From underwear to sweatshirts FOTL has does a great job once again. For the price paid you are getting a great value for your money.
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Reviewed in the United States on March 23, 2026