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Mishimoto

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

4.7 store rating · 575 reviews
SKU: MISMMTC-L5P-TBVFF

Fits 2017–2019 Chevrolet Silverado 2500 HD / 3500 HD, 2017–2019 GMC Sierra 2500 HD / 3500 HD · 6.6L Duramax

All 16 applications
$105.99
Only 4 left. Ships in 1–2 business days.
15750 Entries150X
This purchase enters you to win FSD26, a 2024 F-350 Limited and $20,000 cash. See the truck · No purchase necessary
  • Authorized dealerGenuine Mishimoto parts, sourced direct
  • 30-day returnsSee the return policy
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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.

  • Durable CNC-machined billet-aluminum construction
  • Eliminates failure-prone bypass valve
  • Installs in less than 1 hour

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Good to know

Questions, answered straight.

If it is not here, call or text the counter. Real people, real answers.

Fitment

  • Will this fit my truck?

    The Fits section at the top of the page lists the manufacturer's applications for this exact part. If your year, make and model is not there, or you are not sure, text us a photo of what you are replacing with your year and engine and we will confirm it before you order.

  • What if I order the wrong part?

    Call or text us before it ships and we will swap it. After delivery you have 30 days to return it in new, uninstalled condition. The return policy has the restocking details.

Shipping

  • When will it ship?

    In-stock parts usually ship within 1 to 2 business days from warehouses across the USA. The stock line under the options tells you the status of the part you are looking at. Large items ship LTL freight and we call to schedule delivery.

  • Why did I only get part of my order?

    We ship from multiple warehouses, so an order with several items can arrive in more than one box. Tracking for each shipment is emailed as it goes out. Full details in the shipping policy.

Returns and warranty

  • What is the return policy?

    30 days from delivery, in new and uninstalled condition, with a restocking fee. Everything is spelled out in the Returns & Refund Policy.

  • How do warranty claims work?

    We are an authorized dealer, so the manufacturer's warranty applies to every part we sell. Call or text us with your order number and we handle the claim with the brand for you.

Paying

  • Can I pay over time?

    Yes. Shop Pay installments are offered at checkout on qualifying orders, and the monthly estimate shows right under the price.

  • What is a core deposit?

    Some remanufactured parts, like injectors and turbos, carry a refundable core deposit. It is shown on the product page when it applies and refunded when your old part comes back to us.

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Why buy here

A diesel shop that sells parts, not a website that sells boxes.

Every part on this site is one our own techs can stand behind.

  • We run what we sell

    A working diesel repair and fabrication shop in Nazareth, PA. These are the parts our techs install every week.

  • Real techs on the phone

    Call or text 908-223-9744 and you get a diesel tech, not a script.

  • Authorized dealer

    Genuine parts straight from the manufacturer, with the factory warranty behind them.

  • Fast from stock

    Most in-stock parts ship in 1 to 2 business days from warehouses across the USA.

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  • 7+ Years in business
  • 6+ Shop technicians
  • 30,000+ In-stock SKUs
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Full Send Diesel, Nazareth, PA

A team of diesel people, not a call center.

Full Send Diesel is a shop full of techs, builders and parts people in Nazareth, Pennsylvania. When you call or text, you reach someone who works on these trucks and knows the parts.

Not sure what you need? Send a photo of what you are replacing with your year and engine. We will point you to the right part, confirm it is in stock, and get it moving.

Call 908-223-9744 Text us Email

Mon–Fri, 8am–4pm ET. After hours, text or email and we answer first thing in the morning.

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