2015 and 2016 Duramax Thermostat Replacement

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Few names in the automotive industry carry the reputation of the “Duramax” diesel engine. If you’re a Chevy or GMC truck enthusiast, then you’ve undoubtedly encountered this engine. The Duramax engine isn’t just another diesel powerplant; it’s a symbol representing relentless power.

Duramax engines have evolved to meet stricter emissions standards without sacrificing their impressive power. Of course, this power generates a lot of heat, so eventually, you’ll have to replace the thermostat. We’ll take a close look at the process involved in 2015 and 2016 Duramax thermostat replacement.

What Causes Thermostat Failure in the Duramax Engine?

A thermostat is a relatively simple mechanical component, but it can experience wear and tear over time. Understanding the common causes of thermostat failure will help you identify when it’s time to change out this crucial component. It also helps you identify situations when other engine problems might be causing damage to the thermostat.


Not even your Duramax powered truck can outrun time. The constant exposure to temperature fluctuations causes the valve to open and close repeatedly. This repeated motion causes the thermostat to become less responsive when regulating engine temperature.

Stuck Closed

One of the most common problems with thermostats is when they get stuck in the closed position. This means that the thermostat valve doesn’t let water pass once the engine warms up. Common causes of the valve being stuck closed is the accumulation of debris.

Stuck Open

On the other end of the spectrum, thermostats also get stuck open. This means that the valve remains open, even while the engine is warming. While it might not lead to immediate overheating, it results in poor fuel efficiency and increased engine wear because the engine never reaches its optimal operating temperature.


Exposure to coolant causes corrosion in the thermostat housing. Corrosion affects the thermostat’s ability to open and close properly. The most common cause of corrosion is neglecting to change the coolant at recommended intervals.

Regular maintenance, including coolant changes and inspections, help prevent thermostat problems and ensure that your engine operates at the right temperature. If you suspect thermostat issues, it’s essential to address them promptly to prevent potential engine damage.  If you are unsure, one way to nail down the actual issues going on in your engine is by using an OBD2 scanner.


…And, our recommendation of the best aftermarket replacement thermostat for the Duramax engine is:

As you can see, this is a relatively inexpensive part.  The Mitzone replacement thermostat kit is compatible with the 6.6L v8 Duramax engine and will work on many Chevy and GMC models ranging from years 2001 – 2019.  They feature high grade stainless steel and copper construction.

How to Replace a 2015 or 2016 Duramax Thermostat

2015 or 2016 Duramax thermostat replacement is a manageable DIY task if you follow these steps carefully, and it doesn’t cost a lot. However, if you’re uncomfortable performing any step in this process, it’s always a good idea to consult a professional mechanic to ensure the job is done correctly.

Here’s a step-by-step DIY how- to guide for the thermostat replacement process:

Step 1: Gather Your Tools

Here’s a list of what you’ll need:

  • New thermostat and gasket
  • Coolant
  • Socket set with various-sized sockets
  • Screwdrivers (Phillips and flathead)
  • Pliers
  • Drain pan
  • Funnel
  • Hose clamp pliers (optional)
  • Safety goggles and gloves

Step 2: Locate the Thermostat Housing

The thermostat housing is usually located near the front of the engine. It’s connected to the upper radiator hose. On the 2015 and 2016 Duramax models, it’s usually on the driver’s side. You may need to remove the air intake duct or other components to access it.

Step 3: Drain the Coolant

Place a drain pan underneath the vehicle. Then find the radiator drain valve, usually located on the lower driver’s side of the radiator. Open the valve and allow the coolant to drain into the pan. Be sure to dispose of the used coolant properly.

Step 4: Remove the Thermostat Housing

Carefully remove the bolts holding the thermostat housing in place. Keep these bolts in a safe place, as you’ll need them for reinstallation. Once the housing is loose, use pliers to disconnect the upper radiator hose from the housing. Some hose clamp pliers can be handy for this step.

Step 5: Replace the Thermostat

Inside the housing, you’ll find the old thermostat. Carefully remove it. Pay close attention to its orientation. Replace it with the new thermostat, ensuring it’s installed in the same position as the old one. Make sure to use the new gasket as well.

Step 6: Reassemble and Refill

Reattach the upper radiator hose to the thermostat housing and secure it with the hose clamp. Then, reattach the thermostat housing using the bolts you removed earlier. Tighten the bolts securely, but don’t overtighten since that damages the housing. This is a tricky step so be extra careful.

Step 7: Refill Coolant

Refill the radiator with fresh coolant. Be sure to consult your owner’s manual for the correct type and mixture of coolant for your Duramax engine. Fill it until it’s at the proper level.

Step 8: Bleed the System

Start the engine and let it run for a few minutes with the radiator cap off. This removes air bubbles that form in the coolant. As the engine warms up, you’ll see the coolant level drop. Continue adding coolant until it stabilizes at the correct level.

Step 9: Check for Leaks

After turning off the engine, check for any coolant leaks around the thermostat housing and radiator connections. If you spot any leaks, address them before driving the vehicle.

Final Thoughts

2015 and 2016 thermostat replacement isn’t too difficult of a task. The tricky step is ensuring that you don’t overtighten the new thermostat. Also, keep in mind that proper maintenance gives your new thermostat a longer lifespan. If you find yourself replacing your thermostat too often, then there might be a problem with another part of the engine. In that scenario, you’ll need to take your truck into a licensed mechanic to track down the problem.

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