Get Your Duramax Ready for Winter: Glow Plugs, Block Heaters, Thermostats and High Idle Kits

Here in the Midwest, the leaves are changing and deer season is open. That means cold and snow are only a month or two away. Without fail, the first real cold snap of every winter brings a wave of phone calls and emails about hard starts and weak cab heat, and the advice we give every one of those customers is the same: give your truck a good once-over before freezing temperatures hit.

A few hours in the garage this fall beats a no-start in a frozen parking lot in January. Below is the short list our technicians walk through on every Duramax heading into winter, along with the parts you need to fix what you find.

1. Glow Plugs: Your First Defense Against Hard Starts

A diesel engine has no spark plugs. It relies on the heat created by compression to ignite the fuel, and on a cold morning the cylinder walls and head soak that heat up fast. Glow plugs give the combustion chamber the extra heat it needs so combustion can happen when you turn the key. When one or more of them fail, you will usually notice longer cranking, a rough idle or misfire for the first few minutes, and white smoke on cold starts.

If your truck has codes for glow plug issues, now is the time to address them, before you really need them. You don't want to find out your glow plugs are bad when the weather turns on your snowmobile trip in the middle of nowhere. Glow plug circuit codes P0671 through P0678 point to a specific cylinder, which makes it easy to pinpoint the problem plug.

Genuine ACDelco Glow Plugs for Every Duramax

We stock genuine ACDelco glow plugs for the LB7, LLY, LBZ, LMM, LML, L5P and also the 2.8L LWN and 3.0L LM2 and LZ0 engines. For DIYers, we have also built complete kits for the 2001- 2016 6.6L engines designed to get the job done in your own garage, with the plugs and the tools packaged together.

Each Deluxe Glow Plug Replacement Kit includes eight ACDelco glow plugs, terminal nuts, anti-seize, wheel well liner clips and a clip removal tool, plus the same glow plug removal tools we use in our own shop: an air hammer, air nipple, air hammer tip and a removal socket machined to the correct depth. The LB7 kit also includes both glow plug rails for federal emissions trucks. You will need an air compressor capable of 4.5 CFM at 90 PSI to run the air hammer.

Already have plugs? The tools are also sold on their own: the Glow Plug Removal Tool Kit, the Removal Tool Adapter and Socket and the Duramax Glow Plug Reamer, which cleans carbon out of the bore so the new plug seats properly. You can browse everything in our Glow Plugs and Related category.

2. Block Heaters: Test Them Before You Need Them

The block heater warms the engine coolant, and with it the whole engine, while the truck is plugged in. A warm engine cranks easier, starts faster and puts heat into the cab sooner. Because it sits unused for most of the year, it is also one of the most overlooked parts on the truck, and people usually don't think about it until there is a problem.

The block heater and cord should be tested and inspected before winter to make sure everything is in proper working order. Check the full length of the cord for cracked or chafed insulation, a melted or burnt plug end, and bent or corroded prongs. Every winter we get a few trucks in with a damaged block heater cord, and a damaged cord can cause real issues once it's plugged in. If the cord looks good but the engine still isn't warming up, the heating element itself may have failed.

You can replace just the cord, or the element and the cord together:

3. Thermostats and Water Pump: Getting Heat Back in the Cab

If you notice that your Duramax is not getting up to operating temperature, and you are getting minimal heat in the cab as a result, it is worth checking the thermostats and the water pump.

Thermostats

The 2001 - 2016 Duramax uses two thermostats: a front thermostat that opens at 185°F and a rear thermostat that opens at 180°F. If one of them sticks open, coolant flows to the radiator before the engine is warm, and the truck struggles to reach temperature, especially at highway speed in the cold. Swapping the thermostats is a fairly easy job, and we sell them in kit form with both thermostats and the seals you need. Making sure the thermostats are working lets the truck get up to proper operating temperature and keeps the cab warm.

• Duramax Thermostat Kit, Front and Rear for 2001 - 2010 LB7, LLY, LBZ and LMM
• Engine Coolant Thermostat Kit for 2011 - 2016 LML
• Engine Coolant Thermostat Kit for 2017 - 2026 L5P
• Housings, gaskets and seals are in our Thermostats category

Water Pump

The Duramax water pump can be a difficult job, but if yours is leaking, now is a great time to address it. Watch for coolant drips or crusty residue at the front of the engine, a coolant level that keeps dropping, or a sweet coolant smell after a drive. A leaking water pump leads to a loss of coolant, and low coolant can make heating the cab a real challenge.

• Water Pump Kit with Cover and Seals for 2001 - 2005 LB7 and LLY
• Water Pump Kit with Cover and Seals for 2006 - 2016 LBZ, LMM and LML
• Water Pump Kit with Cover and Seals for 2017 - 2025 L5P
• See every option in our Water Pumps category

A healthy cooling system matters all year long. It's what keeps the heat blowing on your way out ice fishing in January, and it's the same system that keeps the truck cool in July when you're towing the camper.

4. High Idle Kits for LB7 and LLY Trucks

For our LB7 and LLY owners, a high idle kit is one of the easiest and least expensive ways to make winter more bearable, and in our opinion it's a must-have for getting the truck warmed up. The kit lets you use your factory cruise control buttons to bring the engine up to an elevated idle while the truck is in Park or Neutral. The engine warms up faster and so does the cab. Once you're driving, your cruise control works just like it always has.

Installation is simple and can be done in under an hour. And if you need to keep the truck running for an extended period, whether that's at a job site, at deer camp or out on the ice, the extra RPM helps with oil pressure and reduces the risk of injector issues that can come from long stretches at a low idle.

Good to know: the kits use the factory cruise control switch, so your truck needs cruise control. Trucks with the ZF6 manual transmission need an added switch, and the kit may not work if an aftermarket tune is installed. Installation instructions and a how-to video are on each product page.

Winter Prep Questions and Answers

Written by Joe Hilgendorf, Merchant Automotive Technician