Do Cummins Engines Have Glow Plugs?

Glow plugs are the heating aids found in diesel engines. Since Cummins engines are in a league of their own, do their 5.9L and 6.7L engines have glow plugs? We've popped the hood, pointed our flashlight, and did the research for you.

Cummins engines do not have glow plugs. Instead of glow plugs, Cummins engines are equipped with a single heater grid as their heat aid. These grids are more reliable and work by heating all the heat coming into the air intake. Both the 5.9L and 6.7L Cummins engines come with a grid heat system.

Your diesel engine will be manufactured with some sort of heating device to help you avoid slow starts with cold engines. Heat grids are close to indestructible and can be changed at home if needed. We'll be discussing the grid system, block heaters, and more in this article!

The Cummins Heat Grid

In place of individual glow plugs per cylinder, there is one heat grid found in the intake manifold of the engine. The air passing through gets heated and will continue heating until the temperature gauge is at the correct programmed heat. While glow plugs will last up to 100k miles, your heat grid should last the lifetime of the car. 

A heat aid is necessary for diesel engines to prevent difficult start-ups due to colder weather and after long sitting periods. Even though the 5.9L is a fixed geometric turbo and the 6.7L is a variable turbo, both of the cylinder blocks take away heat from the combustion chamber. 

How long should you let a Cummins warm-up?

On the Cummins forum for 5.9L engine owners, they'll usually idle their engine for 2-5 minutes before driving. As for the 6.7L engines, the average idle time is 30 seconds to one minute. It seems to be a general consensus, however, that even after idling, you should still start your drive off easy before overloading the truck with power.

In colder weather, dropping to 32-15 degrees Fahrenheit, you should let your engine idle for at least 10 minutes. Idling it longer in colder temperatures will help reliquify the fuel which can turn to a gel consistency. You can also plug your block heater in for less idle time, but not in replacement.

How long can you leave a block heater plugged into a Cummins?

The great thing about block heaters is that you can leave them plugged in for hours or days. Keep in mind the type of engine and voltage you have because you will be shocked when your power bill comes up. A block heater warms up multiple fluids in your vehicles such as antifreeze, oil, and parts of the internal engine.

If you live in a very cold environment where the ambient temperature could get close to the negatives, leaving your vehicle plugged in overnight will help you have an easier start in the morning. However, you should still idle for another 5 minutes to ensure that heat is flowing for proper operation. 

On one Cummins forum, a user makes a great suggestion for what he does with his truck to save on electricity. This individual added a 110-volt thermostat to only turn on when the surrounding temperature got to 38 degrees Fahrenheit. Using a timed system helps keep power being used in check.

Tip: Be careful when running the car with the block heater on because you can overheat the engine.

What does a glow plug do in a diesel engine?

Glow plugs, like heat grids, add heat into the combustion chamber that may not make it from the cylinder block. The incoming air and fuel will heat quicker and result in more efficient fuel combustion. Pre-chamber engines have one plug per cylinder in the pre-chamber. Direct injection engines have one plug per cylinder but in the combustion chamber.

Diesel engines require more heat to get the engine started and therefore have glow plugs instead of spark plugs, which are found on gasoline cars. You'll be able to notice when your spark plugs go bad in cold weather before warm temperatures since they need to work harder. In 38 degrees or less temperature, bad plugs make the vehicle harder to start, give you a loss of acceleration, and overall lower power. If you have bad plugs in warm climates, you may not even notice.

Glow plugs come in two different versions: an in-cylinder and an in-manifold. The in-cylinder glow plugs will have a plug in every cylinder for direct injection. The second variety, an in-manifold, only has one plug for all the cylinders. Glow plugs are made up of a heating coil in a metal tube that is filled with electrically charged ceramic powder.

A bonus of good glow plugs: They help reduce the exhaust fumes emitted by the vehicle. 

Can a diesel start without glow plugs?

As seen with Cummins engines, glow plugs are not a standard feature of all diesel engines. No matter what though, some sort of heating mechanism will be needed, such as a heat grid. Plugs and grids don't have to work as hard with warm ambient temperatures but come in handy if you travel to somewhere cold. 

Are cold starts bad for diesel?

According to the Argonne Nation Laboratory, newer diesel engines can often cold start with no issues. The one exception is cold starts in colder climates. If diesel fuel becomes too cold, often at temperatures of 32 degrees and colder, it becomes thick and turns into a gel-like consistency. When it gets to this stage, there isn't enough vapor available for the combustion chamber to heat and start the engine. 

Some diesel drivers have run into the problem of not heating their vehicles enough and experience some form of engine failure. When this happens, you'll need to pull over and allow your engine to idle until the gauges are at normal operation levels. Too many cold starts will overwork the battery and chambers, leading to more wear and tear and maintenance. 

Can you use WD-40 to start a diesel engine?

As stated on the WD-40 website, their multi-purpose spray can be used to displace moisture. This means diesel owners can use it in a pinch if they don't have any starting fluid on hand. By adding WD-40 into the air intake system, the vapor will catch and help start the engine. 

In the past, ether was often used as a starting fluid. This method has become less and less popular due to the stripping damage it causes. The volatile nature of ether washes oil off the cylinder walls which will, in turn, reduce the amount of lubrication present. Since the wear and tear can also affect the compression, your diesel engine could become addicted to ether starts.

In Closing

Cummins engines have a heat grid in place of glow plugs in their 5.9L and 6.7L models. This heat aid allows heat to reach the combustion chamber and start the engine more quickly, especially in colder climates. Keeping your vehicle on a block heater and allowing it to idle before driving will help loosen the engine's liquids and give you a better overall performance.

Before you go, be sure to check out these other posts that may be of interest to you:

Do Cummins Have Blow-Off Valves?

5 Of The Best Fuel Injector Cleaners For Diesel Engines