When it comes to cold-starting a diesel truck’s Cummins, Power Stroke, or Duramax engine, two technologies dominate the conversation: glow plugs and grid heaters. Both serve the same fundamental purpose of making cold starts easier by preheating the air in the combustion chamber, but they go about it in different ways. Whether you’re just into YouTube cold-start videos or truly want to understand what your truck is doing on those frosty mornings, here’s the breakdown between glow plugs and grid heaters.

What Are Glow Plugs?

Glow plugs are small, electric heating elements that sit inside each cylinder’s pre-chamber or directly in the cylinder. When you turn the key or push the start button, the glow plugs heat up rapidly, bringing the combustion chamber to a temperature where diesel fuel can ignite more easily.

How Do Glow Plugs Work?

Glow plugs, reaching temperatures over 1,000 degrees Fahrenheit in seconds, act like mini heating rods. Powered by the battery and controlled by a relay, they glow red-hot to ensure that the compressed air/fuel mixture ignites properly in cold conditions, even if the engine block is ice cold.

What Diesel Trucks Have Glow Plugs?

Glow plugs are now the standard for today’s diesel trucks. As of model-year 2025, the Big 3’s (Ford, GM, Ram) diesel truck engines all use glow plugs: Power Stroke, Duramax, and Cummins. Yes—Cummins dropped the grid heater in favor of glow plugs for model-year 2025 Ram Heavy Duty trucks. This marks one of the big changes for the latest Ram trucks.

What Is A Grid Heater?

A grid heater, on the other hand, is a heating element installed in the air intake system, usually between the air filter and intake manifold. Instead of heating each cylinder individually, it warms up the incoming air before it even reaches the combustion chamber.

How Does A Grid Heater Work?

When activated, the grid heater heats the air passing into the intake manifold, raising its temperature before it gets compressed in the cylinders. This helps cold air combust diesel fuel more efficiently.

Glow Plugs: Pros and Cons

Advantages:

• Faster warm-up: Glow plugs heat up in 2–5 seconds, meaning you get quicker cold starts.
• Targeted heating: Each cylinder gets its own glow plug, which is more efficient in colder temps.
• Lower overall power draw: Each plug draws relatively little current, spread across the system.

Disadvantages:

• More parts to fail: With 6 or 8 glow plugs, you have more potential failure points.
• Harder to service: Especially on V8 engines (like Power Stroke and Duramax), access can be a pain.

Grid Heater: Pros and Cons

Advantages:

• One part, easy access: No need to pull valve covers or manifolds—grid heaters are easy to replace.
• Reliable design: Fewer moving parts and no small wires to break.
• Works well for inline engines: Especially Cummins’ inline-six, where preheated air is enough.

Disadvantages:

• Slower warm-up: Grid heaters take longer to heat intake air versus glow plugs heating the chamber.
• Heavy electrical draw: Can demand 100–200 amps during operation, which taxes the battery and alternator.
• Catastrophic failure: For Cummins-powered Ram trucks, a fatal design flaw allows a nut to come loose and fall into the intake tract, thereby killing whichever cylinder it enters.