Glow Plugs vs Intake, Block, and Coolant Heaters for Cold Weather Diesel Generators

This article explains what glow plugs are, how they differ from intake, block, and coolant heaters, and when each option makes sense for diesel generators operating in cold weather.

What Are Glow Plugs?

Glow plugs are electrical heating elements used in many diesel engines to assist with starting in colder temperatures. Diesel engines ignite fuel through compression heat, not spark. When ambient temperatures drop, compression alone may not generate enough heat for clean ignition. Glow plugs add localized heat right where combustion begins.

What Glow Plugs Do in a Generator

• Improve cold-start reliability
• Reduce cranking time
• Promote cleaner initial combustion
• Reduce startup stress on engine components

Glow plugs are powered by the generator’s onboard battery and operate only during startup. They help the engine fire when it’s cold, but they do not keep the engine warm while it is sitting idle.

Intake Heaters, Block Heaters, and Coolant Heaters

1) Intake Air Heaters

• Warm air before it enters the engine
• Improve ignition quality during cold starts

Intake heaters assist only during startup. They do not keep the engine block or coolant warm during extended cold weather.

2) Block Heaters

• Warm the engine block itself
• Reduce cold-start wear after long idle periods

Block heaters are designed to keep the engine warm while the generator is off. They only operate when another power source is available and are commonly controlled by a manual switch or breaker.

3) Coolant (Jacket Water) Heaters

• Maintain warm engine coolant
• Keep the engine closer to operating temperature

Coolant heaters serve the same purpose as block heaters but focus on warming the coolant instead of the block. They are optional and typically used where fast, reliable cold starts are critical.

Where Block and Coolant Heaters Get Their Power

All ASE diesel generators start using an onboard battery. That battery powers the starter, controller, and glow plugs.

Block and coolant heaters work differently. They are intended to keep the engine warm before an outage occurs. Because the generator is not running at that time, these heaters only operate when another power source is available.

Typical Standby (Utility Power Available)

In most standby installations, block and coolant heaters are powered by normal building utility power. They keep the engine warm while the generator is waiting. When utility power fails, the heaters shut off and the generator starts using its battery.

Grid-Tied Solar

In grid-tied solar systems, utility power still exists. In these setups, heaters are typically powered by utility power, not the solar system, and operation is the same as a standard standby installation.

Off-Grid or Solar-Only Systems

In fully off-grid systems, block and coolant heaters only operate if they are intentionally connected to the solar battery and inverter system. Many off-grid sites choose not to power these heaters to avoid draining batteries.

Even without engine heaters, the generator will still start normally — it simply starts from a colder condition.

Can Glow Plugs Replace Other Cold-Weather Heaters?

In most cases, no. Glow plugs assist ignition during startup but do not keep the engine warm. Intake, block, and coolant heaters each address different cold-weather challenges.

Can Glow Plugs Alone Save Money?

Glow plugs alone may be sufficient in mild or moderate climates where extreme cold soak is uncommon. In colder climates or mission-critical standby applications, additional engine heating can improve readiness.

ASE Generators Equipped With Glow Plugs