How to Test and Replace a Polaris Diesel Glow Plug

Unlike gas engines that rely on a spark, your Polaris Ranger Diesel depends on compression and heat to fire up. In cold weather, the Diesel Glow Plug is the unsung hero that pre-heats the combustion chamber. When these fail, your machine becomes an expensive paperweight the moment the temperature drops. Understanding how to diagnose a dead plug versus a relay issue can save you hours of cranking and unnecessary wear on your starter.

Symptoms of a Bad Glow Plug

If your diesel UTV is acting up, look for these specific "cold start" red flags:

• Hard Starting: The engine cranks for a long time before finally sputtering to life.
• Excessive White Smoke: Unburnt fuel exiting the exhaust after a cold start indicates the cylinders weren't hot enough.
• Rough Idle after Start: The engine misses or "lopes" for the first minute until cylinder heat builds up naturally.
• Dashboard Warning Light: The glow plug indicator light stays on too long or flashes.

Tools Needed for the Job

• Digital Multimeter
• Deep-well socket set (usually 10mm or 12mm depending on engine model)
• Ratchet and extension
• Torque wrench (inch-pounds)
• Compressed air or shop vac

Troubleshooting Table: Diagnosis at a Glance

How to Test and Replace a Diesel Glow Plug

1. Testing Resistance (The Continuity Test)

Set your multimeter to Ohms (Ω). Remove the electrical lead/bus bar from the top of the Diesel Glow Plug. Place the red probe on the terminal of the plug and the black probe on a clean ground on the engine block. A healthy plug should show very low resistance (usually under 2 ohms). If you see "OL" (Open Loop), the heating element is snapped inside.

2. Clear the Area

Before removing a plug, use compressed air to blow out the "well" around the plug. Diesel engines live in the mud; if any grit falls into the cylinder while the plug is out, it will score your cylinder walls instantly.

3. Removal and Installation

Carefully unthread the faulty plug. These can be brittle, so apply steady, even pressure. Thread the new plug in by hand first to avoid cross-threading the head. Use a torque wrench to tighten to factory specs—usually very light, around 10–12 foot-pounds (check your specific manual).

Common Mistakes to Avoid

• Testing with a Test Light: A test light only tells you if power is reaching the plug, not if the plug is actually generating heat. Use a multimeter.
• Overtightening: The tips of these plugs are thin metal. If you over-torque them, they can snap off inside the head, requiring a massive teardown to extract.
• Ignoring the Bus Bar: Corrosion on the metal strap connecting the plugs can prevent even a brand-new Diesel Glow Plug from getting enough juice.

When to Replace vs. Repair

A glow plug cannot be repaired. If the element is burnt or the resistance is out of spec, it must be replaced. If you find one bad plug, we strongly recommend replacing the entire set. If one has reached its end-of-life, the others are usually right behind it, and doing the job once is better than tearing the machine apart three separate times.

Related Parts You May Need

• Glow Plug Relay: If none of your plugs are getting power.
• Replacement Bus Bar: If yours is bent or heavily corroded.
• Diesel Fuel Treatment: To prevent fuel gelling, which mimics bad glow plug symptoms.

Frequently Asked Questions

Can I use starting fluid to help it start?

Never use starting fluid (ether) on an engine with functioning glow plugs. The ether can ignite prematurely from the heat of the plug, causing catastrophic engine damage or injury.

How long should I wait for the plugs to heat?

Most Polaris diesel models have a timer. Wait for the dash light to turn off before cranking. In extreme cold, you can "double-cycle" the key (turn on, wait, turn off, turn back on) to provide extra heat.

Don't Get Left in the Cold

Your Polaris Diesel is a workhorse, but it’s only as reliable as its ability to fire up when the sun goes down. If your machine is struggling with morning starts, it's time to stop straining your battery and fix the source of the problem. You can find OEM-spec Diesel Glow Plug replacements and electrical components for your Ranger at buywitchdoctors.com. Get your engine firing fast and get back to the job at hand.