How to Change Glow Plugs

Co-authored by wikiHow Staff

Last Updated: August 12, 2020 Approved

Diesel engines are designed different than gasoline-based engines. One of the most significant differences is diesel engines have glow plugs instead of spark plugs. Spark plugs create a spark that ignites the fuel to power the vehicle. Glow plugs rely on compression rates to raise air temperature to the point of spontaneous combustion of the diesel fuel. To save money, here are a few tips on how you can change your own glow plugs.

Steps

1
Find the glow plugs in the engine compartment.
- They are usually on top of the cylinder head.
2
Remove the glow plug wires.
- The glow plug wires are beneath the engine's valve covers. You will find one end attached to the top of the glow plug and the other attached to the engine. Remove the wire attached to the glow plug. Remove the small nut that holds the wires to the glow plugs with a wrench. Push the wire aside. Repeat this process to remove each glow plug wire.
3
Remove the glow plugs carefully, one at a time.^{[1]
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- Loosen each glow plug from their sockets using a ratchet.^{[2]
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4
Clean each electrical contact and nut.
- Similar to battery contacts, glow plug wires can become dirty, which can result in a poor electrical connection.
5
Use reamer and ream the glow plug hole for each glow plug.^{[3]
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- This is just to clean out the glow plug hole, so ream only long enough to remove any buildup.
6
Replace each plug and tighten them down with a ratchet.
- Tighten them just to the point of slight resistance. If you tighten them too much, the next time you need to change the glow plugs you might break one off trying to remove it. This can result in a costly repair.
7
Reattach the electrical wires to each glow plug with a nut using the wrench.

Community Q&A
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Question

Can I change glow plugs myself?

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For most vehicles, yes. You just need to make sure you have the right kind of glow plugs for your car, as well as the appropriate tools, such as a manual torque wrench.
Question

How long does it take to change glow plugs?

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It can take anywhere from an hour to about 5 hours, depending on the complexity of your engine. It will take longer if your vehicle has valve covers or other parts in the way that you have to remove.
Question

How much does it cost to replace glow plugs?

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If you do it yourself, it probably won’t cost much more than $65-$70. If you have it done professionally, the price may be closer to $300, including parts and labor.
Question

If one glow plug stops working, do I have to replace all four?

Community Answer

Generally glow plugs are replaced as a set of 4; if one stops working, it is generally time the others may start to fail. You can get a set of 4 very cheaply, and will save a possible breakdown when the car fails to start on a cold morning.
Question

What are the symptoms of worn out glow plugs?

Community Answer

If you don't get a dashboard alarm telling you a glow-plug is out, then the car will need a few cranks to start, particularly when cold. It will start more easily when it's hot. If you lose three plugs in a four-cylinder engine, then the last plug may not start the car on its own, although two plugs usually will.
Question

How long do glow plugs last?

Community Answer

Typically, three to four years. They just fail, though, rather than wear out, so you can't see whether a glow plug is in good shape or not just by looking at it.
Question

Why will my heater not work after I changed my thermostat?

Community Answer

There is air in the system that must be bled out. Check to see if the radiator is full after running the engine. Keep filling it a few times if needed. Remember not to put cold water in a hot engine, this could cause severe damage.
Question

Why does my diesel engine keep running when I turn the ignition off?

Community Answer

If it runs for between 30 seconds to a few minutes, then your vehicle is probably fitted with a turbo timer.
Question

What do I do if my glow plug is frozen in place?

Community Answer

You'd be best off leaving it alone, and relying on the other three to start the engine. If you break it, you could face an expensive repair. When replacing the others, do not over tighten to avoid similar problem in future.
Question

I changed my glow plugs, and it runs good, but some smoke is coming out. Does it need to be calibrated?

Community Answer

Sometimes oil leaks into the cylinders and burns off. If your oil gets low frequently, then that is the case.