Q&A for How to Change Glow Plugs

To properly test a glow plug, understand that it functions as a self-grounding heating element where voltage is applied. Similar to any heating element, the resistance within the glow plug generates heat when current passes through it. Since resistance relates to amperage, the most accurate method to assess its functionality is by measuring the amount of current the glow plug draws. Checking for voltage alone at the glow plug is insufficient, as it merely confirms the presence of voltage and not the functionality of the glow plug itself. Instead, measuring the amperage the glow plug draws provides a reliable indication of its operational status.

Sometimes, when a glow plug fails, the tip may swell and expand. This can cause difficulties in removing the glow plug, as the hole it fits into may become smaller due to the expansion. In such cases, you may need to break off the tip of the glow plug to facilitate its removal. This can leave the broken tip in the combustion chamber, posing a challenge. There are two methods to address this issue. One approach, as outlined in military manuals, involves cranking and rotating the engine until the broken tip is expelled. However, this method carries the risk of damaging valves and cylinder walls. Alternatively, you may need to remove the cylinder head to extract the broken piece from the combustion chamber. When changing glow plugs, it's ideal that none of them have expanded tips that could break off, simplifying the replacement process.

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.

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.

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.

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.

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.

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.

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.

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

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.

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