Glow Plug Testing

Testing Glow Plugs

In today’s practical class we were shown a demonstration on testing glow plugs, this blog covers simple procedures on testing glow plugs for damage and if they need replacing.

A glow plug is a heating device used to ignite diesel engines.Diesel engines, unlike petrol engines, do not use spark plugs to induce combustion. Diesel engines rely solely on compression to raise the temperature of the air to a point where the diesel will combust spontaneously when introduced to the hot high pressure air.

Testing

With an ammeter:

Connect the ammeter in series with a glow plug and activate the relay, the current will spike to about 40 Amps and slowly decrease to about 15 Amps over a 3 to 5 second period.

If it's shorted the current will just go to 40 Amps and stay there because since the current is not flowing through the element heat build-up doesn't occur and current doesn't decay.

*We do not check for resistance when testing glow plugs because a faulty glow plug can still pass the resistance test.

With a power source:

We used a simple car battery and connected the positive lead to the thread of the glow plug and the ground cable to the terminal of the glow plug.

The element at the end should heat up from the top of the plug down to the centre, if it heats up from the middle or bottom then the glow plug possibly needs to be replaced. The image below shows the setup and heating of the test.