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A really quick way to test if diesel glow plugs are working.

  • Andy.MacFadyen
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25 Nov 2019 09:01 #35298 by Andy.MacFadyen
This is a quick test to elimate gloew plugs as a cause of difficult starting of diesels in freezing conditions. All that is required is a decent multimeter that has a zero to 20v scale.

All that is required is to observe the drop in battery voltage while the engine is being "glowed" prior to cranking.

Assuming the battery is in decent condition and a reasonable state of charge even in freezing conditions after being parked overnightwe would expect to see around 12.4 to 12.5 volts When the glow plugs are operated and fuel pumps priming this will drop considerably. Even on a two electric pump system the fuel pumps will only draw about 10 amps total but the glow plugs will draw about 20 amps per cylinder. For a 4 cylinder this means a few of over 100 amps, this is enough to pull the battery voltage down below 11v possibly nearer 10v. When the glow plugs are turned off the battery voltage should recover fairly quickly to just below the voltage before the start of the yes.

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