Should glow plugs receive any voltage while engine is running?

KYKub · Jan 9, 2016

Thanks for the replies. The machine is a Kubota G1900, 3 cylinder D722 engine. I posted in this area because I figured glow plug voltage would be pretty much standard across tractors. The correct key switch order is: 1) "lightning icon" which illuminates dash lights, 2) glow plug heat, 3) start/run.

Did some additional testing today. I have two G1900 machines so I checked voltage on glow plug operation on the second machine. 0 volts> turn key to glow plug heat position = 10V> start tractor = back to 0V and stayed there.

So, it seems that voltage should drop to zero volts during operation. It appears unlikely that thermoelectric effect would be present in one tractor but not its twin.

I let the engine run enough to get good and warm (on the original tractor in question) and monitored voltage to glow plugs. It dropped to 2.3V and seemed to stay there.

Would 2.3V indicate enough current to be concerned about?

Thanks again for the good replies.

skyhook · Jan 10, 2016

It all depends, if its been like that for a while, it doesn't seem to be hurting anything, but "I" would be concerned. As you found out, there should be 0 volts when running, these glow plugs take allot of juice and my concern would be battery drain. What made you decide to check their voltage?

PILOON · Jan 10, 2016

Low voltage vs the high suggests leakage of some sort. Could be as simple as a wet wire harness or corrosion.
While you can read a low voltage I bet there is minimal amperage.

To demonstrate an example, wet your fingers and grab the voltmeter probes in a low resistance setting and you will get a reading.

And yes battery drain could result over time.

zzvyb6 · Jan 10, 2016

"There is a timing module with 2 temperature inputs: ambient and engine. If the temps add up to a need for glow plugs, an indicator light comes on for up to 8 seconds. Glow plugs are lit and remain fully powered for up to 30 seconds to ensure the engine will remain running. When the engine reaches a preset temperature, the glow plugs are turned off."

Sounds like a few possibilities for you. A bad ambient temp sensor, a bad engine sensor, a bad timing module, wrong timing module (there have been 3 used since early models, or a retest in warm weather with the engine warmed up.