Testing Glow Plugs

[RichardM]

See my other post here in the thread about using Veg Oil http://forums.mud-club.com/viewtopic.php?t=46953&start=120
How do I test my glow plugs?  I assume that checking they are getting 12v when they should is not enough, do I have to check their resitance? If so what should it be?

[hairyasswelder]

are they 12v? If they are, take them out and put power to them... The tip will glow. If anything but the tip glows it has a short and needs replacing

Steve

[clbarclay]

Not sure what TDIs are like but on the VM its a pain to remove all the glow plugs so I just remove the connections to them and check resistance of each individal plug with a multimeter, which should only be a few ohms at most. If theres a lot of resistance or no resistance then its probably scrap.

[andyb]

Disconnect the wire to all the glow plugs. Then with the igintion on use a length of wire to 'briefly' connect each glow plug in turn to the positive terminal of the battery. A short spark indicates that the glow plug is drawing current and should be working. You only need to then remove and replace (or further test) those that don't 'spark' :)

HTH

[clbarclay]

The one trouble with that method is that it won't show up plugs that have either short circuited or like one of the plugs I've changed it was about twice the resistance so would still have sparked though didn't get as hot as it should have done.

[andyb]

True Chris....but you do need to know what resistance you are expecting. Not 'dis-ing' you method; still the most fool proof :)

[clbarclay]

I'm sure resistance is printed some where, I just assumed the majority were right and the odd one out was wrong.

[RichardM]

The Haynes book of lies recommends Chris's method of testing...check the resitance, should be a few ohms...but does say the only real way to know is to fit new ones.  It also says check that you get 12 volts for the time the light is on and a few seconds after...how long after depends on the ambient temperature.  I'll check mine this weekend, along with changing the oil and filters and greasing the UJs and prop shafts and any other jobs I find...