How do you test a glow plug?

One way is to take it out, connect it to a 12v battery, and see whether it gets hot. Glow plugs take a high current (40-50A) so be careful with connections - connect one wire to the battery before connecting to the glow plug, then do the same with the second wire.
 
The quickest way is to remove the glowplug from the head, attach a set of jump leads (neg to body, pos to threaded connector) wait 7 seconds and remove jump leads. If the glowplug is functioning it should have got cherry red while connected.

WARNING - be careful that you don't:
a) short the jump leads
b) burn yourself
c) burn the boat
d) leave connected for too long causing damage to glowplug
 
No need to take it out. Disconnect the wiring and check it with an ohms meter. If its Ok it will read zero ohms if its burnt out it'll give no reading.

Better and the method I use to check them in the car. A 12 volt bulb on a couple of leads (I use an old headlamp bulb) connect one lead to the battery the other to the glowplug (wiring disconnected of course). If its Ok the bulb lights if its burnt out it does not light.
 
Quite right, but I'd somehow assumed that someone who didn't know how to check it most probably wouldn't have a multimeter. /forums/images/graemlins/tongue.gif
 
WOW, be careful! Besides the high current and heat issues already mentioned, some glowplugs are not 12v on 12 engines, becuase they are connected in series. In such a case putting 12v across it will kill it!

Test plug with with ohmeter, and engine wiring with volt and ammeter.

Anthony
 
You're absolutely right, Anthony, some multi-cylinder engines do use low-voltage glow plugs wired in series. But, you know, with most queries which crop up on these forums very few people give a thoroughly comprehensive and pedantic answer because, in many cases, it's only likely to confuse. So when a guy with a Sadler 26 with a Volvo Penta engine asks about his glow plug, I tend to think "Ah, Sadler 26, probably single cylinder, and he said glow plug (not glow plugs), so it'll be a 12v plug". Then again, how many Volvo Penta engines with multiple glow plugs use other than 12v plugs? /forums/images/graemlins/wink.gif
 
take it out, hold rounded end between thumb and fore finger, connect wires to battery and connect to glow plug, if you yell "oh [--word removed--]" and drop it its working OK!!
hee hee hee!!
/forums/images/graemlins/laugh.gif
 
i had a pedantic twat on a post years ago, same thing, most engines use 12v but some mercs were cited as series engines, most unlikely nowadays because if one blows the lot stop working.
stu
 
[ QUOTE ]
i had a pedantic twat on a post years ago, same thing, most engines use 12v but some mercs were cited as series engines, most unlikely nowadays because if one blows the lot stop working.
stu

[/ QUOTE ]I wouldn't go so far as to call hm a "pedantic twat", but I do think his time would be better spent applying a spell-checker to his website! /forums/images/graemlins/wink.gif
 
"most unlikely nowadays "

Maybe so, but the OM636 has series plugs (3.6V IIRC) and a ballast resistor, unless you have had to change them to modern 12V plugs, like I had to last year.
 
Oh, i wasnt referring to present company but i agree, an amateur front page and then flashy un spell checked flash with irritating music that my daughter played hell about because when it launched it drowned out the news on the box!
hey and my new years resolution was to not go winding up fellow forumites!!
 
perhaps wrong choice of words, not a mainstream practice in the engines used in the vast majority of AWBs maybe? But you see when one starts to nit pick one opens oneself up to being called pedantic?
 
Most people check that their glowplugs are OK by watching the amps and/or volts when switching the heater(s) on in situ. If not, turn on a tungsten type cabin light and see that the lamp dims. I wouldn't remove a plug unless it failed that simple test, or I was in last resort territory.

Tell us more about the starting problem. What is the engine like when running? Clean exhaust, good power, sounds normal?

Are we talking about cold starting? Assuming that there are absolutely no fuel leaks whatsoever then the most usual reason for poor cold starting is a weak battery or bad battery terminals and wiring. This wiring deteriorates with time - it is NOT 'fit and forget'. Listen for speed of cranking - most diesels need a pretty fast crank speed. Maybe you need to test your start battery. It could be that your battery isn't being kept fully charged when you come to start.

Otherwise, poor compression is a common cause of poor starting in an older engine but if you needed to ask how to test a plug I think you ought to get a mechanic to look it over for you if that seems to be the problem.

Plug failure is possible but test that without removing it and look elsewhere for your starting problems.
 
The ampage quoted seems somewhat high for a single glow plug which is what you would be testing off a battery. I seem to remember on my Trooper the glow plugs had a resistance of about 1 Ohm each which means they would pull about 12 amp per plug, 48 A for 4 plugs wired in parallel (On the Trooper, don't know how many cylinders on the engine in question)
 
[ QUOTE ]
Most people check that their glowplugs are OK by watching the amps and/or volts when switching the heater(s) on in situ. If not, turn on a tungsten type cabin light and see that the lamp dims

[/ QUOTE ] The current drain would be a good thing to know but for a multicylinder engine (at least multi glowplug) it'll be impossible to tell if just one plug has failed by looking at a light dimming or even, with certainty, the voltage dropping.

I have car that consumes glowplugs for some reason. I know the symptoms of a failed one only too well. Difficult to start when cold, eventually starts and runs unevenly on three cyls until the fourth cuts in. First thing I do when that happens is whip the wiring off and test them with a lamp. Not only does that confirm the problem but identifies the dud one.
 
[ QUOTE ]
I have car that consumes glowplugs for some reason.

[/ QUOTE ]Have you thought of putting a resistor in series? Most probably the engine was designed to start at -15C so you might get away with a lower current.

<span style="color:blue"> Edit:- Second thoughts...might be that they are of shoddy mechanical design and just break while engine running, so putting a resistor in series wouldn't help. You might do better finding an alternative source for the plugs </span>
 
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Second thoughts

[/ QUOTE ] Tried several sources. Manufacturers parts fron dealer, Lucas one from local spares shop and Halfords own. No difference. I think the problem lies elsewhere, but I have taken the easy option and just replace them when they fail. Probably now got 3 out of 4 on the 5th set. Just waiting for the fourth one to go!
 
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