Are my glow plugs knackered?
 

I've noticed this winter that my S60 D5 has been a bit more reluctant to start in the mornings. Then this weekend, with an indicated -4'C on the DIM, it decided to start on somewhere between 3&4 cylinders; gave it a bit of boost and all was happy.

So I've got my multimeter out and tested the resistance of the glow plugs on 1,2,4,5; all showed as open circuit. Is it reasonable that the car would start with at most 1 good glow plug (I didn't test 3 as I wasn't convinced I was measuring anything real and it's behind the inlet maniford) at -4'C; or have I missed something?

The car's done 90,000 miles and is 6.5 years old so I'm not expecting the glow plugs to be in particularly good condition.

If they are open circuit, they must be bust. Their resistance should be very low when cold. On my old Vectra they were supposed to draw 10 Amps each, so at 12V that would around 1.2 ohms. When they warm up their resistance will increase but should never read as open circuit.

I believe they are supppsed to have a resistance of around 0.75 ohms at 20 deg C

You could also check out that a supply voltage is reaching them.

Thanks for the reponses. I realise they should have low resistance - but car is starting none the less (in some pretty obismal conditions) could it really do that with 1/no glow plugs?

Diesel engines didn't always have glow plugs, they technically don't need them, and the glowies are only active for about 30 seconds at most anyway. The glow plugs are there just to make starting much easier.

Diesel ignites spontaneously when under pressure and at a certain temperature (about 50 degrees C I think). The temperature to achieve combustion is largely generated by the act of sudden compression, but in a stone cold engine it would take a while for enough heat to build up to get combustion. The glow plugs simply speed up that process.

did you take the feed wire off each glow plug before you measured the resistance?
If so then they are no good with open circuit .
On modern direct injection diesels as your D5 Glow plugs only come on at very low temperatures . They do stay on pulsing for a while after it has started then for emission purposes ..

Define "more reluctant"

D5 here as well, and mine is also "more reluctant" but I'm also more reluctant getting out of bed in the morning too!

Outside of winter, she catches easily on the first turn.

Recently with the cold snap (extreme was -8) she caught around the 4th turn.
Glow plug indicator in Summer is on for less than a second. As said it probably didn't do anything just activated the circuitry then decided it wasn't required.

When it was -8 C the indicator was on for a good 5-10 seconds.
If you turn her off/then on again see how long the indicator is on the second time around, should be much less.

always going to take longer to start though as the initial compression heat is lost to the cylinder walls.

This is my third winter with the car, the first two winters there was no discernable difference in time taken to start the engine whether it was hot or cold (almost always on the first turn, except the one time I left it a little too long after the glow plug light had gone out). Now it takes several turns to start.

Not sure if of help, but this also seems like similar symptons to my injector problem, covered well on this site previously, the colder the weather the more reluctant it was to start turning over for several seconds ( i could count to 8 or 9)in very cold weather? First thing we did was replace glow plugs a couple not correctly working but made no real difference.

Not sure about the glowplugs but...... I have ben experiencing poor start from my S80 D5 in the recent low temperatures. All that I have read in this thread is very informing. However, I leave the ignition on for about 20 - 30 seconds before I start up and it fires up ok. Not tested the glowplugs but I soon will do. Cheers. Happy New Year.