Glow plugs - should you change all of em??

[dave_s13]

Now then, it were chuffin cold this morning and I had to instruct my wife over the phone on how to get the car started (engine top cover off, half kettle boiled water over the injectors). This works fine so I'm pretty certain it's one or all of my glow plugs that's goosed rather than an injector issue.

Now, this is my first deisel car that I've had [minor] issues with (Volvo V70 D5) and I was a bit miffed to see that an NGK plug retails at £14....x 5 = a lot!

I was just wondering if there is a reasonably straightforward way to identify if it's just one plug gone, all, or just a couple? Or is it just usually better to change them all together? It's not a break the bank amount of cash but I'd rather spend £14 than £70, especially as I just had to spend money on 10litres of ATF (£110 quid!) and it'll need new front tyres in the next month or so.

Oh and another really rather daft question......where are the glow plugs on a volvo D5 engine located? >runsandhides<

What you lot reckon?

[jatinder]

I think you just connect to the battery, but it really depends on the age and millage of the car, I would just change them all for piece of mind.

No point changing one at a time every couple of months.

[Classic Grad 98]

TEN LITRES of ATF?

[orhan]

Do not just connect to battery some ecu controlled and only 5volts and it is best to change all at the same time. Do you only change some of your petrol engines spark plugs at service or all is the best way to put.

[dave_s13]

Classic Grad 98 said:

TEN LITRES of ATF?

Yep.

The transmission doesn't actually hold 10litres.....that's just the amount needed to flush it through sufficiently to clear the old crappy fluid out of the box. It's was a bit of chore but has improved the gearbox operation hugely.

Car has done 125k miles by the way. I was going to sell it but no interest, decided to lavish some TLC on the thing and keep it for a while longer. It's a great car.

[Mr2Mike]

orhan said:

Do not just connect to battery some ecu controlled and only 5volts

No they aren't. They are all powered from the vehicle battery via a relay (which is almost certainly controlled by the ECU).

Edited by Mr2Mike on Wednesday 1st February 14:25

[thinfourth2]

Look at how hard they are too change as you might find you are better off doing them all at once

[Jimmyarm]

Unless you have all four gone its much more likely to be an injector issue. Some of the modern high pressure diesels don't have glow plugs at all.

Glowplugs don't need to be replaced in sets, they don't have any specific lifespan like sparkplugs.

As above it depends on how hard they are to change, if you have to take half the engine apart to get to them then you might as well do them all. This seems the case seeing as you can't see them.

I'd take it to a diesel specialist and spend some money on getting the plugs tested and if they are ok a leakoff test done on the injectors which will probably reveal one or more of them is dribbling.

You could also have a small air leak in any one of the many pipes on the system which is allowing a small amount of air in overnight causing poor starting.

Unfortunately modern diesel engines are fairly hard to diagnose faults on without specialist equipment and a good knowledge of the injection system you are looking at.

[buggalugs]

You can check their individual impedance, none of them should be open or short circuit. Check you get 12v to the rail at cold key on too.

[dave_s13]

Thanks chaps.

Riddle me this though.

Given the car starts perfectly fine in warmer temps, even when left overnight, does that not point a big pointy finger at my glow pugs rather than other much more bd expensive things that I don't want it to be?

Tell me it is so.

[buggalugs]

You could take a guess that that's the case but testing them is the answer really!

[mcford]

If you remove the glow plugs, the non working ones will be covered in soot and look distinctly different from the working ones.

Mr2Mike said:

No they aren't. They are all powered from the vehicle battery via a relay (which is almost certainly controlled by the ECU).

Edited by Mr2Mike on Wednesday 1st February 14:25

The glow plugs in some of the modern VW engines are designed to work at less than 12 volts, in some of their technical literature there are warnings against supplying them with 12 volts as they will melt, not something that you really want to do with the glow plugs fitted.

[Billy_rfc]

dave_s13 said:

10litres of ATF (£110 quid!)

Jesus, what spec was that? Seems well pricey.

[dave_s13]

Billy_rfc said:

dave_s13 said:

10litres of ATF (£110 quid!)

Jesus, what spec was that? Seems well pricey.

It's this stuff
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...

That chap did me 10litres delivered for £110....cheapest I could find.

Mobil ATF JWS 3309

You cant use anything else other than 3309 spec oil or it lunches the box.

Anyway, back to my glow worms. I am tight so only bought 3 new ones on the way home. I found 2 that were reading 0 ohms and they did look a bit ropey so changed these out and stuck the other one in for good luck.

It's going to be cold as chuff tonight so we shall see.

[Eggman]

What were the resistances of the good glow plugs like, out of interest?

[dave_s13]

I used this guide

http://www.ngk-dpower.com/index.php?id=31&L=2

Not sure what the figures were as my multimeter is very st and needs a new battery. I just found that 2 of them read zero.

[thinfourth2]

dave_s13 said:

I used this guide

http://www.ngk-dpower.com/index.php?id=31&L=2

Not sure what the figures were as my multimeter is very st and needs a new battery. I just found that 2 of them read zero.

Should never read zero unless you have a short

Easy way to check

Remove the bus bar/wires from glow plugs

Get jump leads

Attach positive jump lead to battery positive

Tap the connection of each glow plug if you get a spark it is probably okay


This might not be a good idea in a car with a sensitive brain

[dave_s13]

I think on my multimeter, which is out of Christmas cracker and needs a new battery, is fked. Basically 2 of the plugs read 0 and the electrodes were very burnt looking. The others gave random readings bouncing about all over the place.

Anyway we'll see in the morning if I've chucked out the good ones and put 2 knackered ones back in :-)

[chris1roll]

mcford said:

The glow plugs in some of the modern VW engines are designed to work at less than 12 volts, in some of their technical literature there are warnings against supplying them with 12 volts as they will melt, not something that you really want to do with the glow plugs fitted.

I don't know about modern systems, but older ones they were wired in series, so on a 4cyl each one would be 3 volts. Also if one fails the others won't work.
The reason I am acutely aware of this is when working on our old tractor I hadn't twigged this (in fact on that they were wired in series with the indicator which was basically another glowplug behind a mesh screen on the 'dashboard') and decided to test one on its own by applying 12v to it. Pop!! Just glad my face wasn't too close to it when I did it!

[Eggman]

I think it's more usual for them to fail open circuit - if they shorted to earth then all of your glowplug wiring would go up in smoke.

(As mine did quite spectacularly one afternoon, when I unthinkingly tried to start the engine after damaging a glow plug. Doh!)