Glow plugs

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Daydream believer

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My Volvo Penta MD 2020 D is coming up to 10 years old & possibly 3000 hours use. (Hour meter packed up at 1250 hours).
Suddenly starting has not been its usual instantaneous fire up unless I hold the glow plugs on for 30 secs instead of the usual 10 secs
Exhaust is still clean. Engine runs perfectly with full power once up & running. Situation is same for hot as well as cold
Question
How often do I need to change glow heaters?
Is it a standard service item or should they last as long as the injectors
 
Daydream believer said:
How often do I need to change glow heaters?
Is it a standard service item or should they last as long as the injectors
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To all intents and purposes. I'd liken glow plugs to light bulbs - they only need replacing when they stop working. Unlike injectors, there's nothing to adjust or service on a glow plug; they either glow, or they don't.
 
There are 3 glow plugs. ??

Maybe just one has failed. Certainly worth checking them. They have a very low resistance if Ok and are open circuit when failed

When my car gets difficult to start i know a glow plug has failed. (For some reason it eats glowplugs) I just check them and replaced the failed one.

I disconnect the wiring and test them with a bulb on a couple of leads.
 
As VicS says, either the gloew plugs work or they dont. The buklb test isnt qute 100%, as very rarely (I have never actually seen it) they can short internally. But as they nearly always go open circuit, its a pretty good indicator.

But you should not need glow plugs for a hot start, there is something else wrong. Could be mechanical, could be fuel related. If it has happened suddenly, this suggests a fuel fault - injectors, air leak, partly blocked filter, or faulty pump(s). Quite often the lift pump can cause starting problems as it fails to deliver enough fuel to the injector pump until the engine is running at idle speeds. A valve not closing completely causing low delivery, or pin hole perforated diaphragm will cause no end of grief!
 
Daydream believer said:
Vis S
Can you elucidate please re bulb & wires & how
Cheers
Click to expand...

I take the wiring off .

I have a bulb, old headlight with only one good filament, on a couple of long leads I clip one wire on the battery positive then touch the other wire on the top of each glowplug in turn.
If the bulb lights its OK if it doesn't the plug is O/C

( it'd be a bit more complicated with two-wire glowplugs and an isolated negative return and an earthing relay but still possible to use the same idea ... just need to connect the negative sides back to battery negative as well)
 
VicS said:
When my car gets difficult to start i know a glow plug has failed. (For some reason it eats glowplugs) I just check them and replaced the failed one.
Click to expand...

Vic, know the symptoms precisely! However as they age the resistance of the plugs does seem to increase very slightly, so if you just replace the dud glow plug it takes a disproportionate share of the current due to the resistance inherent in the wiring upstream. Hence .... etc.
 
I was reading an old copy of PBO the other day and it touched on a possible glow plug problem which I believe was with Volvos. It is possible for the hole through from the plug to the combustion chamber to coke up and the manual suggests the suitable size of drill bit to be twiddled through by hand to clear it. May not be relevant, but then again it may...

Rob.
 
VicMallows said:
Vic, know the symptoms precisely! However as they age the resistance of the plugs does seem to increase very slightly, so if you just replace the dud glow plug it takes a disproportionate share of the current due to the resistance inherent in the wiring upstream. Hence .... etc.
Click to expand...

I have had this car for a about 16 years . Failure of a glowplug is a common occurrence .. at least it was when the car was in daily use.
many times I have just replaced a failed plug.

Once I replaced the whole set to no discernible advantage. Over time I subsequently recycled the three good plugs until they in their turn failed.

With four functioning plugs, regardless of their relative age, it always starts straight up. You can hardly call it cranking

Also replaced the control relay once ... £70 for no benefit.
 
ghostlymoron said:
I don't think my Yanmar has glow plugs. How come it starts so well?
Click to expand...

Correct, Yanmar do not use glowplugs. They have a mechanism for cold starting which allows you to advance the fuel rack beyiond its normal full position giving an ectra charge for starting. The linkage reverts to normal once the engine fires. Your engine also starts nicely because it has good compression, no fuel/air leaks and you're lucky!

My Mitsubishi based engine starts well without using the plugs most times, but doesn't pull enough revs under load. Running problems are different - I believe mine is coked up...

Rob.
 
rob2 said:
Correct, Yanmar do not use glowplugs. They have a mechanism for cold starting which allows you to advance the fuel rack beyiond its normal full position giving an ectra charge for starting. The linkage reverts to normal once the engine fires. .
Click to expand...

I've seen this statement before in this forum, but when I had a 2GM20, there was no mention of it in any manual that I saw.
Some Volvos do have this overtravel mechanism I believe.
My Yanmar was a very good starter on any day that I would consider sailing, but on the rare occasions I started it in the coldest depths of winter, it could be a bu**er to get going.
My present Beta needs 5 to 10 seconds heating for the first start of the day, instant at any temperature, but no heating for subsequent starts, which is why I question whether the OP's Volvo has a heater problem.
 
In the manual for the Volvo Penta MD2020, which we have. It states that the GLOW plug must be operated even if the engine is hot. It also states that a 10 second press is enough. However sometime my Starboard engine alarm does not go so I hold it for a few seconds more before firing up.

Peter
 
Cold starting the Yanmar 1GM10 (no glow plug) is a doddle. Activate the decompressor, spin the engine up (2 or 3 revolutions should be enough), drop the compressor. This gives a wee bit of extra fuel in the cylinder and is much easier on the battery. As long as the throttle is set properly mine starts every time. This system used to work with my old MD1b, too. I don't think it had a glow plug either. If you need to use the glow plugs every time you start, I think you might have a problem. Low compression (try the handle) or else fuel pump/injector wear (when were they last serviced?).
 
VicMallows said:
Vic, know the symptoms precisely! However as they age the resistance of the plugs does seem to increase very slightly, so if you just replace the dud glow plug it takes a disproportionate share of the current due to the resistance inherent in the wiring upstream. Hence .... etc.
Click to expand...

Mr ohm and his law has me thinking otherwise... The new one is only going to take as much current as it needs, you can't force current through.
 
rosssavage said:
Mr ohm and his law has me thinking otherwise... The new one is only going to take as much current as it needs, you can't force current through.
Click to expand...

I specifically mentioned the (inevitable) 'upstream' resistance. This will be common to all the glow plugs in parallel. There will be a voltage drop due to that resistance. IFF the new plug has a slightly lower resistance than the older plugs it will take slightly more current than the others.

(all a bit academic and probably not worth worrying about ...... my BUKH 20 does not have any glow plugs and starts fine :) )
 
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