Preheating Glow Plugs

[15dci]

I've read that you can improve the starting of diesel engines on cold days by preheating the glow plugs by turning the key to ignition for a few seconds before starting. The Megane II doesn't have a key so does that mean we can't use this trick?

[petepete]

its cold enough in the mornings now to notice your car doesn't crank immediately on pushing the start button and waits until the heater plugs have done their job....

[15dci]

its cold enough in the mornings now to notice your car doesn't crank immediately on pushing the start button and waits until the heater plugs have done their job....

Ah, so the engine can sense how long to heat for? But does this mean that we are only able to use that automatic system or is there also a way for us to maually choose to heat the plugs for whatever period of time we choose?

[Wickydude]

Ah, so the engine can sense how long to heat for? But does this mean that we are only able to use that automatic system or is there also a way for us to maually choose to heat the plugs for whatever period of time we choose?

It's automatic. As long as all parts are in good nick you really don't need additional preheating. Are you having starting problems? If not, I'd forget about it.

[AlexB]

No need - these engines start without problems down to very low temperatures. The preheating interval is automatic and the glow plugs are also used under certain modes when the engine is already running. Preheating is a function of the coolant temperature, so it will take its time in winter. Most winter starting problems in the UK are caused by old and cheap batteries; use Bosch S5.

[Wickydude]

True, but glow plugs and glow relays do fail at times.

[15dci]

Ah, so the engine can sense how long to heat for? But does this mean that we are only able to use that automatic system or is there also a way for us to maually choose to heat the plugs for whatever period of time we choose?

It's automatic. As long as all parts are in good nick you really don't need additional preheating. Are you having starting problems? If not, I'd forget about it.

Yes I am having starting problems, typically it coughs and dies on the first 2-3 tries and then on the final try it seems to wait longer for the glow plugs to heat (the little dashboard coil light shows for longer) and then it starts. However it starts with very low and rough sounding revs and only after about 10-15 seconds afterwards does it kick into normal idling revs

[Wickydude]

I'd suggest changing the glow plugs. couple of tenners should be all for 4 new ones. They do wear down.
There could be other reasons for bad starting tho. low compression, camshaft sensor, fuel issues (filter, air in fuel lines) and a lot of other things I'm sure.

[petepete]

whip the wires off the glow plugs one at a time and dog 12v off the battery on - a small spark as you toutch it indicates its fine and just replace any that are not functioning...( if all heater plugs are ok you have other problems)

If you want the glow plugs to be on longer, take your foot off the clutch or brake just as the starter motor turns and repeat the starting sequence a second time.

[15dci]

That all sounds like great advice guys - many thanks I'll check the plugs as recommended and will also change the fuel filter as a first step.