Diesel glow plug switch

[Piwoslaw]

I recently read an article advising diesel owners to "double start" on cold mornings. "Double starting" means to turn the key to 'ON' so that the glow plugs come on for 1-3 seconds, then back to 'OFF' and immediately 'ON' again, only then to start the engine. This is supposed to double the amount of cylinder preheating by the glow plugs.

This got me thinking whether to hack a switch to manually turn on the glow plug relay, allowing me to do the same (or more generally, to better control how much longer the glow plugs work) without fumbling with the key in the ignition.
This should be a momentary switch/button, so there is no risk that the plugs stay on by accident.

Any opinions?

[cRiPpLe_rOoStEr]

When an uncle of mine used to own a Suzuki Vitara adapted with a Volkswagen 1.6D engine, the glowplugs were controlled by a switch.

[freebeard]

The Dasher diesel had a light that went off after IIRC 15 seconds, then you'd push in a button.

[Piotrsko]

Since I always double heat the F250 when there's snow on the ground, I say go.for.it. turning the key off and on seems like such a waste, but my system apparently leaves them on for a bit after it starts. Current one shot system doesn't help with the start, but smooths idle enough to get to the corner without stumbling. Otoh watching the ampmeter showing 90 amps drain is a bit scary and I eat alternator output bolts. Apparently it doesn't charge with the glow plugs heating, some sort of delay programmed in. I get all the way out to the major cross street before the amp gauge goes to charge. Does give me 4 cold starts and 10 miles driving before the batteries die.

All the high altitude cold weather classified school busses I drove left them on for a while also, according to the dash light.

[cRiPpLe_rOoStEr]

Originally Posted by freebeard

The Dasher diesel had a light that went off after IIRC 15 seconds, then you'd push in a button.

So the glowplugs were turned on with the key, and then you had to push the button to turn the starter on like a motorcycle? Or did that light indicated when some capacitor was energized to provide power for the glowplugs?

[Piotrsko]

Glow plugs are a high current electrical resistance heater. Even massive quantities of super capacitors don't hold enough energy to get them warm enough to start on a 0C morning.

In my case: excess of 5.4kw for the 5 minutes they are on

[freebeard]

So the glowplugs were turned on with the key, and then you had to push the button to turn the starter on like a motorcycle?

Thought I'd answered this last night.

IIRC, pull out the control, turn on the key and wait for the light to time out (15 seconds IIRC). I think the manual went with the car.

[Piwoslaw]

So I searched some more and came across that the more on time, the faster the glow plugs will burn out.
And that any fuel saved with extra glow time is more than lost in the cost of replacing them.

This was an argument to prove that glow plugs should only be on as long as required to start the engine, with no benefit from more pre-heating than the bare minimum.

[Piotrsko]

Can't advise on glow plug life, mine in the F250 have lived for 25 years in high altitude cold winter (-20C) environs, 13 years on the TDI, both are daily go to work drivers stored outside Eaten a couple controllers, bunches of batteries, and mildly unsure if the computer or controller monitors failures. Suspect not.
I do know school busses need to crank longer when a glow plug fails, and when they do start run like crap until you get cabin heat. Some times it is a race to start before the battery dies.

[cRiPpLe_rOoStEr]

So, most likely a grid heater could be a better choice.