Testing Coolant Glow Plugs

I have a few questions about the coolant glow plugs:

1. What are the standard operating parameters for the coolant glow plugs? When do they operate and under what conditions?
2. How do I test whether they are working?
3. How critical are they for a car in a temperate climate like Southern California? Are they worth messing around with?

They are not a critical part of the ALH tdi system. Basically they come on when the intake temps are below 30F and run until the engine gets to about 130f.
Lots of good info here:
http://forums.tdiclub.com/showthread.php?t=269731&highlight=coolant+glow

They are basically ordinary glowplugs (albeit from the earlier ID engine) and you test 'em the same as any glowplug; with a multimeter. They should read 0.8 - 1 ohms each.

They are activated by a combination of low coolant temperature *and* low ambient temp, as measured by the IAT built into the MAP.

All that said, save yourself some time, cause:

garciapiano said:

How critical are they for a car in a temperate climate like Southern California? Are they worth messing around with?

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In southern CA... I would say absolutely not. Many many folks in the frozen Great White North don't even know theirs are broken.... they have only a very modest impact on warm-up time.

dont bother with it, they are basically useless and just really to help with emissions when the car was made.

Mongler98 said:

dont bother with it, they are basically useless and just really to help with emissions when the car was made.

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Not entirely useless, they do help bring coolant temp up quicker and they do work if the system is functioning properly.

I'm glad mine work...

Steve A

Steve Addy said:

Not entirely useless, they do help bring coolant temp up quicker and they do work if the system is functioning properly.

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Agreed, and there's a couple threads here documenting their performance in terms of improved warmup times.

That said, the system does not engage unless both coolant temp and IAT are -5C (23F) or thereabouts initially... would not expect that to happen too many days in So Cal and thus probably not worth a lot of time to fix 'em?