Any scientists around?
 

1) The resistance of the GP is so small, < 2 ohm, I doubt the temperature will make much difference or measurable using our home DVM. Unless you have a scientific resistance bridge to measure very low resistance.

2) When 12V is applied to the GP, it will heat up instantaneously, in the order of milliseconds. I really cannot see any difference when the 12V is applied at -32F, 0F, 75F or whatever. The amperage drawn would be almost the same at any temperature.

If the GP is open circuit or bad then just replace it and be done. Battery will make a difference as per the 'cold cranking' power. If it doubt, replace it also. No harm done.

See the Chart below. the Brown line is the Bosch Glow Plug.

It appears there is a few seconds when no heating at all goes on.

In the Chart it takes about 2-3 seconds to reach 600 degrees C what they say is the minimum starting temp.

This is consistant with what I observed; the Glow Plugs pulled high amps until the Plug got hot and dropped down to 16 steady amps and that took about 2 seconds (that is the bare Glow Plug out of the Engine at about 75 degrees F).
Also I had the full 12.50 Battery Volts going to only one Glow Plug so I would supspect that one Glow Plug would heat faster then if there where 5 Plugs and a Glow Plug Relay draining the Battery.

I have no reason to believe that a Glow Plug acts any different than any other Electric Heater when faced with a Colder Temp. The colder it is the longer it takes to heat up the area you want heated. And, -10 degrees F is plenty cold.

It got pretty cold here in the valley on Saturday.
I didn't know it got that cold in Long Beach! Whoah :eek:

Assuming the heat up is linear and it takes 3 sec to reach from 0C to 600C ( It is not shown in the chart, it is by extraplotion. ). How long it takes to get from 30C to 600C, instead of from 0C? It would be 2.85 second. So it would be about 3.10 sec or less to heat from -10F to 600C. I would not worry about that .10 second. As I have said, it is in the order of milliseconds to climb from -10F to 75F (ambient). I would not even take it into consideration for GP.

You will need to question Bosch on the details of their Chart.

What there is of the Chart clearly shows that the Glow Plug Heat is not instantaneous to the extent that it reaches the minimum starting instantaneously; and in fact takes quite a few seconds to get up to the Minimum Starting Heat.

I think the chart would have been more interesting if did show what temp the test was done at.

Yes, I Ice Skated to Catalina Island and back on the Ice Bridge.:)

It's undoubtedly true that ambient temperature doesn't make an appreciable difference in how quickly the tip of the glow plug reaches 600C, but the tip is just the tip!

The goal is to heat the pre-chamber to aide in ignition. First the glow plug has to heat the ambient air around the glow plug tip, then the air heats the metal of the pre-chamber. At -10C, all of that air and metal is going to be noticeably slower to heat than at 30C.

Using the toaster analogy, at -10C the heating elements in the toaster heat up almost as quickly but the frozen bread will take longer to toast than room temp bread.

I really do not want to venture anymore into this subject. I am talking about the time it takes for the GP to reach temperature whether it starts at -10, 0 or 75. How much air volume it needs to heat up will be relevant but it is a function of the sensor and the battery. You can heat/glow the chambers with the battery all day long for all I care, as long as the battery can sustain it. What I am getting at is the 'scientists' comments on initial current drawn in those spit seconds. It is not significant in the grand scheme of thing. The resistance of the GP at -10 is not relevant either.

Your analogy

"The bread will eventually be toasted if you have enough electricity, or battery. It is not a function of the heating element if it is in good condition. Nor at what ambient temperature the toaster was turned on."

Enough said.

I think what is missing is that the Cold Glow Plug has a Different resistance than when the Glow Plug is fully hot. And, it takes more Current/Amperage when the Glow Plug is Cold than it does when the Glow Plug is hot.

This was an observation from and actually test.

The speculation part was that if the Carbon acts as a conductor into the Cylinder Head and on to the Coolant the Glow Plug is going to stay cooler longer and draw more Current/Amperage longer.

I further speculate that drawing higher amps for longer periods shortens the life of the Glow Plugs.
The Mercedes Manual has that the Carbon Build up shortens the Glow Plug life but does not say the mechanism that causes the shorter life.