EGT question

[Pipewrench]

I have an Isspro EGT gauge. I noticed that when I am letting the glow plugs warm as the wait to start light is on, I see my EGT gauge climb and flutter a bit.
My other gauges (boost and tranny temp) don't do this.

I figured its not an electrical issue since the other gauges don't move.

So now for my question: Is the reading and movement I see on the gauge due to the heat of the glow plugs? Seems logical, just wondering if anyone else sees this or is something going on. Thanks in advance.
2002 F250

['01SilverBullet]

It could be heat from the plugs as there would be a very little bit leaking out an open exhaust valve, but I'd lean more towards electrical interference with the glow plug system, especially if the wire for the probe runs near the GPR or its associated wiring.

[Turbostang500]

X2. Won't rule it out but is very unlikely.

[Pipewrench]

X2. Won't rule it out but is very unlikely.

Won't rule out heat from plugs?

Another question I should probably know the answer to...do the plugs only fire up when its cold outside? Started the truck earlier and it was about 60 degrees....No movement or fluctuation on gauge.

['01SilverBullet]

I think they come on whenever you start it if the oil is below a certain temperature. If the engine is already warm and you go to restart it, they don't even come on (in which case I don't even wait for the light)