I am using an infrared temp Gauge, and I have an on board temp gauge, they are about 25-35 different. Which one should I go by? I am confused by this, as it says to read at glow plug, which the infrared is pointed right at it, and the on board is wrapped around the base of the cooling head. Any thoughts?

The onboard isn't the VST is it? That thing is crap. Mine will actually read as high at 600, but in general is about 50-60 off.

Also, make sure the E value is set properly on your infared if you can set it.

I just use a hand held one from radio shack and it works great.And if you have your gauge wrapped around the cooling head it should be much cooler then the inside of the head because that aluminum dissipates the heat fast.
shark

test the infrared to something.

like a cube of ice...

it wont be flawless since thats way off the operating range... but itll give a ballpark.

could do boiling water, not sure how infrared guns respond to a liquid though.

I doubt that boiling water would work well, since the emissivity would be so much different than non-polished metal. Same for ice.

To answer the question, I would guess that the IF temp gun is more accurate than the on-board gauge. You could test it by checking some large unpainted bolt (say from a picnic table etc) that is in the shade. That should give you a ball park figure as to how accurate the gauge is, profided you know what the correct ambient temperature is.