Just wondering if anyone else has noticed this but on my 3500 DRW the fan for the heat/ac and also the head lights surge with the motor at idle, i.e. when the motor speeds up the fan speeds up and the lights get brighter, motor slows down fan slows down headlights dim. Nothing erratic very precise with the motor, Only at idle not while applying throttle.

JJ

 

Mine does too and I don't think it is an issue. Alternaters don't put out as well at low speed. Older vehicles don't change the idle speed as much as these do so you don't see the change except when you pull away.

 

Good to know

JJ

 

Grid heater working maybe? Does it when cold and first started?

 

This is all normal and it is the grid heater cycling. After 20 mpg moving the grid heater will not cycle. It will come back on if the air temperature at idle is not above a given level.