Engine/Transmission (1998.5 - 2002) How do I tell if my heater grids are working?

[Silver Bullet Ram]

I am curious if mine are working. Mine seems to get louder as it gets colder out.

 

[B.G. Smith]

Watch the volt meter on first start of the day when outside temp. is well below 60 deg. The voltmeter will rise and fall as the heaters cycle on and off. bg

 

[Silver Bullet Ram]

so it has to be below 60 deg out then?

 

[Rattlin_Ram]

My voltmeter goes down for a few seconde, then back up, then back down. Also if I turn the headlights on, the dash lights get dimmer when the grid heaters cycle.

 

[B.G. Smith]

Heaters

so it has to be below 60 deg out then?

Yes, 60 deg. F is where they come on. I believe they are controlled according to the IAT (intake air temp). bg

 

[RKerner]

If you have the dome light on after you start the engine, it will really cycle dim and bright when the grid is working.

 

[dresslered]

I was curious when I first got my truck as well. It is true, that the headlights dim in phase with the heaters, but I rigged a couple of LED's on the center console to tell me when each was on. Initially (assuming right conditions), they both come on strong (180-amps). Then shortly thereafter, they alternate back and forth until the intake air is the right temperature or you achieve a certain road speed.

 

[Hohn]

The grid heaters will turn off above 17mph.



They have both the pre-start and post-heat cycles.



The pre-start cycles vary in length depending on temperature. They will stay on either 3, 10, or 30 seconds, depending on the temp sensed by the IAT.



Once the engine is started, they will continue to run at a short 5 second (or so) on-off-cycle until vehicle speed exceeds 17mph. You can see this cycling in the voltmeter and all vehicle lighting, as others have mentioned.



The post-heat cycle is there to not only reduce emissions, but to keep EGTs from getting too low when the engine is idling or loafing along. When EGT gets too low, you can get cylinder fouling, valve deposits, and cyclinder washdown (diesel fuel on the cylinder walls).