I noticed this issue when I start my truck cold (I haven't really noticed if it does this warm). When at idle with heater and lights on, the heater seems to slow down speed up, almost like I am changing fan speeds and the lights keep going dim then bright then dim, etc. I noticed the amp gauge keeps fluctuating as well when it does this. Does this mean I need a new alternator? Thanks for the help.

 

Nope your alternator is just fine. What is happening is the air intake grid heater is cycling, thus putting a load on your alternator and causing the lights to dim and gauge to drop. It's completely normal and every 1st gen does it. I believe the grid heater comes on when it is colder than 50*F(correct me if I'm wrong gurus ).

 

Thanks for the quick reply. I am a bit relieved I don't have to replace the alternator as it has been in the 20's here lately and I don't feel like working on the truck.

 

I've heard stories that the fluctuating voltages can take out aftermarket radio headunits...

My Pioneer unit seems not to really care, though. Anybody remember those stories?

 

Those grids must suck a tremendous amount of power to produce what looks to me like about a 4-5 volt drop from a running 120 amp alternator. It's hard to tell with that excellent, easy-to-read OEM gauge. I leave everythging including the headlights turned off for the first mile or so down the road. I can get away with that around here because there's literally no traffic on the road when I leave for work at 0500. Probably won't hurt much, but not a good idea to unnecessarily subject stuff like stereo equipment to that voltage fluctuation.

 

i just noticed the same thing in my truck, and knew it was cold related, just didn't know how. Thanks.

 

Here is something I posted a few days ago on anothersite that might help out here.


Here is the cycle time for the heaters from the Dodge manual.-

PREHEAT, BEFORE START CYCLE
Above 59 degrees F does not activate
18 degrees F to 59 degrees F Cycles for 10 seconds
1 degree F to 18 degree F Cycles for 15 seconds
-15 degres F to 0 degrees F Cycles for 17.5 seconds
below -15 degrees F Cycles for 20 seconds

POST HEAT, ENGINE RUNNING CYCLE?

Above 59 degrees F No
18 degrees F to 59 degrees F Yes
1 degree F to 18 degrees F Yes
-15 degrees F to 0 degrees F Yes
Below -15 degrees F Yes

I cannot find how long the post heat cycles are.
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I believe the post heat cycles go until the engine temp gets to a certain temp, whatever that is. It quits long before I have hot heat.

DP

 

It's just time based on a 1st gen, the computer is pretty stupid. I'm doing 55 mph when mine quit cycling in the morning.