Was wondering if it is normal for the charging system to be on the low side at first start? Never really noticed this before. The gauge normally shows a charge of over 14 volts, but in the mornings and afternoons when the truck is cold the gauge will stay to the left of 14 volts i guesstimate 12. After a couple of minutes it will return to normal. The motor seems to really rattle when it is below 14 volts, and when it returns to normal the truck seems to come to life and quit rattling. The temp here today was around 50°. does this have to do with the grid heaters or have I got other issues? Hopefully one of these days I will be knowledgeable enough to help someone!!

100% normal. The alternator has to replenish the "juice" from you starting your "Cummins" up!!! That's all. It shouldn't take too long. As long as she comes back up in short order, you've nothing to worry about!!!!! IMHO anyway!!!! Later!!!

If it is just cycling up and down between 12 and 14 for a couple of minutes it is the grid heaters cycling. Perfectly normal. Keep hanging around and you will help someone. I came here with nothing but questions, but now also have answers. Thanks to all the folks here. If you read alot of the threads here you will see alot of us asking questions, so dont let that bother you at all.

The guys are right its the grid heaters doing there job...Now to explain it a bit more. The grid heaters draw 195 amps pre-heat and then 95 Amps post-heat and everytime the grid heaters kick in it pulls really hard on the alternator giving that rattling sound. Grid heaters are use at temps below about 60-65*F. So enjoy the Cummins its doing its job...

as everyone else said, its normal. mine does it as well.But when you see them stay down like that you have a stuck solenoid that will do some damage if not caught quickly. one of mine was dead and the other stuck closed even after keys were out. Almost burned the truck up...

Wow, what a wealth of information you guys are!! Thanks a lot!! What causes the truck rattle in this situation and my gauge will stay low for at least a minute sometimes longer. I usually have to start driving before it will come back to normal.

Yes, quite normal. Mine runs pretty far low voltage (far left of guage) with the grids running on a cold start... after just a few minutes, the grids stop cycling & the alternator recharges the battery to replace the power drawn out of it starting. Diesels are a different breed.

Thanks to all for the replies and helpful answers. This is a terrific forum with very knowledgeable people!!

For reference the grid heaters operate with pre-heat anytime the intake air temp (intake manifold) is below 66° F. The duration and frequency then varies based on ambient temp (at the sensor just after the air filter). Some post-heat uses both elements and some are just one, it just depends on the conditions. They will run for approx 2 minutes after startup, or until you hit 18 mph. Like Micheal said the grids pull 195 amps, and you have a 136 amp (peak, not at idle) alternator so there is no way to avoid the voltage drop. Contrary to urban legend it does not effect alternator or battery life.