My 2006 Dodge Ram has been slow to start on cold mornings (below 40F) recently. The truck acts like it does not want to turn over first thing in the morning, and the battery guage reads about 8v. After startup, I can turn it off and it will usually crank right up. Additionally, if I plug in the block heater it seems to have no problem cranking in the morning. Had the batteries tested (both replaced almost 3 years ago) and they were checking good and in limits after having driven my truck to the shop. So at first I thought the batteries had gone bad, because my satellite radio will default to channel 184 when I turn on the truck, but now I am worried it might actually be one or more injectors although I have noticed no secondary signs of a bad one. For reference, I have owned it since Jan 2006 (new) and there is 135K miles on it. Any thoughts would be greatly appreciated. For now I will just keep using the engine block heater.

 

This kinda sounds similar to the folks with the complaint their truck won't start unless it was plugged in overnight. IIRC, most if not all of them pointed to bad injectors. I would look at having them tested and either rebuilt or put new ones in. I had mine in the '03 tested and rebuilt years ago by F1. No complaints.

 

40* F is nothing, and your truck should easily crank over. When you get down around 0* then we're talking colder cranking temperatures. Has the starter ever been replaced with a parts store "lifetime warranty" unit? Hopefully not because they're no where near as good as the OEM starters and tend to drag due to early wear.

I dont know who or how they tested the batteries either but dual battery systems must be tested with the batteries fully disconnected from the truck and each other. The neg and pos can not be connected at all otherwise they give false readings as they mask one another. Load testing is always best but you can also test the batteries with a simple test voltage tool which will tell you a lot. Simply disconnect the batteries and test their static voltage as they are in the morning when you're normally having cranking trouble. If they read 12.4 volts then they're going bad. Anything less and they're toast. A good battery will be around 12.6/12.5. A tip top perfectly charged battery will be 12.7 but 12.6 is more likely what you'd see.

Also, corrosion build up is a problem for people who live where road salts are common in the winter. Loose or corroded grounds or corrosion inside cables will cause loss of amperage during load conditions.

 

I replaced a slow cranking starter with a new one , problem solved this happened to me on 2 trucks I own. asa it got cold oil thick, it would slow crank even with new batts.