Just the last couple of weeks I've had to keep this truck's block heater plugged in for a longer period of time to get it to start. Last year it would start in the same cold temps, but this year it is acting like an older truck. One morning with about -10 degrees and only an hour of block heater it only turned over a couple of times and then clicked like it had dead batteries. I started it later that day with a battery boost and leaving it plugged in about 6 hours. I had NAPA put a battery tester on it and both tested ok with good voltage. I got around 13 on both batteries for voltage after it had started and run a while, I didn't test it before it was started. If I leave it plugged in 3-4 hours early morning it will start but still turns over hard (turns over slow). Temps have hovered around -5. I had the FICM replaced last fall so this is starting to feel like aging batteries on their last legs but I thought I'd see if anybody had any other thoughts or similar experience? The truck is a 2005 bought in Oct. 2005. It still has 15-40 oil in from last fall since I don't put much mileage on it. I have not added any diesel additive at this point.

 

Detail how NAPA tested the batteries?

What is max voltage you are getting after 20 min running and idle at 2,000 rpm?

What is voltage sitting still in the morning?

What is voltage at cranking (with glow plugs on)?

 

Thanks for your help.

 

Batteries lose capacity as they get older. Batteries also lose capacity as it gets colder. At -10F you may be down 75% of warm weather capacity. Old and cold is a double whammy.

Your batteries might test OK at quick parts store test, but still not have enough power to crank your engine on a very cold morning.

 

regardless of the cold, you should have 12.8v. You have to disconnect the positive batt cable to test each batt independently. You may only have one bad batt.

 

If the NAPA guy did not disconnect the two batteries and load test them separately, they did not do it right.


Do the voltage test with a helper at the coldest point in the morning before the engine is run --- If you are below 10V with glow plugs on and everything cranking... let me know.

Right now, I suspect batteries, but not alternator...

 

Voltage while cranking was 9.93.

I didn't think about the batteries being wired together while they were being tested at NAPA. I need to disconnect and retest to narrow this down to each battery.

Thanks for your help.