OK, so I've had a mysterious battery drain going on for a while. In the summer, if my truck sat for 2 or 3 days the batteries would be dead and I would have to charge them or get a jump. Now that it's cold, they will be dead in about 8 hours. I go in to work come out 8 hours later and no start. Sounds like a battery problem. Well, a load test shows the batteries are good. I have put on a new alternator (old one was bad) and starter. Using a multimeter, I have pulled fuses and tested for a current draw. Only draw was radio. It was drawing .02 amps, not enough to kill it that fast I would think. The GPR tests good. I tested glowplugs and #8 is bad. Last night I charged batteries with the cables off. This morning they show 12.5 volts each. So, I hook them up and truck wouldn't start. Hmmm, can't be the batteries. Right? It just doesn't have the power to crank over on it's own. When I jump start using another diesel or 2 cars, it gets plenty of power and fires right up. Has anyone had a similar problem or any ideas what to look for. I have been reading other posts and have ran out of ideas. Sorry for long post, but I wanted to get all the details in here. Thanks

 

Have you had the batts load tested? What kind of voltage do you see while cranking? How old are the batts?

 

Might put a volt meter on the batteries while trying to crank and see how low the voltage goes, if it drops below 10.5 volts I don't think it will fire.

Also, might check the ground cables where they terminate on the frame and clean.

Tom

 

With a fresh charge on the batteries and no fire this AM without jumping it, I'd be tempted to think they are the culprit. How old are the batteries? Even if they load tested okay, they might still be suspect. I'd start by cleaning the terminals and cable ends up real good and see if it helps any. If you could swap batts with another rig temporarily just to eliminate yours as a potential problem that might help too.

 

I went out at lunch to check volts while starting. 12v prior to start, dropped to 10.5v while wait to start light was on, then dropped to 6.5v while trying to crank. It didn't even try to start. Even though they test good, just must not be putting out the power to start. I guess I'll have to get another pair of batts to swap out and check it. The batts in it are 1.5 yrs old.

 

6.5v definitely is not enough to crank it over, they need around 9 or 9.5. Sounds like your GPR is pulling quite a bit, you might want to replace it (should only pull around 1v).

 

If it starts with a jump that eliminates everything but the batts or the negative batt connections if you used a frame ground or engine ground for the negative jumper cable. If the voltage drops to 6.5v then the batts did not pass a real load test.

 

Yeah, the shop guy said "their good" after using the BS hot coil type tester that takes about 5 seconds.
I was like "really that's it for the test".

 

I just had a battery load test ok a month ago but of my two batts it would keep kicking off the charger. Although it did finally charge ok it didn't pass the real load test the next morning. Also keep in mind that one bad battery has a real negative effect on the other battery. It can discharge it while the truck just sits or keep it from charging properly while truck is running.

 

Another thought is to feel the alt in the am or after it has been sitting for the 8 hours that you are at work. If the alt feels slightly warmer than the ambient air temp then the diode in it is gone and that is draining your batteries.

 

That's a good idea but it done the same with the batteries disconnected
Just about leaves 1 or more bad batteries

 

I would say that is a definitive test in itself! Bad batteries.