i am very new to diesel. I have a 98 24 valve. yesterday it started having weak startups and this am it wouldn't start. battery terminals were a little corroded, so i cleaned them up and still nothing.batteries were good so i replaced starter. 1st start perfect but when i turned it off it stopped instantly which is not normal,almost like it was seized ( it usually sputter's for a second). 2nd time it could barely crank, not like a dead battery but It seemed like it was under a lot of pressure, it would try to turn but couldn't. 3rd attempt i got nothing.both batteries still tested 12.1 volts so i left it to call a mechanic friend and when he called me back about 1 hour later i went outside to tell him what was going on it started up no problem. again i tell you i haven't a clue about diesels, i can do most anything with a gas motor but completely lost on this. it has been couple hours and it seems to be normal.Any Ideas?!?!?

 

https://www.dieselbombers.com/24-val...-when-hot.html

 

I would still have your batteries tested. take them to a auto place-advance, auto zone, oriellys... have them load tested. 12.1 seems a tick low for the batteries.. they should be 12.8+