I have roughly a 1986 580D backhoe. Have had for 15 years with relatively few problems. Its Cold where I live and few months ago parked and ran fine. Went to start few weeks later and wouldn't turn over even with charger which always works for starting. Feels like mechanical drag when turning over. Only will slightly move with 200 amp charger. Drawing enough current to trip charger internal breaker. Have gone straight to starter with charger and all cables removed. same Have replaced with new starter and same issue, same moved all levers to relieve hydraulic pressure. same removed all 4 injectors and exact same drag tried different batteries and chargers same voltage tested almost 13v I'm down to pulling hydraulic pump because out of ideas. Fluids always proper level. Basically turned running machine off in 0 deg weather for a week and now nothing will turn over properly injectors looked fine with no rust just carbon. I need help and getting pretty far into what I know. Not a mechanic
Can you rotate the engine by hand? Sounds like you are hydraulically locked ( meaning fluid on the pistons) or the motor may be locked up. Good luck to you.
I pulled injectors assuming if water or such would come out but nothing did. Originally able to turn just a hair by hand but seems to be getting worse. Should I try Marvel oil or other. Not sure if helpful but don't know how much or what to put in there just in case may be problem
Think worthwhile to pull hydraulic pump and see what happens
Check the coolant level. Loosen the oil pan drain plug a few turns and look for coolant to dribble out.
Check your hydraulic couplers at your backhoe valve make sure they are connected and are good.
To start with you have to get it to turn over by hand. It should turn relatively easily with the injectors removed, just by grabbing the fan belt and fan and tugging. If the belt slips on the crank, then you know the crank is tight somewhere else, a frozen alternator will stop the engine from turning all by itself, so the belt is as good a place to start as anywhere. Tinkerer and Coy's suggestions are good. A squirt of penetrating oil won't hurt anything with the injectors removed.
Any foot pedals that control swing or extendaoe? Possibly stuck? Any auxiliary hydraulics fitted using electrics that maybe engaged?