hey guys,
as some of you might know, i have a D4 HT4 crawler loader. in my last post i was unsuccessful at trying to locate a front grill to replace my bent one. so i have a different question this time. i was wondering what oil should be best used in the engine, and the 2 valve hydraulic system. i am currently running these oils.

Engine Oil- SAE Rotella 30 weight/STP mix
hydraulic oil- also using SAE 30 weight.
injector pump- 30 weight
starting pinion- 30 weight
Pony motor- 30 weight
throw out bearing- 90 weight/STP mix.
final drives- 90 weight
transmission- 90 weight

found out that using 30 weight provided good lift and less leaking from the hydraulic cylinders. as for the engine, i figured to use 30 weight since this is basically all they had back in the day. my one close friend and retired mechanic/machinist from the mine, he uses 50 weight in the engine for the extra oil pressure. his D4 is the same as mine. might as well throw in the question of oil pressure. what should be the normal operating oil pressure for the machine? since the old oil gauge only had colors, that couldnt be really trusted so i put a gauge with numbers on there. i rather see numbers than some color that could be wrong half the time.

If you have adequate pressure, I would guess in the 25-30 psi range would be about normal, then heavier oil will not help things. The pressure is regulated in the oil pump by an inlet throttle valve that senses off the pressure available in a main bearing near the pump, so pressure is not going to be any higher that whatever the valve is set for.

The viscosity depends on your weather/operating temperatures. Mostly 30 weight is recommended for above freezing and 10 wt for below. Now you can use the multiweight oils if you find that your conditions vary from one to the other or you have the oil for other equipment.

There's been a discussion on here about using some of the newer oils vs the older spec oils and my impression is you might be safer to stay away from some of the oils required for the newest on-road diesel engines.

I had a barrel of 50 wt Delo that I got cheap(er) from the local Chevron jobber and I used it in the D311 and D318 the last time I changed the oil. Now that they've run some (close to a year, but not too many hours) I'm sure the bulk of what is in them is 15W40 that's been added since.