d4 6-U pony engine running how long can i

By all means go after the pony water jacket and clean it as well as possible but when it comes to the main, be a little gentler at least around the base of the sleeves. I washed away too much sludge and created a leak on a D6. I was flushing in the block drain hole and I think the jet of water rushing in cleaned the area around a sleeve or two and the bottom seals began leaking FAST. In the end I was able to use a stopleak product and sealed it back up but it cost me some time and a couple oil changes not to mention a few more grey hairs in my head!

The V4 pony motor on the John Deeres has its own water pump. So it circulates even without the big motor spinning.

The D318 pony has its own water pump also. Running a pony with its own pump for extended periods should not be a problem.

so the pony on the D315 doesn't have its own water pump but the pony on a D318 of the same year does???

Yes that is correct

Thanks. yes i checked my parts book and couldn't find any reference to a water pump. also went to the operators manual for the detailed starting instructions for both engines. there was no mention of the pony overheating but the manual mentioned several times to let the pony warm up until the lubricating oil could properly lubricate the pony before attempting to start the diesel. the manual also states that as soon as the pony was warm to get ti to cranking the diesel under compression until there was enough heat generated through the manifold and compression to start the big engine. the manual stated that several minutes could be normal under normal circumstances. there is also a method similar but has minor difference for cold weather operation.

It doesn't take long to warm the pony enough in order to start cranking the main engine. Depends on ambient temperature but it wouldn't be more than a minute in a lot of cases, less where it's warm. There's cranking the main engine without compression and then there's cranking it with compression. After the pony has warmed, then crank the main without compression until at least the main's oil pressure comes up - that requires less pony power than cranking under compression unless it's super cold, and enables the pony to warm up even more, before you use full pony power to crank under compression. You just need to figure out what's best for the conditions and your tractor, but extended idle warming up is not recommended by engine manufacturers.