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@cookies you should not run an air cooled engine below max rpm, they do not cool properly, same thing with most engines in ag and industrial applications, the entire thing is made to run at full throttle. I have seen many engines either cooked ( air cooled) or the cylinders so glazed over they are junk (liquid cooled diesel) running too cool, there is a reason that things are governed at a specific RPM!
I'd beg to differ with that.. Although you're right, that the engine speed impacts the cooling of the block of the engine, on most splitters, the engine is under virtually no load when the ram is being reversed, or not moving at all. So, while the ram is doing nothing as you stack wood, move wood, get another piece of wood to split, etc., there's no additional heat load to the unit. When I'm splitting by myself, I doubt if the engine is under load more than 20% of the time. When I am splitting, ( 27 ton splitter), unless it's a really big piece of wood, the engine note seldom changes, indicating that there's very little load on the engine. It just pushes the ram through like there's nothing there. When the ram first contacts the wood, that's where the most load on the engine / pump occurs. Usually, once the wood has cracked, the ram just floats through as it separates the two sides of the split.
I agree with you that an engine under constant load needs full throttle for cooling ( think mower with hydro-static drive, in wet grass, etc.), also especially if it's a 2 stroke application ( Line trimmer, chain saw, etc.), stuff like that can experience a 100% load for a significant amount of time .
But from my experience, a splitter just doesn't have enough of a load on a regular duty cycle, to have to worry about running flat out for cooling purposes. The engine fan seems to only cool the engine, not the hydraulics, although there is a bit of bypass air flow that goes past the hydraulic pump, but if that really needed cooling, there'd be fins on it. . Also, in cooler ( colder) weather, there's way more heat transfer from the engine's fins, due to ambient temperature transfer..
Then again, maybe you, and with some help while splitting, might have a higher loaded duty cycle, than my old retired butt, splitting by myself. In that case you might be right about full throttle operation for proper cooling. Especially on a hot Summer day.
As I posted earlier, I don't usually run wide open, nor do I run anywhere near idle. My splitter has a "happy zone", where it's inherent harmonic vibrations (from the engine) don't make it seem to want to shake itself to death.
Hmmmm.. Liquid cooled diesel, running too cold.. That's a thought for another day, and another thread.. Interesting.