Yanmar crawler

[gus]

Well, sort of. I have a Yanmar excavator, 6000lb size, mid 90's production. I hope someone is familiar with these things as I have had it about 6 mos and have a couple of questions. The guy I got it from, part time dealer, didn't have a clue.

There is a small valve in the cooling system with a line to the back of the head. How much should it be open?? If it wasn't needed as valve it would be wide open, so I guess it needs to be adjusted. Or, should it be closed and used only as a drain??

There is a warning light, amber, that comes on when starting up and stays on until it's at operating temp then goes off or sometimes comes back on and off, this does vary. Even when at operating temp. It comes on when the engine is shut down and the key is still on. As does the oil light.

There is a temp guage but no oil press guage (red light only). Also a green third light that I have no clue what it's for as it is also unmarked. Only the oil light is marked.

[Ray III]

Line goes from back of head to where?

[gus]

There is a needle valve just ahead of the thermostat (pressure side) with a line (1/4" approx) to the back of the head.  I have no idea what it is for or how much the valve should be open.  gus

[Ray III]

The general plan of water cooled engines is that the water pump pushes coolant from the front of the engine through the block, cooling the cylinders, then the water goes up through holes in the top of the block at the rear, and comes to the front again through the cylinder head, exiting at the thermostat housing.

So it sounds like the line is to allow some coolant to bypass the cylinder head. I'm not sure why, other than a possible increase in combustion efficiency. Is it a diesel?

[gus]

Yes, it is a 2 cyl diesel. I'm still trying to figure out why they put a valve on it. How would you know how much to adjust it?

[Ray III]

I wouldn't, never saw such a thing.

If it has good power and doesn't smoke then I wouldn't fool with it.