I had forgotten that more gauges was a major theme in this Yanmar forum back when I first started reading here. In fact I bought a gauge but never got around to installing it. Don't remember if it was Temp (likely) or Oil Pressure. At any rate I eventually gave the gauge away.
I am now of the opinion that Yanmar got it right with all of their design choices on these old classics. It's worthwhile to verify that the dash lights function properly. But that's all the attention needed. Just do a thoughtful warmup before running the engine hard.
The temp light seems to have been designed as simply a boilover warning, with different spec senders between the thermosiphon and pumped cooling systems. And anything short of boilover considered an acceptable operating temperature. Diesels are more efficient at higher temperatures. There's not even a thermostat in YM2000. They didn't overlook it, they designed a system where the warning light is all that is needed. Simplicity as a feature, as proud evidence of careful design, not simplicity as a cost savings.
It's obviously important to keep the cooling system up to spec, with the proper coolant and radiator cap, and the radiator rodded out or replaced if it doesn't cool properly. Yanmar expected thoughtful maintenance.
Some of these engines ran a lifetime of high output in semitrailer refrigeration units where nobody climbs up there between suggested maintenance intervals. Small offshore fishing boats, similar, where the owner literally owes his life to diesel engine reliability.
Now 40 +years later the fact that most of these tractors we own have only needed appearance reconditioning suggests that Yanmar got everything right, so long ago.
