safe temp for a Perkins 4108 50hp?????

[Guillermo]

I absolutely agree with Fast Fred. Oldies go cooler.
My boat mounts a Perkins 4236M from 1971 and it has been running smoothly for all this years at around 170 ºF (+/- 77ºC).
212ºF (100ºC) is the boiling temperature of fresh water at sea level, so you need a highly presurized cooling circuit for this. Older Perkins (4000 series) cooling circuits were not conceived for high pressure, as far as I know.
Around 175ºF (80ºC) is a most usual temperature for these kind of engines.

[David P]

We just went through a long process trying to figure out why our Perkins 4-108 engine was running hotter than it used to, and we finally figured it out! There is an L-shaped pipe that is the raw water return from the heat exchanger that mixes the raw water with the exhaust at the exhaust elbow. There is a flattened spray nozzle of sorts in the pipe that was almost completely blocked by small bits of the pencil zinc that goes in the heat exchanger. One of the symptoms was that there was more exhaust smoke than you would normally see coming out of the exhaust pipe. This smoky exhaust occurred at all RPMs. The temperature increased with RPMS, going up steadily to about 195 degrees at 3200 RPMs, then slowly rising after that. We could stop the rise by slowing down about 2500 RPMs. We discovered this after cleaning the heat exchanger, replacing the impeller and replacing the antifreeze. We were getting ready to change the thermostat...