Bad temp guage or sending unit?

[Cheechako]

My '85 4-108 never overheated, it was pushing a 44 ft boat too. If anything it ran too cold. I think there were at least two heat exchangers on those 4-108's. Mine had the big one mounted on the engine on the port side with the end caps to remove the heat exchanger tubes. The fill cap was not part of the heat exchanger but was front mounted on top.

[CSY Man]

If this is something you cobbled together yourself, that's quite possible. If it's a production boat that didn't overheat from day one, something has happened over the years or all of a sudden that causes it to overheat. Find what it is, correct it, and the froblem is fixed

Yes Sir, will get right on it...

Not so easy. The engine has ran hot if pushed, from the day I bought the boat 14 years ago and same with the previous owner. At normal cruising power (2100 rpm) there is no problem, even at 'high" cruise it stays steady up to about 2600 rpm, anything over that and the temp will slowly build up to the red. Quite a few 4-108s have had the same problem and some have not:

My '85 4-108 never overheated, it was pushing a 44 ft boat too.

Again the question here is them Laser Guns, and where to point them to get an accurate reading? One would think the surface on the outside of the engine, exposed to cooler air, would be cooler than the actual coolant inside the engine and there would be a measurable difference?

[kmaz]

CSY Man, I've found using my infra red gauge on the temp sender is giving me what I need. Additionally, the coolant reservoir for the water heater is in the port lazarette and reads within a few degrees of the temp sender so I can check from the cockpit until my new temp sender somes in.