Low tech temp sensor...How hot should it be?

[Dale I]

Put your right hand in and move it all about.... When I'm firing off the little Yanmar and wondering if the waters flowing, (can't really see the exhaust exit under the stern), I generally keep one hand on the mixing elbow and the other on the water jacket. I generally find that the elbow is always luke-cool and when things finally warm up I can usually do a 10-second count with my hand firmly on the warmest part of the exhaust water jacket before it becomes too uncomfortable to touch... (the elbow is always just 'warm') Does that sound about right to those of you with _real_ gages? I have raw water cooling. Is it true that with raw water cooling that if the thermostat maintains the proper operating temp for a diesel engine that the salt water will become more corrosive or clogging to the cooling jacket? If you maintain a lower temp for that reason won't the diesel will experience a build up of carbon....? Which is the lesser evil?

 

[Bob]

Thermostat @ 140

Hi Dale,My raw water cooled Yanmar uses 140 thermostat. I can check exhaust for water flow. Engine equipped with O/T alarm. Have 22 years with same boat and engine. Never overheated to trip alarm. Saw more vapor once while cruising - found inlet was plugged with mussels - cleared same while underway.Replace thermostat at 15 years along with exhaust elbow / mixer. Exhaust was severly restricted. Block was / is in great shape. Boat is moored - engine hours typically 50 - 100 per year for cruising - daily use typically 0 - sail from and to.Would not use higher temp thermostat to improve operation on a raw water cooled engine.

 

[Dale I]

Thanks Bob.

I appreciate your feedback. In regards to the raw water inlet plugging, the previous owner had what I thought was a practical solution. He had tee'd the raw water intake off to the side above the thru-hull which enabled me to remove a plug and 'rod out' some leaves straight through to the outside and flush the intake without ever diving the bottom....

 

[J. Tesoriero]

Raw water diesels run cool.

Small diesel engines with raw water cooling are designed to run cool. On my 15 HP Yanmar, the thermostat opens at about 125 degrees and the temperature alarm goes off just above 140 degrees. If you are concerned about carbon fouling, run the engine under load for an hour or two at full throttle once and a while to clear its throat.