Yanmar 2QM20
Dear Joe:Gives me comfort that your original engine is still giving good service. I've also recently done some maintenance: New impellers, changed the fluids, checked lines and hoses, and adjusted the valve clearance. I was pleasantly surprised to see how clean the valve area looked when I had the valve cover off. Not a bit of sludge or sediment anywhere. Maybe some head work was done by a previous owner. I was asking about your engine because although mine is running fine (starts quickly, no smoke, and will attain the rated rpm's), I do have doubts that everything is alright. I have made a booking for the local Yanmar repair shop to come out to assess the engine condition.Congrats at making a successful go at the instrument panel. Mine is looking quite dingy. The previous owner purchased and mounted at the nav station a complete set of guages, but didn't install any new sensors on the engine. I'm leaving this "as is" for a while since the original Yanmar temp/oil alarms seem to be working and I don't yet know how to convert to the new guages but still retain the audible alarms. A project for the future.I am having my engine looked at because:- With time, the coolant begins to turn black. A very fine sediment precipitates out of the liquid when it is undisturbed for a while. Helpful members of this forum have suggested this condition probably indicates a small blow-by of combustion gases through the head gasket into the coolant circuit-- i.e. the gasket will need to be replaced. (Or hope not - a crack in the head could cause the same symptom). - A clicking noise which I am not sure is normal. Maybe an injector.- My SELOC Yanmar Repair manual says that one/two/three cylinder engines can vibrate significantly. Mine does at very low rpm and at another rpm band as well. Same whether in neutral or under power, so I don't think its alignment. This is probably not an issue, but I want a technician's opinion.The engine on my boat "Wildaire" is model 2QM20H (H=raw water cooling) that was converted to a anti-freeze coolant system by adding an impeller pump along the alternator belt for drawing in raw water to an external Densure heat exchanger that is mounted in the port lazerette, then to the mixing elbow for discharge. The engine's original salt water system was converted to now recirculate the coolant through the engine and back through the heat exchanger in a loop. Obviously this system has been working fine for many years, but I have found out that one drawback is that Yanmar only makes a 120-140 degree thermostat that can fit in the 2QM20H housing of the raw water designed engines. Your 2QM20F's thermostat operates in the 160-190 degree range. I have been told that salt water begins to leave deposits in the engine at over about 150 degrees, which explains the low thermostat temp rating for my engine. My engine only gets lukewarm. I have read somewhere that this temp is way below the optimum efficiency for a diesel and that over time faster cylinder wear will occur. regards,rardi