I've been unable to pin down the EXACT reason for my overheating/coolant loss problem, so I'm incorporating almost all the suggestions made so far.
First, I've replaced both hoses leading to and from the hot water heater. (All the other engine
hoses are visible and appear to be in good shape.)
I've replaced the coolant "over temperature" sending unit. For reference my 4-108 and maybe others have two temperature sending units; One is of the variable output type and leads to the temperature gauge. The other is a normally open switch that simply closes when coolant temperature exceeds 277 degrees (!). This switch was apparently not operating or not correctly wired. I've replaced it with a new one and, using new 12 gage wire and fittings, wired it into my "loss-of-oil-pressure" alarm
circuit: a nice LOUD bell.
Per Maddogs suggestion, I've installed an elbow
that will enable me to top up the coolant at the new water temperature sensor on the highest point in the cooling
Per Chucks suggestion, I've installed an expansion tank with a lead to the overflow tube just under the cap on the heat exchanger
. If this works as advertised I should be able to monitor
coolant level more easily because it will be more visible. (I can understand how coolant can be pushed out of the engine here, but I'm mystified how it can be drawn back in considering the 7 pound pressure cap ... but so be it.)
Well, if everything works my overheating/coolant loss problem is solved
. At least, if she does overheat the new over temperature switch should give me time to shut down the engine before she seizes.
We're soon to depart mid-Florida toward New England
. We'll be sailing outside and motoring in the ICW
depending on weather
. About 1500 miles North and then 1500 miles back in the Fall. The voyage is sure to include lots of motoring. Wish us luck, and thanks for all your suggestions.