On a slightly different tack from each of the foregoing comments, I've been reading through the manual for the MD 2020 engine on my B36(2002), and noted the following instructions, first under the following heading:-
Heat Exchanger. Cleaning
"Cooling performance is reduced by scaling in the heat exchanger. It should therefore be flushed when the coolant is exchanged.
Under
Coolant. Changing,
the manual stated
"The corrosion-proofing additives become less effective with time and the coolant must be changed. If the freshwater system is filled with antifreeze mixture it must be changed every other year (two years). If the system is filled with anti-corrosion agent mixture it must be changed every year.
This year shortly before bringing the boat ashore for the winter I looked more closely at the fresh water expansion tank which is located in the upper area on the aft bulkhead of the engine compartment near to the port side and where it is not at all easy to have a good close look at it without more contortions than my body was designed for. In the end I took off the black plastic filler cap on that tank, and stuck my fingers into what I thought would be water, but which turned out to be a mass of brown crud which fortunately is not connected to the toilet waste system !! How anything actually flowed through that expansion tank is a mystery, but it got me thinking that I'd not changed the cooling water ever, and I'm guessing the previous owner didn't, so it was likely that the cooling waterways might also be partially blocked with similar crud.
I couldn't see the liquid level in the expansion tank, so took it off last weekend and brought it home where I've managed to clean and remove at least 99% of the crud using initially some thin bleach left on an overnight soaking (not very successful) and then some Lime Scale Dissolver from the first mates cupboard full of useful liquid cleaning products. It worked like a dream and I can now see the liquid level within that tank. The coolant drain valve on the starboard side of the engine is just a screwed in plug on mine, so that will be released next time onboard and the system flushed through with water.
So the question is, if your engine is getting warmer than you think it should, have you changed the coolant at the recommended frequency of every one or two years depending on exactly what it is that you have in your fresh water system
?
Oh well, it's nice to know I'm not the only one who didn't think about it !!