Les
If there has been an changed in how fast your bike cools down this summer vs. previous summers at the same air temperature and same ride, perhaps your thermostat is getting sluggish. I'm thinking of the coolant thermostat in the engine, not the thermoswitch for the fan.
And check there is no change to the air flow through the radiator core. Obstructed with a new rad guard or just full of mud or road dirt. Flies and the odd bit of grit are a fact of life and accounted for with extra capacity at design.
Make similar checks for the oil coolers air flow as this ships plenty of heat from the engine once road speeds pick up and removes it from the most important areas of oil and sump after a long idle or slow crawl. Oil cooler hardly does anything at slow speeds and even tends to warm the oil up at idle on a hot day because it's right behind a very hot exhaust pipe. It's the all too invisible oil temperature we should be just as concerned about. This can be at the opposite ends of maximum and minimum values to your indicated water temperatures. Only a low percentage of engine oil flow passes through the cooler at idle. The rest by-passes it straight to the filter and back into the hot sump. I never liked the idea of hot oil and tried an additional electric fan on the oil cooler but found low oil volume through the cooler at idle and just above meant it was a waste and hardly effective. In fact the extra electrical load of the fan probably made the engine slightly hotter.
If you take the thermostat out to test and inspect it should start to open at 190 degrees F or 88 degrees C. Hang it on a bit of string in a light coloured pan of water on the stove. You need a thermometer to spot as it passes opening temp. Boiling point is easy to spot. Use a long string. Keep it away from the edge of the pan. DON'T SCALD YOURSELF. Light pan lets you see through the valve better to spot when it opens.
At the boilng point of water (not antifreeze mix) 212 degrees F or 100 degrees C it should be open by at least 0.31 inch or 8.0mm.
If it's not open as specified here it definately needs replacing.
I can't remember what year but some earlier bikes had problems with the water pump impeller vanes cracking off. Made of plastic and moulded to the end of a steel shaft. Pumping efficiency is crucial at low engine speeds so could be the start of this. Easy to lift the cover on the pump if you are draining the water to inspect the thermostat.
I had two of the first water cooled Honda's in the late 70's. Over the previous air cooled engines the oil change intervals went from 3.6k miles to 7.2k miles. Oil capacity went down from a UK gallon to just over half a gallon. Fact we still need to change the oil at 4k miles on these V twins tells me the oil can be expected to regularly get up to frying temperatures (and regular generator problems for city dwellers). The underside of the piston crowns is oil cooled on these engines and you don't get oil much hotter than that if you want it to last for long.
If I ran one in a city through the central American summer I would drop to an 8 or 10 degrees C lower temperature water thermostat. That bit of extra cooling capacity left to absorb the heat soak at low speeds and idle could improve the bike no end. A radiator fan that cut in 10 degrees earlier would be harder to do but also help. Keeping the revs at 2k rpm and just above rather than down at idle speeds will also improve water circulation (engine driven fan on the old Honda's so was even better). And of course if a traffic jam dictates you can turn the engine off with the kill switch before it heats up then all the better.
SVman
