What will make the Viff run cooler?

Alright. I finally got around to testing the old thermostat.

It opened around 185 and was fully open around 205, according to the precise and professional meat thermometer I bought at Cub Foods. Accounting for instrument imprecision and operator error, the range is probably within spec. I'm not sure that the opening is, though. The manual specifies 8mm minimum.

Here's the best picture I could take of the maximum opening, as the water was starting to boil at around 208 deg F.




I'm not sure where the measurement should be taken from--what are your thoughts?

 

Looks to me as if it was not opening all of the way. 8mm is somewhere between 5/16" and 3/8". Rough guestimate from your pictures would be that its about 1/8" of an inch from being fully open... which translates into it opening only 2/3 of the way. The VFR runs hot enough the way it is when the thermostat is opening fully so this could explain the hot temps. Only a test run will verify. You might be able to do it by letting it idle. It shouldn't get any hotter than 1-2 degrees above what the fan temperature switch is set to turn the fans on. I don't know about the 5th gen but on the 6th it is 223F. I can let mine idle all day long and as soon as it hits 223F the fan kicks on till it gets down to around either 212F or 210F. Doesn't matter if it is 95F or 15F out.

 

I know that most are more mechanically inclined than me on here, but 3 quick questions: You mentioned you changed "most of" the coolant. What was the reason for not changing "all" off the coolant? Was it "nasty" looking? What type of coolant did you replace it with?

I always try to do the simplest thing first. Handles funny? Check the air pressure before I mess with the suspension. Runs hot? Check the coolant before I change a thermostat (especially since coolant is a lot easier on these bikes than a T-stat).

I hope it all works out for you. Good luck!