I don't know if this would make any difference to you (in terms of sourcing parts) but I thought the Yamaha F80/F100 was only made through 2002. Then in 2003 it became the F75/F90 (I'd guess it was something about horsepower measurement rules rather than change in the engine), and then I believe in 2005 the engine was changed to fuel injection (which of course was a real change).
So if you have an F80 it seems as though it may be a 2002 (?). Now maybe the thermostat for a 2003 F75 and a 2002 F80 would be the same anyway, but I just thought that in case your engine is a 2002 F80 you might like to know that for purposes of discussion, parts ordering, etc.
A quick way to tell is to look at the last character of the model number. If it's an "A" then it is a 2002. A 2003 would have a "B" as the last digit. So my 2002 F80 is model TLRA, which means power trim tilt/long shaft/remote control/2002.
Here is a "decoder" for Yamaha which covers the years 1991-2005. Sorry about the poor image quality.
While we're on the topic, you might be interested to know when your boat was made. Maybe it's an early 2003, which would easily explain a 2002 engine. If you look at the boat's HIN (on the transom, starboard side near top), the last four digits will tell you two things: The first two of the set will tell you the month and year the hull was laid. The letter is the month (A=January, B=February, etc.) and the number is the year. Then the last two are the model year of the boat. So for example if your HIN ended in J203 then your boat's hull would have been laid in October of 2002 and would be a 2003 model year. Oftentimes the years match, but it's not uncommon to have a split like in the example for a boat started late in one year but completed in the subsequent year.
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