Coolant Gauge Wildly Fluctuating.

The coolant gauge is fluctuating wildly on my 98 fifth gen. When the bike gets up to temp, 170f to 190f, the readout will start to fluctuate showing temps anywhere from 180f to 240f. I suspect that I may have a stuck thermostat but I was wondering if anyone has experienced this issue and what was the solution? 

bump

A little more detail perhaps will help.  Does the temp  fluctuate quickly up and down showing 170f to 190f and back?  Does it do this while at steady state cruise, stop and go traffic or inconsistently?  Is your fan turning on?  If the temp is fluctuating all over the place without reason, I would be more suspicious of a coolant temperature sensor rather than the thermostat.  If the fan is not working, temp will jump up in a hurry in stop and go traffic.  Have you changed coolant recently and perhaps didn't get all the air out of the system?  

Mine goes upto 226F (108C) but then it goes down as the fan kicks in.

According to my son (bike mechanic) the coolant may go up to 239F (115C) without problems, however it should not pass that mark to be safe.

Are you sure you see 240F? As is you see that you have air / fan / thermostat problems.

Do the fans start at about 226?

As said, mine goes up to 226 and then the fans kick in and it drops to lower values, however I have seen this on very hot days of 95F (35C).

240F should not be a problem if the outside temps are 95F or more as long as your fans kick in en bring it down.

The gauge will read 195 then 184 then 224 all in a matter of seconds. I owned the bike since new and this is not normal. I have only about 30k miles on the bike, but it is 16 yrs old so some new parts may be needed. 

Do you hear the fans? Also, what is the outside temp when you notice this?

195F is rather cold and 224F isn't abnormal either.

Looks to me your are worried because water boils at 212F, but the coolant isn't water, it boils way higher and such temps don't hurt your bike one bit.

The first time I saw it, I was worried a lot too, but my son (bike mechanic) told me it's normal, So I stopped worrying.

Yes it's seconds, when the fans start....you should be worried if it keeps rising over 230 and doesn't come down.

If the temp is fluctuating all over the place without reason, I would be more suspicious of a coolant temperature sensor rather than the thermostat.

+1

Honda OEM Part: SWITCH ASSEMBLY, THERMOSTAT #37760-MT2-003

It's on the bottom portion of the left side radiator.

http://www.vfrdiscus...ensor-location/