This will likely apply to all scoots, not this mine. Does the engine temp gauge actually measure only the engine or the coolant? I ask because of the times the temp nearly maxed out. I rode a good long ride and only got the temp to halfway after about 30 minutes. It also suddenly dropped again to about 1/3rd just as I was getting home.
For all I know, these are just perfectly natural quirks of this scoot, but I guess it don't hurt too badly to ask.
I will bet SERIOUS MONEY on a funky thermostat,,,,or something is floating around in there and briefly partially blocking flow then getting dislodged and going somewhere else,,,or on the rare occasion not having enough coolant in it and the mill gets a steam bubble inside the engine will not let the coolant pass,,,,very rare and i doubt it's happening here,,,,,my dough still rides on a intermittantly bad thermostat,,,or check the thermostat cover or housing is there a burr or casting irregularity thats restricting the thermostats movement for opening,,,or where the actual valve sits? is it flat and straight or does it have a casting problem or debris under where it sits and your warping the thermostat "frame" when you tighten down the cover so it doesn't go thru it's cycle smoothly???,,,,,,,,and most are measuring the coolant,,,,or oil if "aircooled",,,
Yeah, I agree with John...and Pedro too....they're both valid considerations. What you read on the gauge is the coolant temp at the sensor. However, that's a good indicator of what's happening. If the temp is scaling way up and down something is wrong like the guys described.
Do you have a 2008 hd200?....if so i found an interesting thread on another forum where the owner had the same symptoms you have,,,turns out Sym used some kind of funky coolant that clogs up radiators,,,the guy pulled the rad and plugged the bottom hose bib and soaked it with oxalic acid and hot water to flush it,,,he stated the brown gummy crud that came out ,,,seems OAT or HOAT coolants gel over time and can create problems,,,
I read the whole thread and his symptoms were exactly yours,,, and it turned out about half of the radiator was plugged with this gel in a few core tubes and compromised the cooling ability of the rad,,,,,,end of story
If you don't want to pony up for a SYM radiator you can take the old one off and go to a big auto parts dealer. They'll match one up that's close and it will be a boatload cheaper. Zip tie it in and hook up the hoses, it'll work.
It's one solution, getting the old one flushed is another. I'm psycho so I'd be trying to find a bigger radiator that I could fit into the available space. I found a radiator for $20.00 at Auto Weinie for a bike and it was bigger. I cobbled it in and the bike ran cooler. It's just a thought.