Modern Vespa

Hello all. I recently did a coolant flush on my 04 GT200. Since then when I start it up, the temp gauge gets to high, whether idle or I'm riding it, and then drops to a more normal level after 5-10 minutes. As the temp rises, the idle starts getting rough and can stall out. I've tried manually bleeding it by disconnecting the hose coming from the carb to the thermostat housing - but just liquid came out, no air. Any thing else I can try?

thanks in advance!

Check the thermostat first. If it is good then most probably your radiators are fouled.

How did the coolant that came out look? I'm wondering if there was crud that might be clogging things up and need further flushing.

How much have you ridden since flushing? I believe the GT200 is "self bleeding", so it benefits from a bit of bouncing around to work any air pockets to through.

It didn't look great. I thought I poured enough distilled water through and it looked clear. I rode a few times, but seeing the temp gauge rise to high freaked me out and I kept the trips short.

Honestly wouldn't be surprised if there is still some gunk. I keep finding that this was not a well cared for machine the more I work on it.

Maybe a good bet is do a system flush/clean with one of the different products to clean radiators and only after that put new coolant and test?

Have a read through this, and flush it with simple green. Then run a couple of cycles of straight distilled water through it before refilling and burping: NVR- Need Recommendations for Safe Radiator Flushes… (Post 2704721)

Thank you, I will take a look tonight. My goal is to make the group ride on the 14th!

A 50/50 vinegar and water solution is an excellent way to get out the scale and other crap that gets in cooling systems over time. Leave it in for about half an hour, then let the engine cool before you drain and flush the system a couple of time. You can remove the thermostat housing and back flush with a garden hose, which can be interesting, depending on what comes out the other end. Flush with distilled water, then put in a 60/40 blend of distilled water and coolant. That ratio performs very well in small engines, and won't cause further corrosion.

Did the Simple Green HD flush, distilled water flush, flushed through the thermostat opening, and it wasn't as bad as I thought it would be gunk wise. Actually ended up being pretty clean. Had the same behavior after all the cleaning - high temp and then rough idle. Ordered a new thermostat, will give that a shot tomorrow. Thanks all for the tips.

Thermostat replacement did the trick. Hasn't gone past medium on the gauge. Idle is much better. While I was replacing the thermostat I went ahead and tore the carb apart again. Replaced the float bowl gasket, main jet, another thorough cleaning and I'm liking how it is so far.

Thanks all for the tips!

I recommend Maxima Coolanol ready to use coolant, and so does Robot at Scooterwest. It's what I use in my GT200. It's both a good coolant and water pump lubricant.