Sunl SL250-22 Cooling Issue
 

So I bought this 2008 SL250-22 from a retired guy that only put 55 miles on it in the last 5 years. I drove it home and it blew the head gasket. Little did I know the PDI was never done and it still had that crappy stuff in the coolant. Took it to a local shop and they replaced the head gasket and got it running again. When I got it home I drained all the coolant and flushed it with hot water for about 30 minutes. Re-filled it with coolant, burping it over and over, leaning it to one side, then to the other, ride for 2 miles, refill, let it cool down, refill, etc..

My commute to work is about 4 miles and the scoot does great. Temp gets to a little less than half the dial and stays there. My commute to school is about 15 miles and the scoot does not so good. The temp rises above the 1/2 mark and then races to the extreme hot mark. At that point it doesn't matter if I idle it down or if I cruise at 20 or 30 or 40 or 50, etc. The temp stays hot.

Anyone else have a similar issue? This weekend I am going to take her apart and pull the radiator and make sure she is clean inside and out, pull the thermostat and make sure there isn't plastic or debris stuck, etc.

Can I remove the thermostat all together? I live in California, don't really have any cold weather. Will removing the thermostat all together cause the coolant to rush through the radiator too fast without having a chance to exchange the heat? I am not too worried about reaching optimal operating temp, but I am wayyyyy more worried about it getting too hot.

Any advice helps. Thanks in advance!!!

I wouldn't be in a hurry to do that. These type of bikes typically have three temperature sensors. One is the thermostat, two is the temperature sensor for the gauge, and three is the thermostatically controlled switch for the fan.

Any of them can go bad. My car has a temperature gauge and last year it indicated that the engine temperature was heading towards red (labelled 260 degrees) but I notice that the fan which was supposed to come on at aroung 210 degrees had not come on.

It turned out the temperature gauge sensor was bad. The engine was nowhere near has hot as it indicated. I used an infrared thermometer on the radiator to confirm it.

Of course the fan thermostatic switch could have been bad but that is easy to test by taking it out and putting in boiling water to see if it operates. Same with the thermostat. Usually the gauge sensor can be tested that way too if you know what the specification is. The specifications is usually so many ohms resistance at a given temperature.

Well the thermostatically controlled fan works, as it turns on when the scoot warms up, and it continues to run as the temp climbs all the way to hot. I'm not so inclined to believe that the temp sensor is bad, I am more inclined to believe that the engine is indeed not getting enough coolant flow to keep cool. But I value your opinion. As an added note when the head gasket blew the oil mixed with the coolant and was a pretty disgusting sludge like consistency. I know that the inside of the coolant system was covered in sludge.

That's a shame. On my bike the coolant goes all over the place even the carburetor. I dread to think how I would get sludge out of all those places. It would not be just the engine but every rubber hose attached to it that contains coolant. Beware using any cleaner with silicates. My bike has a water pump with a mechanical seal that is damaged by silicates.

First I would make sure there isn't any air in the system, even the slightest bubble wreaks havoc. Then you might might try a coolant additive like Water Wetterer or some name like that. I have to assume that your SunL is a Roketa Bali type. The radiators on those is behind the fuel tank. If it's hot where you are it could be an air flow issue and an additive may help.

Hi
What brand are you using for engine coolant?
Once you get the problem solved use only a high quality product
I use engine ice in my Aprillia and have had spectacular results
http://www.engineice.com/index.php
Take care and ride safely
Yours Hank

***UPDATE***

So I tore her apart and when I took the thermostat housing off the engine I could clearly see that it had corroded and was in pretty bad shape. I put a new thermostat and housing on, bypassed the little coolant line to the carb (it goes to a small block of metal to help heat the carb auto choke mechanism as far as I could tell) because I am in Cali and it is never cold here, flushed the entire system out with 50/50 vinegar and water, rinsed her out twice, the filled her up with coolant, burp, fill, burp, fill, burp, fill.... And now she is a cool kat!!! What a freaking difference it has made now that the coolant system is working correctly.

Thanks for all the help guys!

All a part of the friendly service. Have fun and stay safe.