Sunl SL250-22 Cooling Issue

[Crash4723]

Originally Posted by bnc

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.

[bnc]

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.

[kz1000st]

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.