My sons bike is running at 100 degrees. Bike overheats within 3km of riding. Have checked for leaks and had to replace water/2 stroke tank as had a hole in. Have checked thermostat as well and works correctly.

Where is it leaking from? If its leaking, that's more than likely why it doesn't run right, the fuel/air mixture is off. Also, I wouldn't continue to run it until the leak is fixed as it may damage the motor from not lubricating properly.

try running with just water. Anti freeze lowers the boiling point while raising the freezing point.

The only oil that can leak from iside your engine is from the gearbox. There is no sump as the engine is lubricated by the oil fed in through the induction system. Clean the area thoroughly and leave it for a while(overnight) then check again. The oil could just be overfill from the 2-stroke tank. By cleaning it first you are given new evidence to identify the leak point. Hope this helps, when you have more info let me know.

If you are riding a dirt bike you probably have a leaking water pump seal allowing transmission oil into the antifreeze. If the motorcycle is a four stroke street bike the leak is probably in the head gasket.

After letting a bike idle for 30 minutes it would make me suspect that the bike was overheating...its not good to let a bike idle that long.. this is one of the two reason that California lets bikers split lanes... one is motorcycles will take up less space in traffic and the other is that it gives a chance to keep the bikes engine cooler with a constant airflow over the engine.
Now , #1 check radiator coolant level, if low, top it off with coolant. #2 if the bike idles fine after "approx". 5-10 minutes ( normal operating temp)...and your not overheating, then continue to let it idle till it gets to "around" 185 degrees or so..if you don't hear the fan come on, then get on your bike and ride it around the block to cool the engine down, if that helped then you know its a bad fan, or bad thermostat/fan switch. The trail of water you saw could also have come from the coolant overflow tank hose at the bottom of the bike when it was overheating...make sure that the coolant reserve tank is filled to the appropriate level. Also check your oil to make sure that it doesn't have water in it..if it does...it"ll appear like a bubbly milkshake; if the oil is good, then chances are good that at least no internal damage was done. If after all this and it doesn't overheat and the fan comes on! then you"ll have to pull your fairings and check "all" the hoses for leaks. Hope this helps you out. Please can i get some feedback on this and let me know if this helped. thanks!

Take the bike back to the dealer. The problem with KTM bikes is that they are so highly engineered that most riders, ( and most dealers ), have a problem getting them tuned properly. Since the bike is new, the carb should not be the problem. Don't mess with it. Have the dealer check the radiator for proper coolent level and coolent flow. If the bike has a fan, check the sensor and fan operation.

Can I get a “very helpful” rating on this answer?

NGK brand spark plug BR8ECMVX is the stock plug for the bike. The proper gas / oil mix is 32 to 1. That means 4 ounces of 2 stroke oil per gallon of gas. The posting was not clear as to just what the problem is. If you are burning up plugs there may be a air leak in the intake system making the bike run lean. A lean fuel mix runs hot.

ya i have a yz250f and learned from a first hand experience that any racebike 2 stroke or 4 stroke doesnt like to idle for a few minutes without moviing. i started up my bike and let it sit for 8 minutes to warm up and antifreeze started spewing out. so i cut it off and called a friend that races. he told me these bikes need air moving through them otherwise they overheat easily and the antifreeze over flows because it expands. if i actually read the manual the book says not to let the bike stand and idle for more then 3 minutes cause after that amount of time it should already be warmed up.
so its just the bike over heating and make sure to top off your coolant the next time u ride

Check the thermostat in the bike it may not be opening at all sounds like it is not working and also check the water pump as well

Is your fan kicking on when your bike starts to get hot?

On my cbr the fan would kick on at 215 degrees. Even sitting in traffic on a 90 degree day my bike would only get up to 220 at most.

If your fan is kicking on when its suppose to and you have your radiator filled up full then I would check your thermostat.

The thermostat is an object that opens up when your engine reaches a temperature of around 180 degrees and lets antifreeze run through your engine to keep it cool. If the thermostat isn't opening up then the antifreeze isn't circulating through your engine, its just sitting inside your radiator. And that's not what you want.

You can remove the thermostat from your bike and put it in a pan of water and heat the water up with a candy thermometer in the water and you should see your thermostat open up at around 180 degree's. Just do this on the stove. The water won't be boiling so you will be able to see it open up.

Hopefully its just your thermostat because they are very cheap(around 10 bucks).

If your thermostat is good and your fans kick on when they are suppose to then I would say its a water temp sensor or a sensor period.

I'll bet though that if you take your bike for a ride and when it gets around 215 degrees that your fan isn't kicking on to help the motor cool back down.

Hopefully this is the case and if it is you can just run the fan wires to your battery and hook up a toggle switch to turn your fans on whenever you please. This is just a bandaid fix and not fixing the real problem but it will get you by until you can fix it the right way.

Well I hope I may have been of some assistance and good luck,
Remember to check your fluid while the bike is running and warmed up completely, because if you just fill your radiator with the bike turned off it will only fill your radiator with fluid and not your motor as well(because the thermostat will be closed) which is what you want. Also after you fill your radiator when the bike is running and you can fill it any more let the bike run for a little while with the cap off to let any air in the cooling system purge out of the open radiator. You should see some air bubbles coming out of the radiator cap hole. If you have air in the system that will cause your bike to overheat as well. Had this happen on a Honda Car.

GOOD LUCK,
AadoubleA

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