300 MXC overheating

[mboyd]

Thanks a LOT for all the feedback. This weekend I will look into the leak in the crank bearing seal. That seems to be the next thing to check. Several people said it leaking air would produce the symptoms I am having. I found out the bike sat for several years, so that might have possibly caused the crank seal to dry out or crack.

The plug looks great (light chocolate brown) and the waterflow is good after removing the stat. The gas cap is an Acerbis unit with a very simple one piece rubber vent. I tested it, and it flows air into, and out of the tank well.
I think it is getting plenty of gas and water flow.

Earlier I inspected the intake boot to check for air leaks. It looked good, but I sealed the reed cage/boot with a little high temp sealant just to be sure. It did not help. The bike runs and sounds great for about ten minutes. Then when it geat really hot the idle runs up, and it starts pinging. Thats when I shut it down. I have never taken the bike out anywhere and trail ridden with it like this, I just ride it in the street until it gets hot, then shut it off.

If it is not the crank seal, all I know to do is replace the top end, and hope it is a bad head gasket. I have read you sometimes need a different head gasket. (A white or green one) Do the KTM gasket kits they sell have both gaskets in them? The pictures I have seen looked like there was only one in there.

[Eastcoast John]

Back in the day you'd fire the bike up and then spray starting fluid around the outside of the engine. If the RPMs went up, you had an air leak.

[rleontiev]

After reading all of the messages here, I thought of first checking the spec for cooling system capacity on that bike and actually measuring the amount of coolant that the system is refilled with. If it won't hold the entire amount... This would tell you if there are any large air pockets to bleed out. Sometimes hoses hold air, which can even cause a "vaccum lock" that overcomes the water pump and will not allow it to do it's job. Not sure if this is a KTM issue or not, just throwing out ideas. If you're seeing circulation via the cap, this is probably not the problem. Whether water, or waterless; any coolant is better than too little coolant, so I wouldn't be as concerned about what it is initially. The other thing I would look at is hose routing. Did your buddy install the hoses correctly? Maybe refer to photos of service data to verify this...

[bajadog]

Originally Posted by mboyd

I have read you sometimes need a different head gasket. (A white or green one) Do the KTM gasket kits they sell have both gaskets in them? The pictures I have seen looked like there was only one in there.

Your bike has two o-rings not a head gasket, and both need to be replaced
at the same time.