Well i don't think it's a head gasket cause it's not smoking at all and is still running good. There's no coolant in the oil either.
tcb5040, You're asking for our help and now you're disputing what we are telling you?!

You said in your first statement you'd been dealing with this for weeks and couldn't figure it out.
I was confident, (and still am) when I first read your post that the head gasket was most likely culprit, if not a stuck thermostat. I was hoping you might get lucky and have a bad stat but: But a stuck thermostat would not create enough pressure to blow off the cap on the overflow tank. It is a screw on cap yes? Radiator caps sustain about 15-30 psi at the radiator before they will boil over or allow the pressure built up in the tank to compress the spring and then coolant flows back to what is actually an expansion tank; commonly called overflow tank.
Numerous people have told you the same thing- likely blown head gasket with exhaust gases rerouted into the coolant causing overheating; so much so that it blew off the cap on your overflow tank!
You say that because its not smoking and there is no coolant in the oil that it is not a head gasket. Those checks I suggested are to rule out things including and beyond a head gasket. Keep running it and you will see smoke eventually and may end up with coolant in the oil- but less likely since it (coolant)is being burned by exhaust gases, and the gas is escaping out the cooling system to atmosphere at your overflow tank.
Its your tractor and you can do what you want, but I can assure you that if you continue to do what you've been doing it will cost you.
If I'm wrong so be it. But if I'm right, {and my having owned an run a foreign car repair shop for over ten years favors me being right}, then it might be wise to heed my advice and that of others who are trying to save you butt and wallet from bigger possible expense.
Caveat to above: assisting anyone via the net is ok except it does not substitute for being in front of the tractor/vehicle and seeing what is actually happening. I've had people tall me all kinds of things that were wrong with their expensive foreign cars and I actually started a list of famous one liners to showcase the amazing gap between what customers thought was the problem and what the actual problem turned out to be.
I'll be interested to see what your situation ends up being in the end result.
Oh, btw, since you are convinced its NOT a head gasket what is it in your opinion? This I've got to hear
