Coolant disappearing act

Need some advice on tracking down a coolant leak. I have an 06 yz450 which has started losing coolant somewhere. Here is situation : coolant needs topping off 2-3 times a day at the track, no visible signs of leaks, no coolant in oil last time changed, can not smell coolant being burnt coming out of exhaust, and I tried another radiator cap already and didn't change anything. Any advice before I pull the head would be appreciated.

I think you can get a dye that will allow you to see it much better. Pretty sure its sold at local auto parts stores.

When you say topping off, what do you mean? As long as the coolant stabilizes above the fins, that is good. In Texas during the summer I boil over about 1/4 cup from full and then it stabilizes...

The level drops below the top of fins that can be seen, needs quite a bit more than 1/4 cup to refill.

The engine can loose coolant internally without mixing it in oil in only a couple of ways, either via a leaking head gasket or a crack in the head or cylinder into the combustion chamber. Before you decide that's the problem, be sure you aren't chasing an external leak. Two sneaky places to loose coolant are at the cylinder head water outlet pipe and the water pump. The outlet pips O-ring may seep under pressure, and the water pump seal can leak only under certain conditions if it feel like it.

One good way to track coolant leaks is to dust the suspect area with baby powder or foot powder. Leaking coolant will leave a distinct trail in the powdered surface, even if it can't be detected. Also, in the case of the water pump, the woven cover on the oil reservoir pressure balance hose that runs just below the pump may be damp and smell of coolant.

Something to watch for with water pump leaks is shafts with grooves worn in them by the seals and loose balancer shaft bearings:

http://www.thumpertalk.com/forum/showthread.php?t=785425

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