Open the radiator cap (when it's not hot) and smell it. If it's smell like gasoline, you've got warpage in the housing as the rotor goes through its induction phase. The motor is drinking coolant like a Russian at a jet fuel depot but man it runs great though.

 

Maybe we should hook a high pressure pump up to the cooling system so it pumps coolant INTO the motor while it is running. We can use it like water injection. Turn what would otherwise be a real downer into an upgrade :p

 

a conclusive test is to test for hydrocarbons in the coolant while the car is running. any decent shop should have the testing equipment. basically they place it over the water filler neck and if the solution changes colors then there is exhaust in the coolant. checking the plugs and little bubbles coming from the filler neck are nice but not as good.