You can pressure test the cooling system. You might be able to rent a kit from a local part store or you can have it tested at a radiator shop.

Water wont just evaporate from the cooling system. It has to go somewhere. Like boost said, it can be going through one of the intake manifolds. and a purple said, you can get the system checked at an auto shop eg, midas auto care, firestone, mom and pop shops or at a radiator place. or do it yourself with the kit. its pretty straight forward on how to do it, its not very difficult at all really.

Pressure test it and check for external leaks. look everywhere, at fittings, elbows, hoses and at the manifold. if none seen, then it is an internal leak aka intake gasket of some sort.

Eric.

Thank you for the help guys, and btw, no sweet smell from the exhaust. Also, according to my scangage intake air temp is 145*

The air intake temperature will drop when you get above 50MPH and should not make any difference on your cooling system issue.

My scan gauge will show about a 20F difference higher for intake air versus ext air temperature at 60MPH.