Quote Originally Posted by ipd View Post
Well it seems I'm back to square one. Overflow tank is boiling again. Was only bubbling sometimes, but steam was coming out of it tonight when I parked it. Drove fine from AZ up to UT without issue. Had an oil change & I think they may have added coolant in the process. I'm really not sure what's causing it though. Oil level still reads fine. I'm at my wits end.
Have you ever changed your radiator cap? The purpose of a properly operating cap is to increase the pressure in the radiator/cooling system to allow the coolant to reach it's designed boiling point.

What is your coolant level in the radiator itself with the radiator cap off and the engine running at normal operating temps (the coolant/engine hot enough to open the thermostat)? It should be up near the top of the tank when looking into the radiator cap opening. I wouldn't just trust what the reservoir level is telling you anyway since you may have an air pocket elsewhere in the engine.

You could also try adding the aftermarket product Water Wetter. It increases the surface tension of whatever coolant you're running, effectively increasing it's boiling point.

I'd have my doubts that you have a head gasket issue if the engine so far has been running evenly, but you could always have your cooling system pressure checked (with one of the gauges that installs where the radiator cap usually goes) to determine if you have any air leaks in the cooling system.