overheating

I noticed you said you are losing water into your overflow tank. It's possible your cooling system is being over pressurized and forcing water out of your radiator and into your overflow tank. You may want to run a compression check and check to see that all of your cylinders are reading consistent PSI numbers. It's possible that you have a leaking head gasket. I only mention this because you said the cooling system had worked fine in the past. Let us know what you find out.