coolant out the overflow

My first thought would be the coolant tank cap needs replacing.
Not sure what pressure the C-15 runs at but my Cummins has about a 5 psi cap on it.
It was doing the same thing and a new cap cured the problem.

 

Should be a 15 lb cap. Blown head gasket will cause compression to leak into the cooling system and force coolant out the overflow.

 

yeah, but a readiator cap is the cheapest, easiest to fix and the most common problem.

and i'd think 5 is a little weak. mine also says 15 but i don't have a container. i have an 05 isx

 

Older trucks that maintain a coolant temp of 180*F use a 7lb cap. As the coolant operating temps were raised to satisfy emission standards the system pressure also had to be raised to prevent boiling of the coolant hence a higher lb pressure cap on later model trucks.

 

my egr engine runs at 175. with a 15 lb. cap

the 94 d60 also runs at 175 with a 15 lb. cap.

a 7 lb. cap isn't gonna cut the mustard when your climbing a hill. and the coolant temp climbs to 22o.

 

Easiest way to check is to fill a soda bottle with water and place the overflow hose in it and check for bubbles while it is running. This will tell you if you have compression filling the cooling system.