was running hot so I added coolant. now the gauge is going up and down slightly and the heater doesn't blow hot air. a.c. seems fine.

HI mikelj80, you probably have an air pocket in the cooling system, keep overflow tank checked and add coolant as needed. Does your engine have a bleeder valve? Sound like you may have a leak.

I've read of folks "burping" their cooling system by positioning the front/passenger side of the truck much higher than the rest of the truck with the engine running cold & the radiator cap off, keeping the radiator topped off until the engine gets to normal running temperature, then installing the radiator cap.

A bad radiator cap can keep the cooling system from building normal pressure too.

Just remove the radiator cap while cold and start it up. Let the engine get to operating temps and add more water/antifreeze.
You have air in the system and you will continue to hear it until you get rid of it.
If it continues then you have a leak in the system.

I've read of folks "burping" their cooling system by positioning the front/passenger side of the truck much higher than the rest of the truck with the engine running cold & the radiator cap off, keeping the radiator topped off until the engine gets to normal running temperature, then installing the radiator cap.


+1, that's how it's done. It's a PITA to get the air out of the system on these rigs.