I've got a 97 5.2 and it's only when I start it for the first time everyday there's a water swooshing noise. But everytime I start it after that it doesn't make the noise. I've been having water in the passenger side floorboard so I don't know if that has something to do with it or if there's air in the cooling system. If there is air in the cooling system would that affect my temp gauge?

 

Because the temp gauge quit working yesterday

 

Also everytime I fill up the coolant reservoir, it disappears a day later, it's not leaking. I don't know if it's all related

 

I suspect its leaking onto the passenger floor.

 

You need a heater core at the very least.

You can/could tie the heater hoses together in the engine bay, top off the system and see if all your problems disappear. I suspect they would. But you'll have no heat until you R&R the core.

 

Usually water on passenger floor say heater core is leaking from my experience.

 

Is it just water or coolant(antifreeze). If you put the heater on and smell antifreeze it's the core. Check the water drain on the firewall(AC) the gasket deteriorates and allows the water to drain back into the interior.