Boiling coolant resevoir

[TheChosen1]

Hey all! So the other day when I got home my 94 Mazda Navajo's coolamt reservoir sounded like it was boiling and had steam coming from the reservoir cap. The next morning, while the truck was cold, I took of the radiator cap and started the truck (to do the head gasket test) and the coolant didn't bubble or move. Any suggestions? Radiator Flush? New Radiator cap? Maybe new thermostat? Thanks in advanced!

 

[974X4BLACKSPORT]

Boiling coolant = >212 degrees F.
Steam is invisible, only water vapor is visible, neither should be present on a sealed cooling system.
There are three reasons for your coolant to boil, and they are as follows:
1) your engine coolant/water has exceeded a temperature to allow the water/coolant to exceed the pressure on the radiator cap.
2) the radiator cap is not holding to the rated coolant pressure it is designed for.
3) there is a leak in the cooling system, preventing the system from holding water pressure.
One, or all of the above reasons can exist at the same time.

 

[TheChosen1]

Boiling coolant = >212 degrees F.
Steam is invisible, only water vapor is visible, neither should be present on a sealed cooling system.
There are three reasons for your coolant to boil, and they are as follows:
1) your engine coolant/water has exceeded a temperature to allow the water/coolant to exceed the pressure on the radiator cap.
2) the radiator cap is not holding to the rated coolant pressure it is designed for.
3) there is a leak in the cooling system, preventing the system from holding water pressure.
One, or all of the above reasons can exist at the same time.

Thank you! I'll get a new cap, flush the radiator and che k for leaks.

 

[TheChosen1]

Update: The drain plug was clogged. The upper and lower Radiator hoses had fluid in them. So I'm thinking its a bad Radiator?

 

[410Fortune]

Your radiator may just need a good flush

Your radiator cap and spring pressure is what controls the boiling point of your coolant
I would try a new radiator cap and a good cooling system flush including radiator and back flush the heater core

 

[TheChosen1]

I think this was the problem lol. Sorry for the late update. Had to wait for shipping. Thanks to everyone!

 

[TheChosen1]

A backwash & half hour with a tiny jewelers screwdriver cleaning roadkill out of the fins does wonders.
Take a good look over those side tanks for any cracks\splits\leaks.
Also a good time for new cap, hoses, fanclutch, pump, thermostat, coolant...?
D

Oh I already installed the new radiator, hoses, thermostat and cap. And of course a flush. Works good now!