The coolant is hot and bubbling. The car is not overheating. I changed the water pump, the thermo sensor, thermostat and intake gaskets. Not sure if it sealed completely.

Wondering, is it the head gasket?

I tried to do the test but it doesn't work because there's no cap on the radiator. The only cap to to check it is on the engine.

  • "The coolant is hot and bubbling." how-where did you see this?
    – Moab
    Commented May 11, 2016 at 17:11

1 Answer 1


So you've replace a bunch of coolant related components and you want to know if anything leaks? You can borrow a coolant pressure tester from you local autoparts store in many locations (leave a deposit). You will place the tester on the fill cap (no matter where it is), pump up the pressure and then note the pressure on the gauge. Give it a few hours, come back and check the pressure. Is it lower than when you filled it? If so, that means a leak. Hopefully you can see the leak from one of the hoses, from a hose joint, from the radiator. If you have a leaky heater core you will see coolant coming out of the heating ventilation Air conditioning (HVAC) drain down low on the engine side of steel dash panel (right in front of the front seat passenger). Do check under the car carefully for bleed down leaks!

If the pressure at the tester decays, and you can't find the leak, check for coolant in the oil. This is bad, as it means either a head gasket / sealing issue or a crack in the engine block is allowing coolant to leak inside the engine.

You also mentioned that the coolant is hot and bubbling. I presume you mean that when the coolant temperature gets to 212F (100°C) that the coolant boils. Yes that is normal. Put the cap on the coolant system! That cap has a spring in it, that keeps the system pressurized to 13 psi or so. At that pressure water doesn't boil until 242°F. If you see (or test) that the temperature never gets above 212°F, then you will need a new coolant cap. That seal / spring pressure thing is a big deal. I would expect a normal operating temperature for your coolant system to be from 180°F to 230°F or so (with a good radiator cap.)

And if I got that coolant bubbling thing wrong, and its bubbling at temperatures below 212°F that would be bad. It would likely mean you have a crack in the engine or head gasket issue, and high pressure exhaust from the cylinder's combustion process is entering the engine coolant system, somewhere.

It's not clear on exactly what you are trying to communicate here. You just said "hot and bubbling". One awesome tool to have is a thermometer. I've used many different types (dial indicator, electronic) and broken each and every one of them. They just don't last. Best thermometer I ever had was this one. It comes in this double aluminum container, such that the glass doesn't break if you drop it accidentally on pavement.

Pocket Glass Thermometer

You can use one of these to accurately communicate "hot".

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