I had a nice drive through town today, around 80 degrees outside and my temp stayed at dead center all day yet when I got home I heard an odd noise from the engine bay. After opening the hood it was freaky/interesting to see the overflow tank boiling like mad. What could be the cause and should I be worried?

 

Either a bad/closed thermostat, cooling fans not working or low on coolant.

If you keep driving it like that you could hurt your engine.

 

If you radiator cap is not holding pressure, that will also cause the water to boil at a lower temperature than when it has 15 psig on it.

 

Coolant level is fine as is the fan. How can I check either the thermostat or radiator cap for if they are working properly?

 

You could just replace both, as they aren't very expensive. To check your thermostat, you can take it out, put it in a pot filled with water on the stove, put in a temp gauge, and watch it open at the correct temp. I would spend the 8 bucks on a new one though. The radiator cap? I don't know how to test that. The spring or gasket is probably worn out or something, and if it's never been replaced, it's probably due. Those are good places to start. Also, how does that coolant look? Clear? Murky?

 

Every one of these cars that I have owned has done this. Replace your radiator cap.

 

that's the excess coolant getting pushed out of the radiator as it expands when it gets hot- it bubbles because it boils when it leaves the 15psi radiator and hits the atmospheric pressure in the coolant tank... don't worry about it unless the car overheats and/or loses coolant.

 

You can get a loaner coolant pressure tester & test the radiator cap.

 

^^ Yuuuuuup, it will instantly boil if rad temp is above ambient boiling temp

 

The easiest way to tell if the thermostat is bad and stuck closed
is to check to see if you have heat.
No heat means a bad thermostat....................

 

If the motor isn't hot, i.e. the gauge reads normal, the thermostat is fine. Leave it alone.

You need a radiator cap.

You test radiator caps by substitution. Specifically, you substitute a new one, and discover that the old wore-out defective one was not holding the correct pressure because the spring was rusted out and the rubber seal had disintegrated, and was venting steam.

 

I know how an overflow tank works, I'm not completely car-tarded, but in 5 1/2 years of this car being a daily driver, including me driving it to a track 30 miles away, all highway, with a 3 speed auto and the engine holding at 3500-4000 rpms for most of the drive and 100+ degrees outside that I have never once seen it actually boil like that. I've seen it expand as usual but not once boil. I will change the radiator cap and hopefully the boiling stops. I may be paranoid but it does look like my coolant has dropped a little.

 

it would be easier to just touch the upper radiator hose.. if it's not hot when the engine is hot, then the water isn't flowing... of course, if this happens the gauge will be pegged hot before too long.

 

I feel like my upper radiator hose has always been hot whenever the car had been running, should I be concerned then?