so recently changed my hoses for my heater. after i changed it everything was fine but i had a slight coolant leak at the firewall and i think my heater core is leaking coolant also. anyways why is my coolant boiling.

 

It's boiling into the overflow tank? If you remove the filler cap with the engine idling cold, does it bubble? If so, that points to a coolant seal leak.

You may also want to flush the coolant system if it's not a 50/50 mix.

Stock radiator cap? Offhand I think it's a 13psi cap.

 

I can hear it boil in the radiator and also the reservoir is hot.

Why does the radiator cap matter?

 

different radiator caps have diff boiling limits it can handle, certain psi levels arent as healthy to use as others, such as 9 psi ( i believe is worse) then 13 psi

 

Pressure testing the coolant system and cap might help to figure out if you have a leak. If the coolant system can't pressurize then it can't raise the coolant's boiling temperature so you will hear the coolant boiling.

 

do you have anything to read the temp besides the stock gauge? after you hear it boil, do you know what the stock gauge is reading? if its above 9:00 thats not very good

 

Thermostat stuck? Fans coming on?

 

Could it also be air in the system from when he replaced the hose?

 

I'm having a similar problem on my N/A 87, I've only had this problem after I flushed the radiator and refilled with fresh 50/50 mix a few days ago, here is a video of the problem

 

air

 

let it idle from cold with the radiator cap open and watch for the coolant level .

 

try an apexi radiator cap for the rx7.... some caps dont give u a tight seal. what type of radiator are you running

 

Bone stock

@flaco, what do I do while I'm watching the coolant level?

 

Watch to see if the coolant level goes down. He was saying that you may have air bubbles in your system.

 

It was the radiator cap, but per all of your suggestions I burped the hell out of the coolant lines before I filled 'er up and she's running fine. Thanks!