I've replaced the radiator cap. The radiator is new and I even got a new coolant level sensor. When pressure builds up, the cap pops and coolant comes out. Is there too much air in the system? Is something defective with the cap?


Her is the video on Youtube. It pops at 9 seconds:

 

I take it this was happening with the old radiator cap as well? Is it the correct rating, 18 psi. Could be you have a faulty new cap (not holding pressure/not sealing well), could be you have a blown head gasket building up too much cooling system pressure. Any other strange engine symptoms?

 

Thanks for the quick reply! No other strange symptoms. The cap says 18 PSI right on the cap and yes this was happening with the old rad cap too. Oil level is fine and oil is nice and clean. Changed the oil in June. Car has lots of power, took it to get some gas today after I changed the coolant level sensor. The old sensor kept telling me I had low coolant when I didn't. This issue was happening before I changed the coolant level sensor too.


Here's a pic with the rad cap and one without the cap on:

 

Update: A friend of mine told me my thermostat probably isn't working. Is this possible?

 

What is your temperature gauge reading? The engine will overheat if the stat is stuck closed. Does the cap just spray once like that, keep popping intermittently, or finally come to a huge blow?

 

It keeps popping periodically. The car runs hotter than usual. Goes to almost 3/4 of the way up then cools down back to the halfway mark. Been like that since I got the car. Lately the car has been keeping cool better. I wonder if it's a thermostat that's sticking? I'll pick up a thermostat and replace it anyways since I never replaced it and have no idea how old the thermostat is. It's not a big investment or hard to change.

 

I replaced the water pump and put in a new thermostat. The rad cap is new too.


The problem is now when the system builds up pressure, coolant is leaking out of my rad cap! Is it air in the system? Bad rad cap? The upper and lower rad hoses are new too.

 

Was the air purged out of the system after refilling with coolant?? Overflow coolant should not be leaking out but should be going to the overflow container, is the passage from the radiator neck to the overflow container clear? Could be the wrong type cap for the radiator. Thermostats are built to fail in the open position and "usually" do not fail in the closed position.
May want to have coolant tested for the presence of combustion gases to make sure there are no head gasket leaks.

 

It has to something with the overflow it is not working right. Even in the worst case of a blown head gasket it should push the coolant and/or gas into the overflow. I have seen many overflows looking like an erupting volcano and they did not leak there. I would replace the cap and check the overflow hose to make sure it is not pinched or plugged.

Was there any sign this was leaking with the other cap? If the overflow is blocked off you coolant will go somewhere and since it can not pull coolant back out of the tank your radiator will always look low.

 

I had an epiphany! Gorn, you sparked it! I did something dumb. I replaced the overflow hose with fuel hose. As you know it goes under the battery. The fuel hose is thicker than the overflow hose that was there, so there's a good chance it's kinked. Luckily the parts store is in walking distance so I'll head there in the morning and get the right hose and some clamps.


Z28pete the cap is an aftermarket metal one and I heard that it isn't a good mix with the plastic rad neck as it will scrape the plastic over time. I'll try the old factory one I kept from my V6 Camaro. It's the same PSI 18lbs. The metal cap is the only one the parts store sells.


Thanks for your help guys!