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I bought a new radiator cap and put it on and it is the right one for the vheicle. and it is poping off(the spring in it letting coolant out) every once and a while. May the NEW cap be defective? or may there be another problem. water pump been replaced not too long ago…. see no leaks other than at cap.
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What vehicle do you have as most radiator caps are screwed down onto the radiator or coolant reservoir.
Assuming this new cap is the proper one for the vehicle ( does it have the lever release ? ) I would check the radiator neck for possible damage or excessive wear.
Modern radiator caps are designed to ‘burp’ themselves. When hot trapped air causes a pressure rise, the big spring allows hot air to exit by way of the reservoir. The air then bubbles through the cold fluid in the reservoir, and from there it finds freedom. Then when the auto is turned off there is a second hidden spring in the cap that allows fluid in the reservoir to siphon back up from the reservoir into the radiator. Note that hot air escapes but cold fluid siphons back. That back-flow starts when cooling in the radiator creates a slight suction to open that second hidden spring inside the radiator cap. That cycle of fluid replacing air is intentionally designed, and is one of the coolest things about modern cooling system design. Once the system is purged of air, you will find less air escaping because there is less expansion with heat. Once air is purged from the system there is much more efficient cooling because under pressure the boiling point of the liquid is much higher. And also trapped air doesn’t transfer heat nearly as well, so when you first work on a cooling system it doesn’t work very well because of pockets of air inside the engine core.
What I’m saying is that it is NORMAL for the spring of the radiator to open when the vehicle is running, especially for a week or two after you work on the radiator. Unless your system is having other problems I wouldn’t worry….
Check the neck of the radiator for a broken tab or distorted flange. Make sure the engine isn’t overheating and full of coolant. (if ok see below)
You need to perform a block test to confirm you are not getting combustion gasses into the coolant chamber via a head gasket, cracked head etc.
Those gasses will cause additional pressure causing the pressure to exceed the limits of the cap.
You can get a block test kit at NAPA for about 20.00 usd and follow the instructions on the box it is real easy to do just don’t let any antifreeze mix with the test fluid as it will not complete the test.
Did you buy a quality radiator cap? If it came from AutoZ***, I would suggest getting one from the dealer, and seeing if that makes a difference.
You get what you pay for when it comes to aftermarket parts from autoparts stores. Did you inspect the radiator filler neck to see why the cap is not securing down?
Hard to say really as it could be either the cap itself or the radiator neck as has been suggested. You might want to inspect these things but also make sure your cooling system is in good shape and not overheating.
I’m sure many of us are interested to know what the problem was — don’t forget to update this thread when you get a solution.
I’ve used the brand stant for thermostats and radiator caps for years and never had a problem. hope fully your problem is solved. if not
post back. keep us posted.The system will become pressurized normally so I don’t think air is the issue but rather the ability of the radiator cap to maintain it’s seal which if it’s not is either due to the radiator neck having an issue or the cap itself, if it wasn’t doing it before you installed the new cap I would suspect the cap you never know it could have been returned by someone that bent it or something before you got it.
Eric, I think what he was saying in the intro was that air was discharging to the coolant reservoir, not directly to atmosphere. The choice of words ‘popping off’ was not exactly accurate. I can see how the description was a little confusing….
The original poster said (at the end of this thread) that he thinks in retrospect that it was air in the system. So, it sounds like the problem was a temporary one caused by trapped air discharging to the coolant reservoir, naturally burping the system.
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