Radiator cap gasket

I filled my radiator with water (for flushing) and mounted the testing kit on (MityVac or some such brand). I started pumping but the gauge wasn't going anywhere so I thought there must be a leak somewhere. When I took the testing kit cap off, the water level in the rad was nevertheless the same, meaning that the leak must have been somewhere above the water level so I then I though the testing kit cap was leaking and confirmed that was the case when I neared my ear to it and heard hissing as I was pumping. But the testing cap was brand new so it alone shouldn't really be leaking.

Then I took a look at the radiator intake opening (the one over which the cap goes) and remembered that when my engine overheated some time ago, as the recovery tank was boiling, there was steam coming out of the cap as well and, after the thing cooled down, I removed the cap and I remember there was an gasket that was sitting between the mouth and the cap but was not a part of the cap and was in a bad shape so I threw it away. I was away from home and drove back nearly 200 mi refilling the rad with water as it was leaked out every 30 mi or so.

Could it be that, as the pressure was building up in the coolant system, the cap itself without the gasket was not holding it sealed so the steam would escape, emptying the coolant system? Could it also be that the testing kit cap leaks because that gasket is missing as I explained above ? I went to RockAuto to look for that gasket but they didn't have any, I wonder if it comes with a rad cap replacement ? Or should I look elsewhere to buy it. That gasket is plain rubber donut shaped and it looks and works much like a garden hose adapter gasket.

 

Figured you would have put this in your original thread that numerous people are helping you on.

 

Which cap are you talking about? In your original post you put water in the overflow rather than the radiator if I recall correctly.

The tester should hiss, it's pushing air into the system to pressurize it.

The silver cap that actually goes on the radiator should have a rubber gasket, if not you'll probably have to buy a new cap assembly. Without that gasket it's not going to seal and you're going to boil off water at a lower than designed temperature.

Why pressure isn't build when you test the system; Does the tester have it's gasket? Is the tester installed correctly? Are the hoses connected well? We had a pressure tester that was a little finicky and you had to make sure the hoses were on nice and snug. If all that checks out then yes you have a leak in the system somewhere and if you have water all the way to the fill neck then you should be seeing it leak out somewhere although it's going to be harder to see if it's a small leak and you just have straight water.

 

https://www.tacomaworld.com/threads/engine-overheats-coolant-level-drops.374514

 

Like I said, it is the proper cap (radiator cap), not the plastic resi tank.

Like I explained, the original in-between gasket has not been replaced and hence my suspicions, one of which is that its absence is causing the tester cap to leak (as the tester cap alone doesn't seal it)

 

If you're testing the cap without it's gasket then it's going to leak.

 

It's okay to have this as a separate thread because it could be its own topic

 

Yes, this was exactly my hypothesis. Thanks for verifying.

Do you know if the gasket comes with a new cap or does it need to be procured separately? I doubt it was actually a part of the cap but could be, when I had my overheating, it may have melted off and stuck to the opening before I ripped it off.

 

The new cap will come with a gasket.

 

There is no seal that is not a part of the cap. From your description, it sounds like the "inner" seal that holds pressure and opens to allow coolant to flow between the reservoir and the radiator. Without it your system won't pressurize and will overheat every time. The cap was suggested a few times in your original thread and it's like a $10 part. That would be the first thing to replace based on the symptoms...

 

It makes sense that the gasket is part of the cap but it doesn't explain why the tester cap is leaking because I thought it was supposed to sit there when the cap is off and the absence of which was causing the tester cap to leak because it alone doesn't seal it.

 

Maybe it wasn't a rubber gasket but a plastic top of the opening that was part of the rad but melted off... Just an idea

 

Take some pictures man. Then we can get a better idea of what's going on.



This, and every cooling system tester I've used, will have a gasket like the one that goes on the cap to test the system. The adapter on the top right is used for the cap and that one needs a good gasket to seal otherwise it will leak as already stated. It could be that your new tester is defective, wouldn't be the first time.

 

I just updated the OP and attached a picture of my rad opening, which I'm suspecting of missing the top plastic contact surface.

Perhaps it would be helpful if one of you could post a picture of your healthy one for comparison.

 

You have a gasket that seals the smaller inner surface which is spring loaded to allow excess to drain into the overflow tank and an outer gasket that seals the radiator and allows it to build pressure.

 

Is that red outer ring (that's in between the two black rings) a gasket or spillover coolant ? I'm asking cause it's the same color as the coolant in the bulls eye.

If that's a gasket, it would be the one I am missing.

 

No it's coolant. There are only gaskets on the cap.

 

OK. So by looking at my picture, can you tell if anything is wrong with it ?

 

The gasket is part of the cap. looking at the picture it appears that the ring in the radiator is either badly pitted or has a bunch of crap stuck to it so the cap or tester can not seal try a new cap and clean or smooth the surface in the radiator that it seals to.