Coolant filler neck mystery seal?

[Muddy]

So I recently got myself a 2004 4x4 Sport edition, and this weekend got around to doing a lot of the basic maintenance/fiddling around that comes with a new (used) vehicle. Upon going to replace the radiator cap (coolant cap? Its not on the radiator so...) I noticed something odd and wondered if this is normal for Libbys or not.

Inside the filler neck where the cap goes on, (not on the actual cap itself, but down inside the bottom edge where the bottom of the cap seats against) there was a badly cracked and broken rubber seal. I haven't seen anything like this on any previous vehicles, and was wondering if it was normal- in my experience the rubber seal on the spring-loaded portion of the radiator cap seats against the metal or plastic of the filler tube, so a double seal seemed off to me. Is this a part that I need to replace, or will the new cap seal against the ring inside the filler neck on its own?

 

[HoosierJeeper]

The seal from the bottom of the cap just broke off and is laying there. New cap will fix it. Probably pulled off when you took the cap out, happened to me.

A Mopar one is a safe bet. Just use whatever part number it says on yours. Some got an 18 PSI one others got 16 PSI. I brought an identical Mopar one for $12 on eBay. Mine took a 16PSI one. Some books say 18. You can get a Stant one locally for $5 or so, that'd be fine in the mean time (or permanently most likely).

 

[Muddy]

The seal from the bottom of the cap just broke off and is laying there.

See I had that same thought at first, but the seal was still attached to the old cap when I pulled it off. Also upon pulling the seal out of the filler neck and comparing it to the one on the new and old caps, it's a different design- not just the flat rubber ring that the caps have.

In any case, as long as the filler neck isn't supposed to have its own seal at the bottom, I'm fine throwing this broken one away and forgetting about it! Just wanted to make sure I didn't need to order any other parts.

 

[HoosierJeeper]

There's two seals on a cap. One on the bottom then one close to the top of the cap.

 

[Muddy]

There's two seals on a cap. One on the bottom then one close to the top of the cap.

Yeah I know this. The place I'm talking about is the lower seal area, where the spring loaded plunger seals against the bottom of the filler neck, not the one up around the top edge of the cap. Both seals were still intact on the old cap though.

 

[HoosierJeeper]

That is weird. Does the seal you found match in diameter/hole size with the bottom seal on the cap? I'm guessing that seal fell off the cap and then someone replaced the cap and didn't take the old seal out. Is it a Mopar cap?

 

[Muddy]

You must be registered for see images attach

Here's a pic of the old cap and the mystery seal that came out of the bottom of the filler neck. The seal in question is narrower in profile than the one on the bottom of the cap, and is molded in an 'L' shape such that it's wider around the edge and then has a flat lip in the center section where the cap was seated against it.

The old cap is a Motorad, the replacement is a Stant.

 

[HoosierJeeper]

That is weird. I have never heard of a gasket in the neck. I can check mine tomorrow if you'd like, but I'm 99% sure that's left over from a previous cap.

 

[Muddy]

Yeah if you could give it a quick look sometime today that would be cool, thanks. In any case that old cracked mystery seal clearly wasn't doing anything to help hold pressure in the condition that it was it so I'm no too worried about it :laughing1:

 

[HoosierJeeper]

I literally can't find a part number or mention anywhere of that gasket. It's got to be from an old cap. You already know it's been replaced once.