Expansion Bottle

[Robbie Roadster]

Team,

I noticed when removing or fitting the pressure cap on my MK 2. I get some movement between the Brass collar on the expansion bottle itself. Not flapping about of course but obvious when I hit the stop the collar moves.
I'm thinking this is bad as I assume this should be an airtight seal or what is the point of having a 20lb pressure cap if the air can leak around the neck of the bottle? If anything expansion when it warms up seems unlikely to help as if anything the brass likely to have a higher coefficient of expansion than the plastic bottle and thus making it worse not better.
Or are they all like that and I have I missed something?
Thanks

[NeilR]

Should be a tight crimped fit, no point in having a pressure cap at all if it isn't.
I believe it's a common problem. (Have a header tank myself - Merc W124).

[MikeParker]

I know it is disconcerting, but there is an o-ring between the brass collar and plastic bottle body that maintains the seal even when there is rotation (hopefully). Mine did have a leak at that point because of a defect in the plastic bottle that the o-ring couldn't bridge. Cure was to grind the defect off and re-crimp.

[Lingen]

Robbie.
A common fault as has been said., and it does have to be a perfect seal for the system to work at all. You could test it by removing the bottle and putting the cap and neck in a bucket of water. Then pump some air in through the rubber pipe with a foot pump or small air compressor and look for bubbles.
If you need to buy a replacement, test that as well!!
Mike.

[jbuckl]

Robbie.
A common fault as has been said., and it does have to be a perfect seal for the system to work at all. You could test it by removing the bottle and putting the cap and neck in a bucket of water. Then pump some air in through the rubber pipe with a foot pump or small air compressor and look for bubbles.
If you need to buy a replacement, test that as well!!
Mike.

+100

Imho this fault is a root cause for many cooling woes.
A new expansion bottle may also not be sealed either.

Because it’s so important…. Many do go for a header tank.

it’s possible to clean & seal the original expansion bottle though.

after cleaning, the joint should be dried for 30 minutes at 50 deg. C. or so.

then the bottle can be placed brass bayonet down & the gap filled with suitable runny glue… or loctite wicking agent.

But it is important to pressure test it afterwards.

Fwiw, have found a few speciallist supplied header tank kits :-
1. Incorrectly plumbed in.
2. Leaking pressure.

Expansion bottle or header ?

It matters not that much.

So long as they are plumbed in properly & pressure tested.

[Lingen]

The great advantage of a properly located and plumbed in header tank is that keeps the cooling system full to the brim at all times, even if it isn't pressurised.
Mike.

[022Dave]

The great advantage of a properly located and plumbed in header tank is that keeps the cooling system full to the brim at all times, even if it isn't pressurised.
Mike.

Oh, you’ve done it now, Mike. Watch the venom flow…

Dave

[Lingen]

Good morning Dave. Let it flow. At my age I am used to it!
Mike.

[Wheelz]

The great advantage of a properly located and plumbed in header tank is that keeps the cooling system full to the brim at all times, even if it isn't pressurised.
Mike.

Fact, but many will still not believe it......