Expansion caps, real OEM or not.

As this is a continuing theme on the forum,  I thought a bit of scientific examination was called for.
I bought a genuine (Rimmer bros) expansion cap and another eBay bargain, which was half the price of Rimmers.

Here they are together. 

And the insides.   NOW THEN:- Which is genuine and does it make any difference? 

I tested both with my pressure tester setup. 

Results:-  1 held around 14- 15  psi,       

1 held around 6 psi.
 

Which is real?
 

Incidentally the Real one came in this packing from SAIC

So genuine Chinese rubbish is better than aftermarket Chinese rubbish!

Aay up David . Ive just bought one of those caps from Rimmers for our MPI classic Mini and it came in a SIAC bag . My question is,  which one of yours failed ?  Since I retired from the motor trade I do find that I miss the equipment like your tester for cooling systems.  Took it all for granted while I was working . I might have to invest in one of those if the caps are of such bad quality.     
John 

The SAIC cap is the good one!
The one on the left.

 

This is the pressure test kit I have.



You do need to make up a threaded adapter to test caps as opposed to testing the entire system.

I might have to invest in one. 👍

Thanks David for doing this little test, truly surprising. I'm glad I've always paid the extra for a genuine cap from Rimmer.

If you don’t have the adaptor to test caps you can use two coolant tanks joined together with a couple pieces of hose. Put the cap under test on one tank and something like the Laser pressure tester on the other tank and pump away.
Nigel