any cap or valve system has to do 2 1/2 things..

first....maintain pressure on the coolant, and release pressure if it
gets too high.

then,
Have a 'suck-back' feature from the license plate / overflow bottle.

just a one way valve won't do all that.

I installed a Van Cafe-  supplied all aluminum pressure tank with
conventional 'american style' pressure cap.
it was almost 100 % perfect in design and execution.
Don't know if they still sell them, that was a few years ago.

On 10/14/2015 7:25 AM, Eric Wunrow wrote:
>> Yes, mine are from Meyle.
>>
>> Jim, your inline valve idea is great!
>>
>>   Eric
>>   Eric Wunrow Pictures
>>
>>   303. 988. 8717
>>   VW@EricWunrow.com
>>
>>
>> <EW Email Sig.gif>
>>
>> On Oct 14, 2015, at 8:08 AM, Jim Felder <jim.felder@GMAIL.COM> wrote:
>>
>>> You are exactly right, the one-way feature on the valve is something I have
>>> know VW shops to argue about. When I had a 2.1, I would test them before
>>> leaving the parts place because so many of them didn't work out of the box.
>>> The "good" ones didn't last long, either. I suspect you might be buying a
>>> brand called "Meyle Germany" but that is just the brand name some company
>>> bought, and they could be made absolutely anywhere. You might try the
>>> dealers but good luck with that.
>>>
>>> One of these days, all vanagon drivers are going to be using that cap
>>> simply as a connection to a one-way valve from a third party, inline
>>> between the reservoir tank and the overflow tank.
>>>
>>> Jim
>>>
>>> On Wed, Oct 14, 2015 at 2:41 AM Eric Wunrow <VW@ericwunrow.com> wrote:
>>>
>>>> I'm a total rookie compared to you guys, but wanted to note I've had at
>>>> least three expansion tank (blue) cap failures in 23,000, full-time miles
>>>> over 26 months on the road. I believe the failures are somewhat related to
>>>> how many heating/cooling cycles they're asked to do.
>>>>
>>>> I only buy the German ones, and my test is if you can both suck and blow
>>>> on the cap, it's toast (please keep the jokes to yourself).
>>>>
>>>> My understanding is the cap should only release pressure one direction �
>>>> not two.
>>>>
>>>> Eric
>>>> Eric Wunrow Pictures
>>>>
>>>> 303. 988. 8717
>>>> VW@EricWunrow.com
>>>>
>>>>
>>>>
>>>>
>>>> On Sep 28, 2015, at 3:27 PM, Stuart MacMillan <stuartmacm@GMAIL.COM>
>>>> wrote:
>>>>
>>>>> Thanks Jim, the cap was replaced with an OEM cap when the water pump was
>>>> done 13,000 miles ago, and the overflow tank doesn�t show any evidence of
>>>> any spillage on or under it.  I�m thinking small leaks too, but I�d like to
>>>> narrow it down.  The 2.1 has a lot more hoses than my 1.9!
>>>>>
>>>>>
>>>>> Stuart
>>>>>
>>>>>
>>>>>
>>>>> From: Jim Felder [mailto:jim.felder@gmail.com]
>>>>> Sent: Monday, September 28, 2015 2:21 PM
>>>>> To: Stuart MacMillan; vanagon@gerry.vanagon.com
>>>>> Subject: Re: Missing coolant
>>>>>
>>>>>
>>>>>
>>>>> Old hoses leak microscopic amounts of coolant. Ive had it spray onto the
>>>> engine in such small quantities that it would evaporate before you could
>>>> see it. Tighten hoses, replace hoses is about all you can do. But you
>>>> didn't mention testing the pressure cap. That can send a good deal of
>>>> coolant into the expansion tank, which can drip on the road through the
>>>> overflow and you won't know it.
>>>>>
>>>>>
>>>>> Jim
>>>>>
>>>>>
>>>>>
>>>>> On Mon, Sep 28, 2015 at 4:11 PM Stuart MacMillan <stuartmacm@gmail.com>
>>>> wrote:
>>>>> Just when everything seems to be sorted out, it isn't.  Son's '87 is
>>>> losing
>>>>> over a quart of coolant every 400 miles, and I can't find any leaks.
>>>> Rear
>>>>> heater has been removed, and there is no odor from the front heater.  No
>>>>> drips anywhere-engine plumbing, heads, transmission cooler, radiator, or
>>>>> front heater valve.  No evidence of coolant mixing with either the
>>>>> transmission fluid or engine oil, and that much coolant would certainly
>>>> foam
>>>>> oil.
>>>>>
>>>>>
>>>>>
>>>>> I'm wondering if it's burning coolant, but in my experience failed
>>>> sealing
>>>>> rings in Vanagons lead to over pressurization of the system, and that's
>>>> not
>>>>> happening. It also runs great. I sometimes notice a faint smell of
>>>> burning
>>>>> coolant at the engine compartment vents, but I can't find anything
>>>> dripping
>>>>> on the exhaust when the system is pressurized.
>>>>>
>>>>>
>>>>>
>>>>> Would investing in a UV leak detection kit tell me anything?  It would
>>>> seem
>>>>> losing this much coolant would show up somewhere.
>>>>>
>>>>>
>>>>>
>>>>> Any ideas?
>>>>>
>>>>>
>>>>>
>>>>> Stuart
>>>>>