TheSamba.com :: View topic - Bad Coolant Expansion Tank Cap

Sat Jul 04, 2020 12:25 pm

Just found this excellent article https://intrepidoverland.com/testing-coolant-pressure-caps/ about pressure testing and understanding coolant expansion tank caps. My cap's return valve seems fine, but the pressure containment valve which allows coolant back into the reserve tank is not holding pressure. (I used a gowesty bike pump) Prior to reading the article I didn't understand why the pressure containment valve was so important and dumbly thought I was good since my cap wasn't leaking at the threads. Now I see that my pressure containment valve has basically been busted for god knows how long, allowing coolant to boil at a much lower temperature than it should be and possibly not cooling the engine properly. I have no idea how long my cap has been busted because it's the first time I've tested it. Only after reading the article do I think I understand the potential consequences. My cooling system otherwise appears to be functioning... So the question is what kind of damage to folks think I did? I replaced the head gaskets 2 years ago and am wondering if my faulty cap could have been the cause. Really hoping I have not been destroying my new heads + gaskets with this bad cap!

Sun Jul 05, 2020 5:17 pm

I realize there is a lot on this topic and just found these two threads which are interesting in case others are wondering, apparently some argue that it's ok to drive on a cooling system that is not pressurized. Can someone explain this logic to me?

Here's the posts discussing drilling a hole in the cap, keeping the cap loose or otherwise not having pressure in the system. This seems dangerous to me if I understand the way the pressurized cooling system works correctly?
https://www.thesamba.com/vw/forum/viewtopic.php?p=8273866
https://www.thesamba.com/vw/forum/viewtopic.php?p=7016593

Sun Jul 05, 2020 6:37 pm

at this point, worrying about possible damage is fruitless because it does not warrant a tear down to inspect as you are not seeing any symptoms. just go onward.... get a good cap, add some Redline Water Wetter (also reduces micro-boiling in addition to proper pressure), and carry on with new knowledge.

i'm on the same page as Chris with respect to the importance of system pressure... it's not just about boil-overs but there's deeper science with respect to hot spot control. between the dang Blau caps being so tempermental and the poor quality of replacement plastic pressure tanks, it makes the Rocky Mountain Westy 'the Tank' attractive even with the price tag. take a gander at some gorgeous Industrial Art.

https://www.thesamba.com/vw/forum/viewtopic.php?t=728917&highlight=

Sun Jul 05, 2020 8:10 pm

DanHoug wrote: even with the price tag

and that's where we are at driving this old junk...either pony up for something custom made that works, or keep chasing issues with junk aftermarket parts. it's sad, really... but on the flip side it's nice to know people are coming up with stuff to keep these on the road.

victor reinz is garbage these days, elring is getting there...conti has been slipping in quality as well. it sucks.

Sun Jul 05, 2020 8:28 pm

After my 4th blau cap (latest one was purchased new old stock from Europe) I finally took delivery of RMW the Tank this week. Ironically when the tank was initially introduced I recall scoffing at the pricing and thinking to myself who in the world would spend money on that. Fast forward several years, several cracked coolant tanks, several weeping level sensors and many caps - here i am, money well spent.

Sun Jul 05, 2020 10:00 pm

i spent a lot of money upgrading cooling system parts. in the end, head gasket leak was the problem. fwiw, i am running a plastic tank with a blue cap, with no issues. yes, they need to be replaced every 10 years, but meh.

Sun Jul 05, 2020 10:19 pm

There has got to be an existing expansion tank out there that can be adopted to fit this application, especially one with a standard old school bayonet type cap. The golf ball tanks on most '90's and later VAG products should easily be adaptable to a van. The Mk4 tank on my TDI swap works excellent, and the level sensor is perfectly compatible. $250 for an expansion tank is bafflingly absurd as the sole option out there to replace these aging tank designs. If I still had a WBX van, I'd surely invest a few bucks into investigating other more affordable options

Mon Jul 06, 2020 7:05 am

new expansion tank caps are available @ the dealership.
i use OG tanks & caps on my vans. never a problem.

if my method becomes outdated, i would convert to the later ball style tank & cap that can be found by the hundreds @ scrapyards.