VW expansion tank

I've started this thread as although it's been raised on the "Hose Reliability" thread it's wandered a bit and doesn't really sit there.

I'm looking to use the VW tank (if poss) and have been looking at the pros and cons on various forums, my biggest concern is that it's recommended to use the blue cap which is rated at 1.5 bar. The TF cap is currently 1 bar so I'm concerned that I'm asking an old system to take a possible 50% increase in pressure, I've tried looking on line for a 1 bar cap with no luck so far.
Does anyone know of a 1 bar cap that fits this VW tank or are my concerns unfounded?

Your concerns on the pressure cap blowoff values mirrors my worries when I fitted mine several years ago & like you I tried to ascertain what I was letting myself in for if there was a problem.
It sounds like you have approached the research with more tenacity than I, however the outcome has been the same; neither of us know the answer.
I chose to chance it & up to press it hasn’t been a problem.
My car is a 98 Mk1 & most of the pipe work is original, the replaced bits are associated with the fitting of a PRT.
Firstly I fitted it at the front under the spare wheel well, but I wasn’t happy with that, this involved cutting the radiator top & bottom hoses & mounting the PRT on a cross pipe. This was removed & with fresh pipes on the rad’, moved it to the rear of the car as per later tf’s. When I say fresh I mean second hand, removed from a known car.
The upshot of this is I’m flying by the seat of my pants with a pressure cap rated at 50% up on recommended, the oldest pipes fitted are as built & the most recent pipes only a few years younger. The original mild steel rad’ pipes are now stainless & I have a dual digital thermometer fitted, one sensor on the send & one on return. I also have cooling fan monitoring, override switches & am playing with pressure monitoring.
Most of this trickery is totally unnecessary but I have the skills, the knowledge, the time & a budget.
Many of my ideas have morphed into designs & moved away from their original purposes to find homes elsewhere.
Happy days & I realise you’re little further forward but you have a fellow traveler with me & if I have any problems in the future I’ll post on here, as I suspect you will. Mike.