Pressure cap, low pressure

[Wildthings]

I was wondering if there is a replacement pressure cap available with a lower pressure setting than the stock cap? With all the old parts that make up the cooling system on these vans, I would think that lowering the pressure in the system might save a breakdown or two.

I run 4 psi caps on my other older vehicles and have been happy with the results. Don't live in a particularly hot area and only see a couple of weeks in the nineties or above most years.