Hi Art. I think others have it right, likely quite normal after a good run. Starting from a cold/warm engine with the rad cap off and seeing if it suddenly rises and bubbles within 5-10 mins as soon as the thermostat starts to open is more definitive of a head gasket leak into the water jacket -I was quite impressed the first time I witnessed that.

In my 940T, between the hotter engine environment with a turbo, a plastic sided radiator, failure prone heater valves and failure prone heater cores that are an absolutely bear to replace, at the first opportunity I changed from the stock 700/900 green (21 psi) cap to the lower pressure 240 black (11 psi) cap. I believe at one point there was a white (15? psi) cap used with some early 740s that has been NLA for years, also a grey (21? psi) cap. For my 940 NA I decided to live dangerously and keep the green cap, but wouldn’t you know it, that was the first of these ‘95 cousins to have a cooling system failure. If I ever trip over a free black cap I’ll likely switch it too.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now