I have a 2.25 petrol 1983 series 3, its been in garage for a few years having alsorts of work done, engine rebuild welding ect, i have fitted a new rad and flushed out system, problem is after 5 mins of running there is a lot of pressure it top hose, which suggests to me head gasket, new one fitted when head was converted,
if i run it with out rad cap off, system warms up normally stat opens and fan cuts in no probs (kenlowe fan) refit rad cap once warmed up and leave running all ok no excess pressure all is fine, leave to cool down and top hose sucks in, as if there is a vacuum in system,
would i be right in thinking rad cap is at fault (although its new and came with rad).. its the type with a expansion bottle on the N/S of rad,,
any thoughts would be very helpful,,

Thanks

try it without cap ,sounds like cap isnt letting excess pressure out or blockage in pipe