yes and no, it could be the inlet manifold gasket, i would change that first along with new coolant and try it

 

Thanks for that, I'll give it a shot. Further investigation showed the cooling fan wasn't working but the dash temp never went above 'normal'. See how it goes with Inlet Manifold replacement.

 

it was forcing coolant out of the coolant reservoir as it pulled back into the garage.

Hi Andy. Was the coolant escaping from the cap or elsewhere on the tank?

 

Hello LeRich - it was only forcing it's way past the reservoir cap, no visible leaks anywhere else in the cooling system.

 

there was a lot of 'lively' pressure inside the reservoir - on tentatively unscrewing the cap slightly, more coolant was forced out

 

Not HGF for certain would think, but it certainly doesn't sound good - it could possibly just be an air lock or some other blockage in the coolant system causing overheating/boiling (having been stood for a lengthy period, a stuck thermostat is a possibility), but to me it does sound rather like leakage of exhaust gases into the coolant past the head gasket. If so you are likely to have significant residual pressure in the system when it has completely cooled, and/or may find a significant amount of coolant disappears too (when cold, take each of the spark plugs out and check for any signs of coolant in the cylinders).

A 'sniff test' with an exhaust gas analyser can aid a positive diagnosis of fire ring HGF, but as there is always some hydrocarbon contamination in the coolant, it can't be used to discount the possibility altogether.