Overheating coolant steams & bubbles

Re 1977 xj6c with a chevy v8 350. Overheating, smoke out of overflow tank. Thought it was a blown head gasket. Now noticed that the radiator fan is not working–cool or hot coolant. Make sense? When driven, the temp seems to dip a bit. When parked in the garage, temp goes up & eventually . . . steam. Which fuse controls the fan? Any help welcome. Lawrence from upper New Hampshire, USA.

HI Laurence Welcome to JL.
You might have better luck posting in the Lumps Forum as yours has a V8 conversion.

All engine will overheat without fan working, Lawrence - and while driving; ram air flow will cool the engine…

However, there may be more to it than just a failed fan. Insufficient coolant will cause overheating - and steam means coolant is forced out of the engine. Have you checked coolant levels?

Also; ‘smoke’ from the overflow tank implies that exhaust gasses are entering the cooling jacket - which indeed may imply a leaking head gasket. A compression test is called for…

Basically, system pressure should prevent boiling until coolant temp reaches some 120C (250F). If the system is leaking, pressure will be at ambient - and the coolant will boil at the boiling point of water. Did you notice the temp when the engine boiled?

However, the cooling set-up on the Chevy may differ more than marginally from the Jaguar - so Robin’s advice is very pertinent; consult the lumps forum…

xj6 85 Sov Europe (UK/NZ)