engine boiled no visible water leak is this a head gasket problem?

Or an air pocket, you may need to bleed the cooling system to get rid of any air in there. Open the bleed screw on top right of radiator and fill up the coolant, usually air pockets occur in the top half of the radiator.

 

Also try changing the radiator cap ... They usually crap out very quick ... Iv Had to change mine twice this year , the last time my car did what yours has done ... It boiled and temp guage went crazy but still had coolant in the system , I bled the system added a bit more coolant and changed the cap and it hasn't done it again ...also check the claps on all the hoses as they won't show signs off leaking but under pressure they can leak just enuff to cause the car to overheat

 

Probably air pocket due to lost coolant caused by a leak. leak maybe only under pressure, split radiator tank, leaking thermostat housing (Back of engine leaks onto bell-housing) water-pump all common places fo a vz to leak. get a pressure test



From an earlier post of mine:
vz's run hot 95 to 105 approx deg. water boils at 100 deg so if your cooling system cant pressurize (Has leaks) it will boil at normal temp. Water under pressure raises boiling temp. While the temp gauge is normal at 25% it can be boiling at 30%. Change the radiator cap, look for leaks from thermostat housing gasket, its in the middle of the v at the back of the motor in a s**t of a place. water pumps leak as does the alloy radiator feed pipe above it, Radiators split the tanks.heater taps leak. Its not unusual for you to fix one thing and then it start to leak from some where else. proper pressure test is a good idea. Coolant around the trans is normally thermostat housing gasket.

 

. Yup exactly what he said .... I had radiator blow so I fixed that ... Then water pump started leaking , fixed that ... Then had coolant all over bell housing but that was from the radiator feed pipe and it created a pool then dripped backwards making it look like the thermostat housing , has to o rings in it ones a weird shape , fixed that ... Then both hoses on the heater tap have original clamps on them that started leaking so fixed that .... I'm still waiting for the thermostat housing to give out ... BIG FUNNNN !!!!

 

Thermostat housing is not as big a job as some think. It's fairly easy to do with a 1/4 inch set and some ratchet spanners. Can be done from above engine too

 

a mechanic tried to charge me $600 to pull gearbox out to fix the housing coz he reckons it was leaking when I ended up figuring out it was leaking from the radiator pipe coming out of the block and dripping backwards ...best $600 I ever saved hehe