v6 overheating

My '67 is overheating here on the first warm days of the year. PO put in new radiator (no leaks, even heat across fins), water pump, hoses (both heat up, so water curculating to engine), I put in new thermostat (190). Ran in cool weather 3/4 up on temp gauge, but first day over 70 and she boiled over.

I'm changing the thermostat to a 160. No fan shroud, but at constatnt 45 to 50 mph, it doesn't cool down, suggesting its not an air flow problem.

I don't like uglier answers: head gasket, cracked head, cracked block.

Other idaas?

Wayne

 

I'd like you to define the statement above.
Boilover is occuring after you shut the engine off ?
Boilover occurs while driving ?
Keep in mind that if you are filling the radiator to the very bottom (or top) of the cap neck, heat absorbed after shutdown will expand the coolant, causing it to push out the overflow tube/hose. This would be considered noraml; This is why closed systems after a tank to catch the coolant.
The coolant will not push out the overflow tube/hose if you fill to about 1 inch below the cap neck; you are leaving room for expansion of the coolant.

other than that, all the usual checks and rechecks apply:
temp gauge
thermostat
water pump
cap pressure test
fan belt tension
leaks
etc etc

 

silly question probably but is the thermostat installed correctly?

How far is the fan away from the radiator?

 

"boiling over" meant steam pouring out of front grill.

I replaced the thermostat with a 160, everything checked out, normal circulation. Drove for 20 minutes and didn't overheat. Fingers crossed.

However, my temp gauge has now become flaky, going from low normal reading to hot reading in 30 seconds and then a few minutes later back down. I don't believe the engine is overheating.

Should I replace it with stock gauge or after market?

 

Could be the sender causing that problem as well.