my 79 brat has had some really weird cooling problems... my rad has been leaking a little bit... out a hose it seemed... so i tightened it... seemed to fix it... still might leak a tiny bit...

 

 

 

 

so i topped up the radiator and continued...

 

 

 

my car has an aftermarket overflow on it... and it was empty... so i put a smidge of water into the overflow so it wouldn't run low again... even with the rad completely full i've NEVER had any fluid go into the overflow...

 

but after driving it for a day or so the overflow was filled to the brim and was squirting fluid all over the engine bay... and of course... the rad was near empty...

 

the fluid wouldn't go back into the rad so i had to drain it back in... i've been doing this for a while now, overflowing then pouring it back into the rad...

 

the car works better when no fluid is in the overflow it seems... but even if the rad isn't completely full itself... now it does over heat... if i drive it hard (like i almost always do) it will overheat...

 

 

 

my fan is hard wired on... so what might this be? thermostat? radcap?

I'm not entirely certain on cooling systems, but if the radiator was boiling over, doesn't that mean the thermostat is at least opening ok?

I'd say toss the overflow for a while and see how that affects things:confused:

Sorry I can't be of much help....

Interested to see how this turns out, Goodluck!

does it over heat before or after the overflow starts filling? if it's after then it's your radiator cap letting the fluid through too early (right?)

 

also I'd replace the thermistat anyway, it couldn't hurt anything and could get you a little performance if you find a lower temp one