i have a 1995 monte carlo z34 with the 3.4 dohc motor. i bought the car with a blown head gaket and have put 2 new heads and gaskets the works (i work on cars for a living and this one is stumping me). if i leave the t stat out no problems but very little heat. when i put the t stat in it will warm up to half way as long as ur not driving it will stay half way. the fans work and i have heat so water pump is working. when u start driving it goes up to almost 260 but does not act like its running hot. and is not boiling when i stop. when i stop and leave it running it will cool back down to half. any help would be great. thanks guys

 

it has a new tstat and have drilled a small hole to help bleeding process and have all air out of system burped with yellow bucket.