A guy I used to work with has a beautiful 66 tbird/390...rebuilt the motor(think it was using oil) last year, now its overheating. he pulled the motor back out again, said the guy that built it had too tight ring gap/friction overheating(but I kinda think if it had been tight it would have seized/galled the bores/etc...), anyways- put back in, overheating, pulled back out, replaced head gaskets thinking one may have been installed wrong or something, overheating still...two water pumps, triple core radiator etc...still overheating.
I just saw him two days ago and he told me what he'd done, and how much he'd spent(first time I'd talked to him since last year before he tore it down). He said that it dont overheat driving or cruising on the highway, but as soon as he slows down, it heats up- heavy radiator added, 7 blade fan added, still heating up. he said someone told him he had the wrong heads~castings were no good(original parts), I told him I couldnt see how heads could overheat at idle/but not at cruising speed...sounded like water pump/fan/radiator issue to me, but hes replaced all these things twice already. he started it up for me and within 30 seconds the temp was pegging out...maybe some kinda air 'bubble' trapped in the water jackets?
I really doubted a cracked block/head, or 'wrong heads' as his buddy told him could result in overheating at idle but not at cruise rpm- would hate to see him throw more money in the wrong direction...it sure sounds like its not pumping enough water to me- cant imagine radiator contents heating that rapidly at idle...sure sounds to me like his pump aint moving any coolant at idle- suggested he leave cap off to prevent pressure and put some clear tubing on one of his radiator hoses to *maybe* see if anything flowing. something else- he has looped the heater hoses as his heater core started leaking- that couldnt bypass enough at idle to starve a head or something could it?
Anyone got any ideas or heard of any such thing before? Really a shame as this car is a cherry original, perfect everywhere except for this overheating thing. that car has the coolest red leather interior ive ever seen...anyone thats got any advice please share and I'll pass it along.
if you think it might have an air bubble in addtion to raising the car up as suggested you might try an old racers trick. take your thermostat and drill a 1/8" hole in the outer edge of it. that will allow the air to excape when it's cold and closed. make sure the hole is at the top. it will also allow a very small amount of water to be circulating all the time. may or maynot help but couldn't hurt.