I have an 89 Firebird TBI with a 305. Recently my radiator exploded (in the most literal of senses, it had rust and those parts gave way) And so I swapped with a radiator out of a Camaro at a pick-a-part. The radiator was in AMAZING condition for being a junkyard part. I installed it, and at first the temp gauge would surge from hot then back to cool, then stayed steady for the rest of my drive. But in my haste, I forgot to tighten one of the hoses, and the pressure kicked it off. So I re-attached the hose, and since my temp guage has been surging, my car overheated today, and when I looked, all my coolant ended up in my resiviour tank. There's no leaks or anything, when the car was shut off, it slowly began to funnel back into the radiator, but when the car is back on...the resiviour tank fills back up with coolant. And I mean WAY past the -full- mark. Why is it doing this, anyone know?

 

how long does it take to over heat? does it run at a certain temperature and then overheat after 20 or so minutes of driving? i'm having a similar problem with my built motor.. its been a pain in the ***.. i either have a faulty brand new water pump or a tiny head gasket leak.

make sure the rust and stuff didnt destroy your thermostat. i would go ahead and replace that. also make sure you purged all the air out of your system too. leave the cap off the radiator and let it idle at a low low idle.. 700 rpms or less. by the time your top radiator hose is TOO hott too touch, the air will be out of the system. you will see air bubbles in the radiator and they will eventually go away.. do not rev the engine or it will vaccuum the air right back in. Air in the system can trap in your pump and not let it pump coolant so try that and a thermostat because spending more than $10.

 

Yea, it's after about 10 minutes or so. It'll stop around 220 or so sit there for a few minutes, slowly build up to the 3/4 mark on the thermostat, then shoot past 260, drop back down, and do it again and when most of the coolant ends up in the overflow tank, the car stays overheated and I have to pull over.

I'll try what you've suggested though, see if that helps or not---

 

I would replace the thermostat and the radiator cap both. If your vehicle has a heater return hose just below the fill neck, I would run it until the top hose gets hot (don't fill it clear to the top or alot of fluid will push out as the thermostat tries to first open) then, if you have the wherewithall, clamp off the heater hose and then hold the rpm up and top off the radiator, while still holding the rpm up, get the cap on quickly, release the clamp on the heater hose, then let the rpm go to idle. If full, you should have good heat inside the car at idle. Now go ahead and fill the reservoir to the full mark. If you do not have a heater return, disregard clamping the hose off..