94' LT1....no major problems. I run it through traffic in a Fresno, CA 115 degree heat wave and 5 minutes after she's parked, boiling anti-freeze spills out on the driveway. okay, the original owner i bought it from filled the thing with water (idiot), and now i've put almost a full jug of 50/50 anti-freeze. I start the car, warm it up, and take it for a spin around the block. seems fine, then overflows again. I repeat the process; fill her up, warm up, no driving around the block. I check the level and i can't even see anything, i had to use the rest of the anti-freeze just to fill up. what's the catch to this??

 

check you r oil, if it looks like a chocolate milkshake, then it is time to pull the heads

 

Make sure you have a good thermostat and radiator cap in the car. Then fill and bleed the cooling system with the bleeder screws. AND check to make sure you don't have a milkshake in the oil.
I also run waterwetter in the antifreeze to help keep it cool. I also had MadZ28 provide a custom tune and turn the fans on at 175 instead of the factory 220+
Have you back flushed the radiator? If it is plugged up, it won't cool the car.

 

I had a similar issue on my '96 and a new radiator cap cleared it right up. Also, make sure you get all the air out of the system.

 

Besides what has already mentioned, you will be surprised how many checks it will take to get the coolant system stable after an upsetting.

I had the whole system drained, water pump replaced, new thermostat install, new hoses and it took almost a week of driving cycles and "topping off" before the coolant system finally stayed full.

Hint: run the heater a few times to get the flow through there and air bubbles pushed out.

 

So if the original owner filled it with water and you've only added a gallon of 50/50, your at best 25% coolant.

Bleeding all the air out of your system is key.

 

I think you want to run only water for best cooling performance right? Just water-wetter/straight water, and distilled if possible, if I remember correctly. Although the anti-freeze does have some anti-corrosion properties and such as well......

 

I think that gives me something to work with ....now that I'm back into school 2 days a week starting tues. I will have zero time to screw around with the car...crap. I'll just have to take a day off work to settle down with this issue. Most of it can be pulled off in a quick minute or two, but knowing me, i'll want to get the majority of troubleshooting out of the way in one shot.

Thanks a lot for the input. Makes things really easy.