"The upper radiator hose is warm to touch and the coolant overflow tank is overflowing with coolant; about a quart of coolant is lost each time."

Does this mean that you lose a quart of coolant out of the pressure release pinhole in the top of the reservoir cap? Otherwise, where is the quart of coolant going everytime you run the engine?

Assuming it is all coming out of the reservoir cap, that is a lot of fluid to be pushed out. Maybe you have air traped in the system. This would cause inefficient cooling and gases expand a lot more than fluids, so as the car temp rises the volume of the air in the system rises, as well as the pressure, and pushes out the fluid in the reservoir. When you intstalled the thermostat, did you make sure you had the bleeder valve installed in the 12o'clock position and that you installed in in the proper direction? This allows trapped air to escape the system.

Does the engine run well otherwise? There might be anoher reason that the engine is burning hot, like an excessively lean condition caused by a vacuum leak. You might want to check the O2 sensor with a voltmeter to make sure the engine is running at correct mixture. Also, you should check and maybe replace the hoses that run from the engine back to the heater core for leaks of anysort. If you only get cool air out of your heater then either the car isn't warmed up, or there is a clog somewhere in the system.

I had a similar problem with my car. One day it decided to overheat for about a minute after warming up almost every time I started it. I replaced everything in the cooling system, except for the water pump, and flushed everything. After going through all of that I went back and replaced the thermostat again, but this time with one from the dealership, and it was rated the lowest temp I had found. After installing it I warmed up the enigne with the reservoir cap off. When the engine started to get up to temp fluid started to flow out of the reservoir but stopped after 10 seconds or so. I think this was due to the system purging the air. Then no more problems. A few weeks ago I was even in 110 degree heat going up 10% grade without a single problem. Maybe you just got a faulty thermostat like I did.

Check this entry in the FAQ as well as other entries in this section. It may be you have a leaking head gasket.

http://www.brickboard.com/FAQ/700-900/EngineMechanical.htm#TempGaugeActsOddlyLeakingHeadgasket

Did you back flush the radiator fins ? Take a garden hose and spay through the fins of the radiator from the engine side towards the front. Take the grill off, and look through the radiator...if you can't see anything.... flush .

All fins are straight and not bent or mushed together ?

The "Beck Arnely" thermostat...had the little jiggle pin (looks like a small rivet on the plate of the thermostat......(ensures proper bleeding of the system), and was the thermostat put in properly ? I believe the top cross bar is to run from 12:00 - 6:00 and the jiggle pin is to be towards the front of the car.

Hope this helps.

This sounds like the classic temp sender problem. the sender is located under the #2 port of the intake manifold. Remove the lead and ground it. the temperature should go hot. I did mine last year and all my temp problems are gone. You may have to loosen the intake manifold to get a socket on it. Its a nice cheap fix that is the most likely problem.
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Simon 80 240 299k 17 years. "White Lightning"

When the temperature gauge needle falls, it stays steady just below the left tip of the "N" on the temperature gauge.