Hello fine folks,

I am very happy to see such a community in existence on the net!

I have a problem, as some other seem to as well. Only thing is, it happened suddenly.

I bought an '83 300sd from charity auction (pix below). She is so nice, but the first few days I drove her, it seemed like she was losing water from an unknown cause, but was not leaking. I put some bar's leaks pellet sealer in and things seemed to be normal for a month or so. (80 deg. Celcius, constant.)

Just 2 days ago, I had to turn the AC on, driving back from a 50 mile trip. It was hot, and although I knew my compressor was bad and noisy, it still worked, so I used it. Figured it would give out and I'd buy a new one. I drove for 30 miles, no problem. But as I got to the toll booth, I shut the AC off, and the temp. instantly shot up to 110, 120. Perhaps there was too much stress on the motor with that impaired compressor.

Long story short, I replaced the lost water, and bled the system. I even tore off the ac belt, thinking maybe the compressor had seized. Now, The car will drive fine for more than 50 miles on the highway at 60mph as long as it has fresh water in it and you don't stop. But once you stop, the temp. shoots up and won't come back down unless you turn the heater on. Even then, it is not within normal operating temperature. There are no leaks from anywhere, just pressure building up and water spraying out of the pressue valve on the expansion tank cap, slowly. The water stops coming out when the car is turned off. I have bled the system, following the procedure to plug the small return hose from the reservoir, and then squeeze the top rad. hose, to fill the bottom one. Seemed to be the fix, but then I found that it still overheats after 30 or so miles on the highway.

Could this be a thermostat? Clogged Radiator? It's strange because it has been overheating ever since that day I turned the AC on for 10 minutes. In fact, I had turned the AC on before, just not in such hot weather. (90+ degrees)

I am about to change the thermostat, cap, and possibly the pump. I am hoping you guys may be able to shed some light on the matter. It would truly be a blessing, as this is my only car and I need it to get to work every day. I am mechanically competent, and can do anything basic to semi-expert to a car. Any suggestions?

THANKS A MILLION!

-Rod R.