Ok, this isn't for my fbody, but rather my parents jeep grand charokee. Recently the radiator started leaking from the side tanks. And overheated just a little (loss of water), not sure since i wasn't there, my dad told me about it. so i replaced the radiator tonight and flushed the cooling system. And while its holding coolent now, i noticed that it takes only about 2-3 minutes once u start driving to heat up to about 200*, right about where the thermostat opens. but even more amazing, is that it cools down to about 170-80 or somewhere around there very very quickly.. you can watch the guage drop almost as quickly as an oil pressure guage. its just weird how quickly it cools, and then heats right back up to 200 again. The cycle only seems to take about one minute when driving. What would be causing it to heat up so very quickly, but when the thermostat opens it cools down very quickly. could it possibly be that when it overheated it cracked the block? or maybe its running lean? the temp never gets over 210*.. but its how quickly it heats and cools off..

 

could it be the themostat can't handle the pressure anymore???

anyone

 

Did you burp the system? Could be air pockets in there not allowing the water to flow correctly. Is the stat new? Does the fan come on when the car is off? When the temp drops is the car still running or is then when its shut off?

 

how does one burp the system? i just ran the car with the heat on while filling the rad, is the correct?

 

for the most part i filled it with the hose and a t-connection on the heater hose, and then filled the rest in the radiator, and i saw it push out a few bubbles to the overflow, and then i rechecked it today, and it was all full..

the thermostate wasn't changed, and the fan is mechanical..