Hello, i have a 1999 Seville that steam starts coming out of the coolant recovery tank cap, i took out the thermostat replaced the water pump with a used one from a yunk yard, flushed the radiator and still overheats, once it gets to normal temperature it starts steaming out of the cap, after a while coolant starts coming out of the cap, and then the temp. starts rising. Help please.

 

Sometimes the Thermostat can get stuck shut, but if u took it out already, you don't want to everheat these motors to much, and once can be too much, some will argue that without a thermosat the engine would overheat also because of the lack of backpreasure on the cooling system, the flow rate is too high without the thermostat and you don't get correct heat exchange through the radiator, I for one don't buy into that soo...

Worse case you have a bad cylinder head gasket which is what its sounding like, how the engine running otherwise? Any smell of anyfreeze from the exhaust? Rough Idel, Low power?

 

I have heard many reasons pple take out the thermostat and it usually is because it is a TEMP fix. i would use a thermostat especialy if you do alot of in town driving. Also it will cause your car to stay in open loop causing more fuel consumption. I did this on a car of mine and noticed if i drove on the highway the car wouldnt get warmed up and would use more gas unless i drove in the city and if the temp was higher than 70*F it would run alot warmer than normal. What Dalamak was stating is actually almost true. What happens is that the coolant doesnt stay in the radiator long enough to disapate the heat causing the coolant temp to be hotter than normal operating specs thus causing some cars to overheat if the car is being driven hard or in harsh environments (hot temp outside, racing, towing, going through hills or mountains,etc.) check oil to make sure there is no coolant in your oil it will look foamy or milky on the dip stick. Also does the car smoke when first started up then goes away? (this may be hard to tell since it is winter) Try to smell the exhaust as well to see if it smells like "maple" which can be a sign of coolant geting into the cylinders.
good luck and try to give us more info.