The car was leaking antifreeze and started smoking in 40 degree weather. I filled it and it stopped leaking, but the engine is still overheating. If its the water pump, how can I replace it on a 1992 chevy caprice?

natural for engine temp to rise in Traffic - Until Themostat opens ) cooling fan sensor kicks on fan . But Antifreeze is not just a Cold weather item . Coolant is Absolutely Necessary for Hot Days . You must be full to recovery bottle setting of cold when checked prior to start up . Coolant for your make / model is Reddish - Pink colour and should have a reading of -25 thats negative 25 degrees the Lower the Better even - 50 .. Why ?? - 50 is 50 %% antifreeze / Coolant Concentrate MIX Gives Hot weather cooling Ability or very cold weather starting / winter HEAT .

You have a head gasket problem with the engine generating abnormal pressure, and sending all the antifreeze to the reservoir, thereby leaving the engine running dry; it is dangerous for the water pump to operate with no water.
Drill 3 11/64 or 3/16" holes in the thermostat side facing the engine, making sure not to touch the opening mechanism; this will keep antifreeze always running thereby, compensating for the abnormal pressure regenated by head gasket leak(s).
Your thermostat was never your problem.
In cold weather, 5 degress celsius or under, the thermostat takes longer to open and more antifreeze will be sent to the reservoir leading to an overheating.. Partially cover the radiator with a sheet metal piece to make the thermostat open faster and stay open, as the antifreeze is not being cold that much by cold air. You're fooling the cooling system into warm weather driving.
Don't waste your money buying radiator stop leak or liquids to repair head gaskets; this will only corrode and make your radiator to eventually leak.

a flashing check engine light (CEL) is a warning to stop driving-one that is on steady (not blinking) means something is wrong, but blinking is BAD-make sure it is completely cooled down, and fill the overflow/surge tank, start it up (use 50/50 antifreeze) and let it idle until the engine temp is all the way up-this can take 10-15 minutes, make sure the heater is on high temp setting and the fan is on-look at the temp gauge if it has one to see if it looks normal. If all looks good, fill the tank to the FULL mark (or a hair above it) and put the tank cap on tight. Drive the car for about 10 minutes, and pay attention to the temp gauge-if it looks good, and the engine is alright, the CEL probably with either not light or will go off by itself.

It is possible you did damage driving it with a flashing CEL, however-if so look for leaks, smoke out of the exhaust, poor running/performance, or more ominous signs of trouble like air bubbles in the overflow tank, oil in the antifreeze of antifreeze in the oil-aluminum engines do NOT tolerate overheating, if you ever see a high temp gauge and/or a flashing CEL-STOP and get it checked out, you will save yourself a lot of money being prudent.

Could be a lot of things. First check for leaks. Fill the system. If you have a radiator cap, take it off and make sure the radiator is full--not just the reservoir. Start the car and let it idle in park with the cap off until the car is warm--keep the radiator full. Then put the cap back on and watch for leaks. Let us know what you find. I have more tips at http://www.fixya.com/cars/r5929960-s_thermostat . Let me know if you have questions.

White smoke out of the tail pipe especially on '''warm''' weather usually means antifreeze/coolant leaking in to the cilynders. you may have a blown head gasket(cheapest to replace) and or a crack/warped cilynder head or crack block(not cheap) if the smoke its happening in '''Cold''' weather it could simply be condensation which is normal.

To find out exactly ,in a v6 engine ,simply take out the 2 middle spark plug (1 of each side) and crank the engine. If you see white smoke come out of either one thats where your leak is and you would go from there.

Note:

Just crank the engine '''Do NOT''' let the engine run for long without sparkplugs or catalyc converter damage may occur.in a 4 cilynder engine take out any center spark plug and see where the leak is

Your van is 11 years old and it is time for a cooling system service. Drain the radiator and flush the cooling system. Replace the thermostat in the engine and fill the radiator with a 50/50 mix of antifreeze and distilled water. Make sure to clean the front cooling coils of the radiator and remove all bugs and debris. Make sure the cooling fans are running as they should. Anytime the A/C is on the fan should run continuously. Caution: If you have been loosing coolant with no apparent leak then you may have a blown head gasket. You might also see white smoke from the exhaust if the gasket is blown. This requires the heads be removed and new gaskets installed.

Replace the thermostat.

two places to check.... the water pump or one of the frost plugs has failed. what colour is the exhaust smoke ?

the other problems could be from the engine overheating so much

You have a coolant leak most likely in the heater core. Try disconnecting your heater hoses and coupling them together, then running the engine to see if the leak goes away. If it does, I would have the heater core replaced.

your radidator hose on the left side has a hole in it and when it gets warm it leaks out. i would replace the hose.