1996 caprice do not have radiator cap

Yes, it does have a radiator cap. Usually on the passenger (right side), side of the vehicle near the radiator.

Check the oil dip stick if it is a milky white this is really bad being cracked engine head or blown head gasket.
More than likely and best out come it will be the radiator or a radiator hose.
If you can see water stain some where around the radiator it does not need to be a big amount.
Or a radiator hose that may have water around it or coming out when hot then that is your leak.
Maybe a good idea to take to a radiator place or a mechanic ask them to put a pressure test on the radiator.
Also only fill radiator when cold or if you need to do when hot make shore the car is running to avoid cracking the engine head as this will make any grown person cry $$$$
And do on a hill with engine facing up running and cap off little bubbles will come out keep filling when bubbles stop put cap on fill reservoir ( a little container next to the radiator).
Let me know if this helps.
Regards Craig

1. Step 1 Drive your Ford Taurus up a set of ramps onto a pair of jack stands, if it is a 1996 model or newer. Remove the lower splash shields. For 1986 through 1995 models, you can remove all necessary components from above.
   
2. Step 2 Begin by disconnecting the negative battery terminal and draining the radiator into a transportable container. Open the plastic draincock on the lower rear of the radiator and crack the radiator cap.
   
3. Step 3 Remove the overflow tube from the coolant recovery bottle and disconnect it from the radiator. On SHO model engines, remove the recovery bottle as well. Next unscrew the shroud and remove it from the retaining clips. Disconnect the wires to the fan motor, and remove the fan assembly and shroud in one piece.
   
4. Step 4 Squeeze the hose clamp ends together on the radiator side, and remove the upper and lower hoses. For automatic transaxle models, use either the custom Ford disconnect tool T82L-9500-AH or two crescent wrenches to remove the transmission coolant lines.
   
5. Step 5 Disconnect the radiator supports. 1986 through 1992 models will have two upper retaining screws for 3.0 liter and SHO engines. 3.8 liter engines will have two driver's side hex nuts and two passenger side screws. All other models have either the upper screws or the combination of right hand hex nuts and left hand screws.
   
6. Step 6 Tilt the radiator backwards toward the engine and lift it out. Fit the new radiator into the support and replace the support screws and nuts. Reattach the hoses and wires in reverse order.
   
7. Step 7 Flush the new radiator with either water or a commercial flush treatment. Connect your battery terminals and replace the coolant and let the engine idle for 5 to 10 minutes with the heater on and the radiator cap removed. Top off the coolant as necessary.
   

Thank you,
Lee

answer found here:
http://www.ehow.com/how_4506379_replace-radiator-ford-taurus.html

DO this when the car is cold,not driven,remove Cap From Radiator and add Coolant.when filled,replace Cap,Run the Car for Five mins.Then Fill the Resorvor,There is a mark on the side Where to Fill To.OK...

If you fill up the coolant container it will get into the radiator if it is low. If your radiator is completely empty remove the highest hose on the engine and fill through the top of the motor. Otherwise the coolant container is the only place to add coolant. Hope that helps!

check the radiator. maybe you punctured it.

make sure the engine is cold, if you try to open the radiator cap while engine is hot you can get badly burned. get a container of coolant mixed with water, should be 50/50 mix. first open the radiator cap, which is at front of engine compartment near the center. roundish cap with 2 wings on sides. turn counterclockwise while pressing down to release cap. then fill to top with coolant mix. replace cap, turning clockwise till tight. then follow the small rubber hose from radiator cap area to the coolant resevoir. this container doesn't need to be filled completely, it has a full line. fill to that.

Yes. Flushing the radiator would be a great first step. Check that your heater core feed and return hoses are not leaking or clogged. If it is still acting up, you may have a clogged or leaking heater core. Good Luck.

Instructions Things You'll Need:

• Ramps and jack stands
• Phillips and flat head screwdrivers
• Container for used coolant
• Crescent wrenches or Ford disconnect tool T82L-9500-AH
• Hex nut screwdrivers
• New radiator
• Flush treatment
• Coolant

1. Step 1 Drive your Ford Taurus up a set of ramps onto a pair of jack stands, if it is a 1996 model or newer. Remove the lower splash shields. For 1986 through 1995 models, you can remove all necessary components from above.
   
2. Step 2 Begin by disconnecting the negative battery terminal and draining the radiator into a transportable container. Open the plastic draincock on the lower rear of the radiator and crack the radiator cap.
   
3. Step 3 Remove the overflow tube from the coolant recovery bottle and disconnect it from the radiator. On SHO model engines, remove the recovery bottle as well. Next unscrew the shroud and remove it from the retaining clips. Disconnect the wires to the fan motor, and remove the fan assembly and shroud in one piece.
   
4. Step 4 Squeeze the hose clamp ends together on the radiator side, and remove the upper and lower hoses. For automatic transaxle models, use either the custom Ford disconnect tool T82L-9500-AH or two crescent wrenches to remove the transmission coolant lines.
   
5. Step 5 Disconnect the radiator supports. 1986 through 1992 models will have two upper retaining screws for 3.0 liter and SHO engines. 3.8 liter engines will have two driver's side hex nuts and two passenger side screws. All other models have either the upper screws or the combination of right hand hex nuts and left hand screws.
   
6. Step 6 Tilt the radiator backwards toward the engine and lift it out. Fit the new radiator into the support and replace the support screws and nuts. Reattach the hoses and wires in reverse order.
   
7. Step 7 Flush the new radiator with either water or a commercial flush treatment. Connect your battery terminals and replace the coolant and let the engine idle for 5 to 10 minutes with the heater on and the radiator cap removed. Top off the coolant as necessary.
   

the valve is on the back side of the driver or passenger radiator side tanks (engine side) crawl under the car to see it or open it.