How much is coolant now a days? Apparently, you're supposed to change it out every so often since older coolant starts to become acidic, and starts to eat away at your radiator, engine, water pump, etc. If you stick you stick a voltmeter lead in the coolant, and the other touching ground, it'll give you a small voltage. I forget how much was "acceptable" but it should be very close to zero.
Either way here's some specs:
4.6L 19.0 L (20.1 quarts)
4.6L — with aux. rear heat 21.0 L (22.2 quarts)
5.4L 21.0 L (22.2 quarts)
5.4L — with aux. rear heat 23.0 L (24.3 quarts)
For the 5.4 3V
Base radiator without aux. rear heat 18.4 L (19.4 quarts)
Base radiator with aux. rear heat 19.6 L (20.7 quarts)
Heavy duty trailer tow radiator without aux. rear heat 18.6 L (19.7 quarts)
Heavy duty trailer tow radiator with aux. rear heat 19.8 L (20.9 quarts)
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You can drain the radiator yourself. On the bottom, there is a draincock that you open. Granted, doing it this way one lets you get out a little less than 80% of the total coolant (per the service manual).
Here's how to fill the coolant back up (per the service manual):
1. Fill the radiator through the degas bottle until the coolant level is between the "COOLANT FILL LEVEL" marks.
2. On the electronic manual temperature control (EMTC), move the temperature blend selector to the full WARM position. On the electronic automatic temperature control (EATC), set the temperature to 32°C (90°F).
3. Run the engine at idle until it reaches normal operating temperature.
4. Add the correct coolant mixture to the degas bottle until the coolant level is at the upper "COOLANT FILL LEVEL" mark.
5. Turn the engine off and allow it to cool.
6. Repeat Steps 1 through 5 until the degas bottle level is correct, with the engine cool.
7.
CAUTION: If the air discharge remains cool and the engine coolant temperature gauge does not move, the engine coolant level is low in the engine and must be filled. Stop the engine, allow it to cool and fill the cooling system.
Select the maximum heater temperature and blower motor speed settings. Position the control to discharge air at the A/C vents.
8. Start the engine and allow it to idle until it reaches normal operating temperature. While the engine is idling, feel for hot air from the A/C vents.
Hot air should discharge from the A/C vents. The engine coolant temperature gauge should maintain a stabilized reading in the middle of the NORMAL range and the upper radiator hose should feel hot to the touch.
9. Shut the engine off and allow it to cool.
10. Check the engine coolant level in the degas bottle and fill it as necessary.
11. Repeat Steps 7 through 10 as necessary.
12. Check the cooling system for leaks.
13. Install the pressure relief cap to the degas bottle.