Yesterday I drained the radiator on a 99 Monte Carlo. Owner's manual states that it should take 11.6 quarts (2.85 gallons).
I removed the petcock, flushed the system by running a hose into the top and running the engine.
I ran the engine and watched the temperature with the hose running non-stop into the radiator and the petcock open and the water running through. Finally, when the engine came up to normal temp I turned on the heater full blast and could feel heat, making sure the thermostat opened up.
After that I shut it all off. Turned off the hose. Left the petcock open and waited another 20 minutes until the radiator was completely drained.
Finally, I went to fill the radiator with premixed 50/50 coolant, but when I did the radiator filled up before even the first gallon was empty. Probably about 3/4 of a gallon.
I capped the radiator up, started it up and checked again later but it seems to still be full.
Can you think of any reasons that might occur?
Is the manual wrong? Does it only take 1 gallon or so?
Do you think there might've still been water in the radiator?
Is it possible there was still water in the engine block or however that works?
Also, I did drain the overflow and there wasn't any in there either. I filled it back to the cold line with antifreeze/coolant.