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.

1 Answer 1


Once your system expels as much fluid as it can via the pump there is still an additional amount of fluid that is left in the block and other areas that the pump can't push out because there isn't enough fluid and pump is just attempting to push air through the system.

Some engines have block drain plugs. You would need to remove those, allow to drain and reinstall them....but your vehicle apparently doesn't have one.


As @rpmerf indicated, you can get a specific gravity test tool at the auto parts store, it's called a hyrdrometer. Hydrometers only work for Ethylene Glycol based coolant.

Propylene Glycol can't be read by a hydrometer, up to 70% concentration specific gravity increases, above 70% SG decreases.

  • 1
    Yes. That's where the extra coolant is at is in the block. Unless you get the block drained, you'll have leftover there. Jan 4, 2016 at 20:55
  • Thanks very much for the answer. I'm a software developer not a mechanic so I wasn't sure I was explaining it properly. Great info. This helps to clear up my confusion about the relatively small amount of fluid it took. It may also be a cause for concern since it was previously filled with water, which will in turn dilute my 50/50 antifreeze.
    – raddevus
    Jan 4, 2016 at 21:28
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    There is a test tool for coolant concentration.
    – rpmerf
    Jan 4, 2016 at 21:33
  • 1
    I edited the answer with additional information. YW. Hope this helps you out. Jan 4, 2016 at 21:37

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