I'm replacing radiator and a/c condenser on my car. After hitting a deer, they both bent inward and most of the coolant leaked out of the car.

I got both of them off the car and realized I forgot to actually flush the system with distilled water while the old radiator was still on.

I also have the thermostat out so would be a good time to flush; however it would be a pain to connect the old radiator back on with the transmission lines.

Is it necessary? If there's coolant still in the system it isn't much. But I know it's probably not great to try to flush after installing new radiator, so I'm trying to see if there's something I should do now before installing the new radiator and condenser.

I should also add that I did not remove the water pump drain plug, so I don't know if there's more coolant in the system. But since the radiator was empty, as well as the reservoir tank, I can't imagine there's much in the system.

  • What is the year/make/model/engine of the car in question? This is important so I (or someone) can give you proper guidance. If everything you dump in is going to dump right out, just pump water in and let it flow. There's not going to be much coolant left in the system anyway (as far as polluting the environment, etc). The idea of flushing the system is to get all of the old coolant out of it. As long as this is accomplished, you should be in pretty good shape. Dec 4, 2018 at 2:11
  • Yes, sorry I forgot – Chevy Cobalt 2009. Thanks @Pᴀᴜʟsᴛᴇʀ2
    – darnitdiy
    Dec 4, 2018 at 2:17

1 Answer 1


Yes, you can flush the motor with the radiator out. Take a garden hose and put it in the bottom radiator hose or inlet. then tightly squeeze a towel in around the hose. Turn on the hose and wait for the water to run clean out the top hose or outlet.

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