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I did a coolant flush today on my 07 VW Rabbit. The car is supposed to hold 10 quarts of coolant, however both when flushing with distilled water and especially when adding coolant, the vehicle took way less than expected. With the coolant, it took less than 8 quarts before it was full. I topped it up a couple of times after driving it (side question: is this because air bubbles work themselves back the reservoir as one drives and the coolant circulates?), but we still didn't break 8 quarts.

So obviously I managed not to flush and replace all of the coolant in the vehicle. I looked for diagrams and videos and the only thing I can think of is the overflow reservoir is hidden somewhere and must have the remaining coolant in it. Did I do this wrong?

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My best guess is that you had the heater control on cold so the valve was shut and the heater matrix did not drain.

Anytime a mechanic does this, they put the valve to hot so the heater matrix gets drained and so that when trying to add antifreeze the ratio is correct otherwise one can add the antifreeze for the incorrect amount of coolant.

And it also helps with the bleeding process.

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  • This makes good sense, thank you. With the heater turned up to full, does the car need to be on and/or running, or will the valve open mechanically with the switch? I am very nervous to run the car without coolant in it, so I’m hoping I can just turn the switch to open the valve, flush and renew the coolant and be done.
    – Harv
    Commented Apr 19, 2021 at 1:31
  • Update on this, I flushed again the following day making sure to run the heater while driving, as well as to leave it on hot while flushing. I still didn’t manage get a full 10 quarts out, but I think more came out than the first time.
    – Harv
    Commented Apr 22, 2021 at 4:42
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Not sure if this applies to your VW model. Although when I done a coolant flush on a 2012 VW Polo, which only had the reservoir tank on top and then a drain plug on the bottom (one-way entry system? Not like other cars with also a radiator cap).

In order to get/push all of the coolant out, I had to basically make a seal on the reservoir tank with my mouth (after wiping it down don't want to be indigesting dirt or coolant) and blow into it. This pressured and pushed through a significant amount of coolant out. Your model may have a similar procedure?

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