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Should I still get my antifreeze flushed and refilled?

As I wrote in this post:


I partially drained my 2001 Civic’s coolant, at 60k miles. I did not flush it. I got it all out of the main drain plug, under the front center of the car, but I could not get the rest of it out from the “engine block” (I think that’s what it’s called). There’s a bolt next to my air filter–which is really hard to reach, and impossible to turn–which is supposed to contain more coolant, but I couldn’t get it.

I obviously refilled it, so I could use my car.

I’m wondering if I should have a shop re-drain-and-re-fill it for me, or is what I already did good enough?


It is common to not be able to get the block plug loose when draining coolant. Especially if you don’t have a way to lift the car up.

There are two reasons why you replace coolant:

  1. To refresh the corrosion inhibiters in the coolant.
  2. To get the old coolant out before the silicates deposit out too badly, coating the heat transfer surfaces.

The way that most of us deal with the drain plug problem is to drain what we can, refill it with water, start the car and warm it up, drain it again. Perhaps repeat again. At that point, you are about half full of a very dillute mixture of old antifreeze and water. If you know the capacity of your system, you know how much antifreeze you need to add to get a 50/50 mix. If you can get enough water out to make room for that much antifreeze, you can pour in that much pure antifreeze, and top off with water as necessary.

I use distilled water because the water in my neighborhood is VERY hard.

Hardly anyone uses the block drains when doing a coolant exchange. I suspect that they generally don?t even exist. The bolt you wrote of is probably the bleed bolt on top of the thermostat housing. That is to let air out of the highest point of the cooling system after you refill it. You open it a little and let coolant and air bubble out until just coolant is coming out.

Flushing with a garden hose with the rad drain open should suffice. Just be very careful that you don?t introduce ice-cold water to a very hot engine. As Manolito suggested, if your water is hard, a fill, circulate and drain with distilled or deionized water is a good idea. Measure what drains from the radiator and see if that is half the total capacity. Refill with 100% coolant. Removing the lower radiator hose sometimes drains a lot more from the block.

You should be using coolant with no silicates for Honda engines, IIRC. Old fashioned green coolant had a lot of silicates. I don?t think that anyone even makes it any more. Even Zerex green has lower silicates than it used to.