If you're at all handy, then a radiator drain, flush, and re-fill is very
straightforward.
The advantages: Don't have to wait on a shop; you know exactly what was done;
you can put in the coolant you think is best; you save money; you'll probably be
more careful; you're calling the shots.
Disadvantages: Your hands get dirty. You have to locate someone that will take
the old coolant (not a big deal; state laws tend to be supportive). You have to
be careful not to leave puddles of coolant (it will kill dogs and cats).
My 1991 Civic's owner's manual has instructions for this. Maybe yours does, too.
I would definitely not do this without the manufacturer's instructions.
I think the most common hang-up comes at the step for taking off the engine
block drain bolt. A lot of people here, including myself, skip it, because the
engine block drain bolt is very tight, it's hard to get to, and the bolt head
isn't optimal. (I did get if off once, however. So it's worth a try.) I just
drain as much as possible through the radiator drain plug orifice, instead, then
fill, idle the car, drain, and refill repeatedly until the drainage runs clear.
I calculate how much water remains in the engine block after the last flush and
then add undiluted coolant to achieve the right ratio of undiluted coolant to
water.
I think the consensus here is to use Honda's own OEM coolant. It costs more but
its guaranteed (by folks here, and there's a lot of experience on this) to
maximize the life of your Civic's water pump. The water pump is persnickety when
it comes to coolants.
I myself am experimenting with the Orange Dex stuff, allegedly designed for
aluminum engines and imports like Honda, as well as long-life. Thirteen months
and all's well. But I have the time, money, and inclination to experiment a
little.
I am thinking of replacing the radiator coolant more often than recommended,
like 1.5 years or 20,000 miles, whichever comes first, instead of 2 years or
every 30,000 miles.
