Premature water pump failure. Saw it on my 91 Civic after a
few years of using the Prestone and similar stuff. One
cannot definitely blame the coolant, of course, but other
reports here tend to support the theory. The net may have
more.

I have used the orange Havoline anti-freeze in my Civic
since about 2002, with no problems. The water pump was new
in 2001. Technically, it's due for replacement, but that's
another thread.

Part of the directions for replacing the coolant say to
remove the drain bolt on the engine block. It can be hard to
remove, but you really do want to remove it, since doing so
ensures a good drain and fill. The first time I did this on
my 91 Civic around 1993 it was very difficult to loosen. But
I did not have a deep socket, nor breaker bar yada, and was
not as handy then. Now I find it easy to remove and have
done so with little problems for the last several changes
over some eight years or so.

With the engine block drain bolt removed, you can really
flush the system pretty well, in my estimation, with a
garden hose placed in the radiator mouth, the radiator drain
plug shut, and with the water running out the engine block
drain bolt hole. For the early flushes, catch the coolant
that comes out with the water, since you don't want it
poisoning animals.

A bit of water will remain in the engine block when you are
done. You can do the persnickety calculations to account for
it and compensate with a slightly higher concentration of
anti-freeze, assuming you are using orange Havoline and not
OEM pre-mix. Or you might be fine blowing off the small
amount that stays in the block.

You will want some non-hardening high temperature sealant
for the engine block drain bolt threads. One of the Permatex
sealants says on its packaging it is good for the drain bolt
on the engine block. The sealant is per the maintenance
instructions. You will also need a new gasket for the drain
bolt.

I've been following the thread on Honda brand antifreeze, and I noticed
the comments about Prestone not belonging in a Honda.

I noticed green antifreeze in my 93 civic that I bought from a friend
recently.  What potential hazards am I dealing with?  What's the best
way to get it all out if I'm going to replace it?