Annual coolant changes are unnecessary.  If everyone did this it would
be a huge environmental problem as well.  The problem with coolants is
breakdown of the anti-corrosion additives, which takes about two years
with all conventional coolants and 5 years/50,000 miles with the long
life types, which are all identical and use a completely new anti
corrosion chemistry.

Use 50% distilled water with the coolant if you live in a hard water
area, and yes, there are companies that will test coolant.  An easy test
you can do yourself is to buy some pH test strips from a chemical supply
house.  If they show a shift to acid pH in the coolant change it.

There are also buffers you can add to the system that will neutralize
acids if they are formed.  No Rosion (http://no-rosion.com) is a good
one, and I used it for three years before switching to the long life
stuff (I may use it with the long life anyway!).

After pulling the heads on my worn out (210,000 on the bottom end) 1.9
engine I found there was no pitting on the heads at all after 110,000
miles/eight years.  This period included two years on Autobahn coolant,
three on Autobahn with No Rosion, and three years on the long life.

Anyone need a set of good used 1.9 heads?  $200 + UPS and they are
yours.

Stuart