Unless your engine is always on the ragged edge of overheating, I'd just
change the coolant every year or two. You don't say what kind or model
car it is but in my experience a surprising amount of overheating (and poor
performance also) is caused by insufficiently advanced ignition, especially
if it was tuned by someone not too familiar with Volvos. They like a lot
of ignition advance.
--
George Downs Bartlesville, Heart of the USA!