Hi,

There is no reason to change the oil any more frequently than every
3000 miles just as the manufacturer of every car in the whole world
recomends. The added expense of changing the oil any more frequently
than that could be used to defray the cost of something useful, and oft
neglected. A good tune up will not only extend the life of the car, but
increase performance, and fuel economy. New plugs and wires are a great
idea. A go over of the flame trap(PCV) system is a pretty good idea. A
new air filter is a must if the one included with the car looks worn.
Chemical treatments may not work too well, but an actual pressure
cleaning of the fuel injectors may help. The B series engine equipped
on the 2 series Volvos are basically BOMB PROOF. If a few simple
maintenance procedures are done regularly, you should have 0 problems.
It really is a question of how well, and efficiently you want the car
to run. Then again, when I do buy a used car, I tend to want to change
the oil every 1000 miles for the first 3000 miles or so to clean it out
just in case. Don't skimp on the oil,  But don't go overboard either. A
good quality oil should be good enough, don't go cheap, but there is no
need to put anything special in there either.

I have been driving everywhere in an '86 740 that I absolutely love. It
cost me in fact $500. A couple of oil changes to get the kinks out, and
a good tune up to do all of the preventive maintenance that always
winds up getting done correctively, and voila, I'd drive it anywhere.

Best -O- Luck,
-Z-