Prestone has two flushes. I can't recall their names . The milder one is safe to use. The more powerful one may not be as it is an acid. I used it once long ago to try to clean out some white crystaline deposits from the tubes in my radiator. I don't know if these deposits were inside the engine as well. As I recall, the flush did remove quite a bit of the deposits. However, that was an all-iron Americam V-8. I'd be a little cautious about using this flush on the Volvo engine because of the aluminum head. What I'd be most concerned about is messing up the headgasket seal between the aluminum head and the iron block.

This would be a good question to pose to the entire Brickboard. There is probably more expertise than mine on this subject. You could also do a search on this site using "radiator flush".

Why do you feel the engine needs to be flushed? Is it overheating?