A good friend of mine about a year ago got a used 700 series Volvo with 120K miles for a very low price. The previous owner installed a rebuild engine 10 years ago after the original engine blew a headgasket and the engine siezed at 50k(his wife was driving the car at the time).

The cars runs beutifull but the only problem is that the cooling system is developing rust deposits and the previous owner recommended my friend to flash the system once per year before winter. The problem with the rust is that the heater core gets plugged with the rust deposits and it doesn't blow any warm air. My friend last time flashed the cooling system/heater core on October 2003 before the winter. Now the car seems to be developing the same problem.

My friend's non-Volvo indy mechanic mentioned that he has seen the same problem with some of the mid nineties Ford Taurus and this problem was due to the manifacturer not treating the engine internally during the manifacturing process. Is it possible that the rebuilt engine manifacturer hasn't treated the engine internally.

Did anyone had any similar problems with their Volvos?
Is there some kind of cooling system additive we can try that might stop the rust? There must be something out there that should neutralize the rust from Forming.

Any ideas?

Thanks

Mike