I run synthetic 5w20 in my NA 1998 V70 with no problem. I do change it every 3K and the engine has 125k on it now.
The 2002 Volvo S60 has 20 valves.
The 2006 Volvo S60 has 20 valves.
The 2007 Volvo XC70 has 20 valves.
The 2004 Volvo XC70 has 20 valves.
The 2010 Volvo C70 has 20 valves.
The 2014 Volvo S60 has 20 valves.
The 2003 Volvo XC90 has 20 valves.
The 2004 Volvo XC90 has 20 valves.
The 2003 Volvo XC70 has 20 valves.
The 2009 Volvo C30 has 20 valves.
The 2004 Volvo C70 has 20 valves.
The 2004 Volvo S80 has 20 valves.