5w20 syns all the same but have specs changed?

[JCM35]

my 2005 focus 2.3 has almost always had syn in it. It seems that when the cold months set in i have a harmonic reasonance coming from my engine at med to high revs. Car has 73 grand on it and it seems it happens after the oil has a few grand on it. My current fill of synpower 5w20 has 3 g on it. I figure that all syns in the 5w20 are equal and couldn't tell the difference in UOA'a but is it time for a step up in weight or has the 5w20 spec changed since i really paid attention to oil in 2006. Have used synpower and platinum both 5w20 for the last 4 years. Would syntec 5w20 being thicker help? Wasn't a new spec for all oil beginning in 2009?

 

[Bryanccfshr]

I would not think harmonics is oil related. My first look would be at the belt tensioner(s) Alternators and other rotating equipment. AN AC clutch could cause this too.

 

[dnewton3]

Agreed. It's likely a developing mechanical issue; not lube related.

 

[JCM35]

Probably right. it has done this in the winter the last 3 or so years. warmer weather nothing. Thanks for the replies.

 

[mechtech2]

Any rubber is stiffer in winter. Motor mounts will transmit vibration more in winter. If you have an harmonic damper on the crank, it will act differently in cold weather.
You exhaust gas is being cooled along the pipe's length much faster, and results in denser gas in the pipe, which affects running and possibly 'feel'.
But mostly: engine , trans, and exhaust mounts are the key factors.