compnurd said:
if you went from 10w30 to 0w-30 then yeh maybe but not from 5w to 0w
Thought I'd chime in for my first post since I work in the oil industry. First, let's break down a multi-grade oil's classification. The 5w means it meets the cold weather properties of a 5w oil. The 30 means it is an SAE 30 at 100 deg C (close to operating temp). So, the viscosity at operating temperature for 0w30, 5w30 and 10w30 are all the same. The differences come in cold start performance and cold temp pumpability.
As far as synthetics go, the biggest difference between them and petroleum based oil is cold weather performance. Synthetics have much better cold weather performance than their counterparts. However, the additive package (at least in our oil) is exactly the same. So, while the oil itself will stand up better to longer life, the additive package will be used up at the same rate.
I can try and answer any other questions that you guys have.