SWUtah, I don't know the real reason, but you might be onto something with "marketing hype to drive down the perceived cost to maintain the vehicle".
I have an old friend but we don't talk much these days, he's an automotive engineer, used to race TRD#1 in SCCA. He was my source for the more complicated aspects of automotive design and theory. Back in my day of really wrenching on cars, because you had to, OCI was 3 months or 3k miles. I'm just not comfortable going more than 5k even with synthetic, and here's why. Engine oil, unlike let's say the transmission, gets exposed to and mixed with all the combustion byproducts. Over time this degrades the oils ability to protect the internal moving parts, and with conventional oil sludge forms. As my old high school auto shop teacher said, when you mix (synthetic) oil, gas, water, etc. you get oil, gas, water, etc. but not sludge. That may be overly simplistic, but there is a kernel of truth in that old man's wisdom.
Regarding viscosity, Toyota, in my 2009 recommends 0W-20 or 5W-20, they further state 0W-20 when it's cold to help with cold starting. But if one uses synthetic I would argue that you can stay with the 5W-20 in cold weather as synthetic oils flow better in cold conditions compared to conventional oils. This holds true in manual transmissions, transfer cases, and differentials, anyone switch to synthetic in a tranny or transfer case and feel immediately how easy it'll shift? I may try bjowett's idea of 5W-30 during the summer in mine as I have the cold engine knock under load (not happy at all about that).
For further argument, the engineer buddy used to say when an engine is fully broken in, you could just change the filter at every other OCI due to the lack of particulate in the engine.
I have an old friend but we don't talk much these days, he's an automotive engineer, used to race TRD#1 in SCCA. He was my source for the more complicated aspects of automotive design and theory. Back in my day of really wrenching on cars, because you had to, OCI was 3 months or 3k miles. I'm just not comfortable going more than 5k even with synthetic, and here's why. Engine oil, unlike let's say the transmission, gets exposed to and mixed with all the combustion byproducts. Over time this degrades the oils ability to protect the internal moving parts, and with conventional oil sludge forms. As my old high school auto shop teacher said, when you mix (synthetic) oil, gas, water, etc. you get oil, gas, water, etc. but not sludge. That may be overly simplistic, but there is a kernel of truth in that old man's wisdom.
Regarding viscosity, Toyota, in my 2009 recommends 0W-20 or 5W-20, they further state 0W-20 when it's cold to help with cold starting. But if one uses synthetic I would argue that you can stay with the 5W-20 in cold weather as synthetic oils flow better in cold conditions compared to conventional oils. This holds true in manual transmissions, transfer cases, and differentials, anyone switch to synthetic in a tranny or transfer case and feel immediately how easy it'll shift? I may try bjowett's idea of 5W-30 during the summer in mine as I have the cold engine knock under load (not happy at all about that).
For further argument, the engineer buddy used to say when an engine is fully broken in, you could just change the filter at every other OCI due to the lack of particulate in the engine.
