There may be good reason to deviate from the grade specified by the manufacturer, since a single grade for all purposes recommendation is obviously a compromise.
There was a time when every OM contained a temp/visc chart to guide in the selection of appropriate oil grade.
Cars as late as our '09 Forester had such a chart.
The warranty denial issue is nothing more than a straw man.
While the API spec met by an oil might be revealed in a UOA by the ZDDP levels, no UOA can tell you what the original SAE grade of a used oil was when new.
Now, a 20W-50 might be pretty obvious, but a 5w30 versus a 0W-20? Too close to call after any amount of time in service. Oil can and does both thin and thicken in service.
The whole purpose of this site is to exchange ideas and experience about what works and what doesn't work as well.
If you learn nothing else here, you should learn that oil grades thicker than recommended are commonly used with good results as are thinner grades more rarely.
Engines aren't nearly as sensitive to oil grade as some people seem to think.
There was a time when every OM contained a temp/visc chart to guide in the selection of appropriate oil grade.
Cars as late as our '09 Forester had such a chart.
The warranty denial issue is nothing more than a straw man.
While the API spec met by an oil might be revealed in a UOA by the ZDDP levels, no UOA can tell you what the original SAE grade of a used oil was when new.
Now, a 20W-50 might be pretty obvious, but a 5w30 versus a 0W-20? Too close to call after any amount of time in service. Oil can and does both thin and thicken in service.
The whole purpose of this site is to exchange ideas and experience about what works and what doesn't work as well.
If you learn nothing else here, you should learn that oil grades thicker than recommended are commonly used with good results as are thinner grades more rarely.
Engines aren't nearly as sensitive to oil grade as some people seem to think.
