I just finushed changing the oil in my 350. In the ten minutes it took me, the idle dropped +- 200 RPM. I did change from 30 weight to 40 weight, but is that enough parasitic drag to pull my idle down? what happened? oil pressure is up a little, but not more than 5psi.

 

Yes oil viscosity will definately affect your engine. All that heavier oil takes more power to run the pump and push it through the oil galleys. And you also have that hevier oil flinging around on your cam and crank.

 

Ehh I've run 10w-30 to 20w-50 before and my motor has never lowered in idle. Its not that big of a differance. I'd start to look at some other stuff.

 

I would say it should make enough of a difference also.

noticed the same thing on my mazda

 

well, im having carb tuning and distributor issues, so maybe the extra viscosity is just enough to put me over the edge.

 

strange but my volvo 940 turbo does the same thing come to think of it.

 

I changed from 20W-50 to 10W-30 when the weather started to cool down, and I noticed the idle raised about 100rpm or so, hot or cold.

 

sounds like its a pretty common thing, so i wont worry about it too much.