I just changed the oil in my FJ60 ('85, 160K miles) from it's regular 5W30 to 20W50. Not really for a particular reason, other than that according to the owner's manual 20W50 in the California summer is recommended. Both are conventional oils; the 5W30 always was a "high mileage" oil.
Not expecting any difference, I was surprised that:
1) idle RPM dropped from about 1100 RPM (I have never been able to get it any lower by adjusting the idle speed screw), to about 700 RPM
2) oil pressure is now constant at the second mark, independent from RPM, and even at idle. Before the pressure was a little below the second mark while driving, and quite a bit lower when idling (at 1100 RPM ).
I assume the lower idle and higher pressure at idle are caused by the higher viscosity of the 20W50 oil. Is this a good thing or not? Especially the lower idle, while a nice improvement , makes me think there is now more friction, which may have an effect on mileage (have yet to check this), or wear?
Any thoughts?
Not expecting any difference, I was surprised that:
1) idle RPM dropped from about 1100 RPM (I have never been able to get it any lower by adjusting the idle speed screw), to about 700 RPM
2) oil pressure is now constant at the second mark, independent from RPM, and even at idle. Before the pressure was a little below the second mark while driving, and quite a bit lower when idling (at 1100 RPM ).
I assume the lower idle and higher pressure at idle are caused by the higher viscosity of the 20W50 oil. Is this a good thing or not? Especially the lower idle, while a nice improvement , makes me think there is now more friction, which may have an effect on mileage (have yet to check this), or wear?
Any thoughts?