<VV> LM Correct Oil Viscosity

[Dale Dewald]

At 22:17 4/15/2011 -0400, Bob Hall wrote:

>With all the discussion about engine oil I went back to my owner's manuals
>for '66 and '68 and the service manuals for the same years.  In 1965 the
>single weight oil recommended for operation above 32 degrees F was 30.  In
>1968 the single weight oil recommended for operation above 32 degrees F was
>20.  30 weight oil was only recommended for operation at temperatures 90
>degrees F and above in 1968. I have never used 20 weight oil in any of  my
>Corvairs.  I have used 30 weight oil almost exclusively except in  winter 
>when
>I used a good quality 10W-30.  In high summer I have also  usually used a
>single 40 weight oil.  I also changed the oil every 2,000 to  3,000 miles
>regardless of time.
>
>And this was not synthetic oil of course.  The single 20 weight oil  was
>being recommended for A.I.R. smog engines that could and often did  run 
>hotter
>than the earlier engines.  Was GM trying to get us into  Vegas early?

No, I don't think so.  I would not be surprised if GM discovered the same 
effect others on this list have discovered; thinner oil runs cooler.  The 
bearing loads and clearances on the Corvair engine are not so high or large 
that a heavy oil is needed for lubrication.  A thinner oil flows easier 
(less pumping friction, better splash lubrication) and does not form as 
thick of (insulating) boundary layer against the rocker covers and oil pan, 
making these surfaces more effective for cooling.

I have always used 10W-30 oil in our Corvairs, and either 5W-30 or 5W-20 
for winter back when we drove them year round.  Currently, our Corvairs are 
only driven when there is no salt on the roads and get a yearly change of 
Amsoil type ACD 10W-30/SAE30.

Dale Dewald
Hancock, MI (8" fresh snow this weekend)