<VV> Oil for your Corvair

[BobHelt at aol.com]

Effective April 2005 the latest SM and GF-4 oil designations were made 
mandatory. SM is the latest API standard, while GF-4 is ILSAC's latest standard. The 
main differences between the two standards is this. 

1) GF-4 has a reduced amount of an anti wear chemical called ZDDP. SM does 
not.

2) GF-4 has a friction reducer added, such as moly, to improve gas mileage.

3) GF-4 is identified by the Starburst on the front of the container. SM oils 
are identified within the donut on the back of the oil container. 

Some people are getting concerned about using GF-4 oil in their Corvairs 
because of the reduced level of ZDDP. But this concern is unfounded. Here's why.

Some multigrades of oil are rated for only SM. These still have the previous 
levels of ZDDP. In addition, oils are still available with the SH, SJ and SL 
ratings, such as SH/SJ/SL. So if you were to use an oil rated as such, you 
would still have an oil with the previous level of ZDDP.

Other multigrades are rated for both SM and GF-4. These do have the reduced 
ZDDP. But (and a big but) the API has introduced a new tough anti wear spec for 
the GF-4 and SM oils that has been approved by GM (even) that compensates for 
the reduced ZDDP level. So this means no more wear using GF-4 (less actually) 
is allowed than for previous oil standards.

Finally, don't get too enamored of high levels of ZDDP. A recent study 
indicated the ZDDP tends to harden (actually a tightening of the molecular bonds) in 
place and cause an abrasion on softer metals like aluminum. Thus the Corvair 
cam bearings could possibly have an accelerated wear from ZDDP.

Regards,
Bob Helt