John,

I'm not so sure on the tolerance thing you mention, since Ford approves the use of 5W20 in engines dating back to 91 or 92. IIRC, the 91 or 92 5.0L V8 is on the list of approved applications for the 5W20 oil.

I suspect that oil is simply an attempt to get better fuel economy.

I am seriously considering 5W40 from Mobil 1 Delvac (typically used in truck, but does carry an SJ rating meaning it is API certified for Spark ignition (S=Spark such as gasoline and C=compression ignition.)

See the Delvac 1 info here: http://www.mobil.com/mobil_lubes/onhighway/products_services/delvac1/specs_content.html

I do have some Shell Rotella T 5W40 synthetic, I plan to use in the Buick this winter. I picked up two gallons of this synthetic for about $12.18/gallon at the local Wal*Mart.

The Rotella T, like the Delvac1 is a 5W40 synthetic, and meets the latest API gasoline engine standard, SL.

http://www.rotella.com/rotella_t_synthetic.html

But I'd have a hard time with 5W50 or the 20W50 stuff in most Contour applications.

TB

Tony Boner
Personal: 98cdw27@charter.net Work: tony.boner@sun.com
Saving the computer world from WinBloze as Unix/Solaris/Java Guru http://www.sun.com
1998 Contour SVT Pre-E1 618/6535 Born On Date: 4/30/1997
Now with Aussie Bar induced mild oversteer.