Just boought a 1999 DeVille. Owners manual recommends 10W30 non-synthetic oil. Says ONLY USE 5W30 if temperatures are below 50 degrees F.
Have a 1999 Corvette. Factory fill is with 5W30 Mobil 1.
Would like to use synthetic oil in the DeVille but wonder if since it has 119K miles on it this might not be a good idea. Don't want to start oil consumption on the 8 year old rings.
Why does Cadillac recommend 10W30 and not 5W30?
Will synthetic oil meeting the Corvette specs hurt or help the seasoned Northstar engine?[sm=bangbang.gif]
BIGHANK

 

Engine should due fine with 5w-30 Mobile 1.Engine holds 7 1/2 qts with filter, dont over fill. 8qts is too much.