Castrol Oil

[Hib Halverson]

There are several very good engine oils that do not meet 4718M.

There are also some really s***y oils that don't meet 4718M.

Keep in mind that 5W30 oil, which the vast majority of GM engines made since the late 70s call for, is suggested mainly because GM uses it in the engines it uses for EPA emissions and fuel economy certifications.

Just because the Owner's book calls for it doesn't mean it's the best choice. In fact, there are cases where the Owner's Manual simply says 5W30, but the Service Manual may list 10W30 as an alternative.

My personal rule is that 10W30 is a better choice in all cases except cars operated regularly in very cold weather (such as winters in Alaska, the UP of MI, Minnesota or northeastern Maine) and is a much better choice in cars operated in warm areas such as Southern California, Arizona, Florida, Texas and other places it gets really hot in the summer and stays temperate in the winter.

As I spend most of my time in California and the "desert" southwest, I've never used a 5W30 oil of any brand. I always use 10W30.

 

[Curious George]

Most people are using "synthetic" oil and they do not even realize it. What I mean by this statement is that oil that is "hydroisomerized" can be classified as as "synthetic" in the USA only.

Most "regular" oil falls into the Group ll category, which is more than likely hydroisomerized. A "solvent" refined oil still has an inferior molecular structure compared to hydroisomerized oil. This is why you can go longer between oil changes nowadays than in the recent past. Better additive packages too have helped wring out some extra mileage from Group ll oils. If a Group ll oil is refined slightly more, you now have a Group lll oil.

Then there are "true" synthetics (Group lV and V), which are also very good oils. In my opinion, both synthetics have good properties for engine use. Some better than others.

CG