Don't Change Your Oil Every 3000 Miles

The original 1957 Chevrolet Owner's manual claimed that you should change your oil every 2000 miles. It also mentions that you should repack your wheel bearings every 10,000 miles. That was 54 years ago.

Today, there is no mention that one should repack their wheel bearings. In fact, I can't recall seeing that as a maintenance procedure in my driving life time. We sure have come a long way. So, why do we need to change the oil in our cars every 3000 miles? Surely engine oil has come a long way since the late 1950s and early 1960s, right? Well, yes, oil has come a LONG way since those days. Today's engine oil is so good that they have had to change oil ratings.

In the old days SAE 30 or SAE 40 was the oil you put in your engine. The "30" and "40" was a grade or weight of the viscosity of the oil. The viscosity determined how well it actually lubricated. The lower the number the "thinner' the oil was. The thicker the oil was, the better it lubricated. Thus an SAE40 was a better lubrication than an SAE 30.

It isn't all about the viscosity. Engine oil that did not move easily at standing temperature and could not lubricate the engine very quickly. So, most of the engine wear came at start up where the engine oil was cold and not yet flowing through the system. So there needed to be a balance between high viscosity for lubrication and low viscosity so the oil would flow quickly when it was cold. To reduce wear at start up, you needed a thinner oil. To reduce wear during normal operation, you needed a thicker oil.

Enter "multi-grade " oil. No longer is engine oil generally marked with SAE40, it is usually marked "10W-40." This is a "multi-grade" oil that has the characteristics of having the lower viscosity when it is cold and the higher viscosity when it is warm. Today you can even get 5W-50 (with 5W-60 on the way) oil which is very thin when it is cold and doesn't get much thinner when it is hot. That should reduce the over-all wear on the engine significantly.

Don't forget oil filters! Yes, oil filter technology has not lagged either. High efficiency oil filters remove more debris than ever before while also allowing for better flow through the filter improving fuel efficiency.

After decades of automotive development, are we to believe that oil life is still only 3000 miles? Well, evidently we are supposed too. I usually try to avoid conspiracy theories, but it does make one ask questions. If the 3,000 rule of thumb were to change to 6,000, an entire industry could lose 50% of its revenue over night.

Well, there have been studies that have been published, some cost money from the SAE and some are hard to find. One study performed by the state of California is available on line at: http://www.calrecycle.ca.gov/UsedOil/OilChange

So, there you have it, 3,000 miles? Don't be sheep. 5,000 is OK. 6,000 is OK. If you do mainly highway driving, a synthetic oil may get you 25,000 miles. You'll save some money, save some natural resources, and you won't be a sheep.