Oil Change Intervals

Time to talk about extended oil change intervals, or OCIs. If you're running a full synthetic oil, and not extending your OCIs, you are pretty much pouring money down the drain. Synthetics are great for a lot of reasons, a big one is their resistance to wear. 

The key to extended OCIs is UOA (Used Oil Analysis). These are tests that can be done on oil samples to tell you everything you need to know about it. Included in UOAs are measurements of many things, including metals, dirt, fuel water, etc. Some metal in your oil is good. ZINC for example is a common additive to prevent wear and reduce rust. Some metals, however, like aluminum indicate wear of engine parts, and could point you to some internal damage. Iron content is the only component that accurately shows the oil's wear life, the rest are all relative. 

In addition to telling you if you have excess wear, or fuel or coolant cross contamination in your oil, UOA allow you to check oil viscosity

 and TBN (Total Base Number). These two factors allow you to judge how much life is left in your oil, assuming you dont have too much metal or dirt floating around; if that's the case, its time to look at your filter.

Viscosity is key because oil that is too thin will vacate areas where metal parts come together. This "squishing" of the oil is called shearing. This is important and I will touch on that later. Assuming your UOA says viscosity is within range, you are good in that department.

The other life meter is the TBN. Most people agree that a TBN of <1 means it's run its course and it's time for an oil change. For example, Amsoil Premium Diesel Motor Oil 5w-15 has a TBN of 10.4 off the shelf.

The graph to the right shows test results done over 400 operating hours in a fleet, using various oils. The top chart illustrate Amsoil's ability to maintain TBN levels greater than many competitors. Valvoline Premium Blue Extreme also does very well in this test, while the other three decrease at an accelerated rate.

The bottom graph shows the resistance to shearing by maintaining viscosity. Amsoil again proves to be the top dog in this test. Shell Rotella T6 also did well in this test, however eventually well to SAE 30 standards. Valvoline Blue, our previous runner up, didn't fare so well in this test.

If you are interested in having your oil tested, please let me know. I can sell you some oil test kits. It is very easy; just drain some oil into the provided bottle, and mail it off; both prepaid and non-prepaid postage test kits are available. The results will be back soon!