Friday Rant: How Long Can you Go Without Changing Your Oil?

Spend Matters welcomes a Friday Rant from our resident "car guy" (and lead analyst) Thomas Kase.

As so many other things exclusively "known to the State of California," they now want you to stop thinking about this and instead let an online calculator decide oil change intervals for you. Reference this story for more detail. It is a well-intended article, and as usual, "well-intended" and "California" go so well together. 🙂

It is true that 3,000 miles between changes is actually too frequent for many cars. But it all depends on what kind of car you have, your driving pattern, the filters and oil you use, the local climate, even the regional air quality where you drive.

Short driving cycles -- below 20 minutes -- are the most destructive since they don't allow the oil to be fully heated and boil off water and other byproducts like acids that accelerate additive breakdown. So, if all you do is hop in the car for short 10-15 minute runs to the store, probably wise to stick to the 3,000 mile interval.

Even if you don't drive your car at all, time still works against you (remember that the big oil molecules don't break down -- this is why oil can and should be recycled 00 but the additives do). Additives are what help protect the engine during startup, and startups in turn is what causes as much as 90% of engine wear! Additives die from oxygen and acid exposure over time more than anything else, which is why you should change the oil every six months even if you only drive a few thousand miles per year. Drivers that let their engines run longer than 20 min each trip can sometimes extend oil change intervals to 12 months and go beyond 10,000, even as much as 15,000 miles -- these drivers would be in the sweet spot for the current California awareness campaign.

In fact, to some degree oil even goes bad sitting in unopened jugs on the shelf (albeit slowly) ExxonMobil recommends a five year maximum shelf-life for engine oils, including Mobil 1, their high-end product. More engine wear is actually caused by corrosion than by actual mechanical wear, especially in critical areas such as cylinder walls, piston rings, and cam shafts. Especially so in countries with fuels higher in sulfur (relative to the EU region, permissible sulfur levels have been higher in the US for a long time) albeit nowhere near the levels permitted in countries like Mexico and India. In fact, California's current low-sulfur content standards still permit 20ppm by weight whereas EU regs permit only half that or 10ppm by weight. India, on the other hand, permits as much as 150ppm. Sulfur can be removed as part of the refining process through catalysts -- at a price of course.

About additives, the amounts of many proven additives such as ZDDP (ZincDialkylDithioPhosphates) have been reduced over recent years as a result of the EPA's drive to increase catalytic converter longevity. Unfortunately, the zinc and phosphate additives help the engines last longer without turning into oil smokers by both increasing lubricity, prevent corrosion and reduce oil oxidation. Well-intended activities biting Californians in the rear again... That said, used oil analysis done at "Bob is the oil guy" a popular source of information regarding automotive lubricants have done research that claims that the majority of cars and light-duty trucks on the road today do well without these additives. However, for those of us with older vehicles -- and I have a few from the '60s and '70s -- there are excellent dinosaur-based oils such as Brad Penn, Redline and others that still have all the ZDDP and twice the caffeine! There are also ZDDP additives sold by the bottle for those of us who don't have to worry about catalytic converter life. Recent research points to titanium-based additives as a replacement – this metal plays nicer with the catalytic converters. Most SN/GF5 rated oils are formulated with new, proprietary, compounds that replace the missing ZDDP and phosphorous compounds. For all those with older cars however, the right additives are especially important -- and California is known for its many well-preserved vintage cars. Let's keep them running on good oil.

Changing oil is cheaper than paying for engine repairs, and "better safe than sorry" is my personal maxim. One of my vehicles technically only requires a change once per 12,000 miles but with a complex four-cam engine and other complexities, I prefer to change twice as frequently, or once every six months.

The website reference at the top of this article suggests using another site to see what the factory recommendations are for your vehicle -- but it only goes back to model year 2000 and even for the years covered, not all brands are listed (Land Rover is an obvious omission).

The article suggests that oil consumption can be reduced through inflating tires -- an interesting suggestion -- the liberal panacea to all automotive ailments! Another suggestion is to avoid idling, which I also wonder if it is such a great suggestion. Sure, it cuts fuel consumption, but increases the number of engine starts. It will be interesting to see how cars with the much-touted auto-start feature will last compared with the same car with traditional operation.

Another funny line from the article: "the 3,000-mile oil change -- made sense years ago, when we had cast-iron block engines with cast-iron pistons. That would have been nearly 100 years ago. I think the Ford Model T which came out in 1908 must have been one of the last to use cast iron pistons. Personally, as a bit of an auto nut and having worked in the automotive industry, I have never even seen pictures of any cast-iron pistons -- aluminum alloys are what has been used in pistons since at least the 1920s. While picking nits, few of us drive "power trains" cars have a powertrain... 🙂

Back to oil changes, the truth is not as easy as recommending any specific mileage . But in the interest of prudent financial asset management, all of us should assess the factors that impact the longevity of our vehicles -- a healthy car is going to last longer, have lower operating costs, and a higher resale value.

For those managing and setting policy for corporate fleets, I am sure this an even more important area to manage total cost – at Spend Matters we would be most interested in hearing from those with access to real world fleet data over time and their experience regarding oil changes. Granted, fleet use typically means daily operations so the detrimental effects of prolonged storage or only short trips probably don't apply. Anecdotally I have been told that a major delivery fleet operator changes the oil in their large trucks every 40,000 miles based on used oil analysis using conventional oils – but this decision is based on careful research and a consistent usage pattern, which doesn't look like the way I use my car.

For all readers (and especially fellow amateur tribologists) I recommend Bob Is The Oil Guy for further research.

- Thomas Kase

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