When you should change the oil in your car


August 13, 2017 by quirkyuncle@gmail.com

Comparison of 7500 mile vs 15,000 mile oil change intervals

The oil change interval that your car maker recommends might not be the best for long-term engine health.

I was appalled to see the difference in oil condition between my two cars when changing the oil yesterday. Both cars are at just over 100,000 miles and both have used only synthetic oil.

  • The following two images of inside the engine, taken through the oil filler opening, are with synthetic oil being changed after 7500 miles.

    7500 mile example 1
    7500 mile example 2

  • 15K mile example 1
    15K mile example 2

I’ve been changing oil in the first car every 7500 miles since I bought it some 70,000 miles ago. The second car just came off of its free oil changes every 15,000 miles factory oil change interval – I could not change the oil myself at 7500 miles or the dealer would refuse to change it again at 15,000 miles because sensors inside the engine read the oil condition as okay. How rude!

Aside from the dirty look of the 15,000-mile-old oil, the most disturbing part was how the dirty oil felt and behaved. The 7500-mile-old oil still felt like oil: smooth and slippery. The 15,000-mile-old oil felt sticky, more like grease. It stuck to everything and was difficult to wipe my tools clean. In the photos, this explains why you see so much more oil on the internal engine components of the second car images – the oil was stuck there!

So, what’s the deal?

The intervals between oil changes have steadily risen since I started working on cars a number of years ago. Advances in chemistry and technology have certainly contributed toward reducing the requirements for routine engine maintenance – it’s a good thing. However, in the current environment of free oil changes for 100,000 miles, car makers have found an easy way to save money by reducing the number of oil changes that they need to perform for customers.

If you lease a car plan to trade your purchased car in every few years, it doesn’t matter much. If you’re like me, buying used cars and keeping them for a long time, it is very important that you do whatever basic maintenance you can to keep your vehicles in tip-top condition. Oil changes are one of the most important things you can do to keep your engine healthy.

The recommended interval

Many car makers specify an oil change interval of around 15,000 miles for synthetic oil and 7500 miles for conventional dino oil. While it is true that the oil is still lubricating at this point, it has become hideously dirty and, as discussed above, seems more like grease.

A reasonable oil change interval that many car enthusiasts recommend is 7500 miles for synthetic oil and 3000 miles for conventional oil. I’ve followed this pattern for many years with good results. It would be my personal recommendation.

Adaptive oil change intervals

It seems like a really cool idea that your car can tell you when the oil is at a condition where it needs to be changed, based on some sort of internal sensor analysis. Being a person who likes to protect the planet and save money, it seemed the best of both worlds… until now.

The car with the 15,000 mile oil change interval, shown above, does include a sensor system that adjusts the oil change interval around a 15,000 mile baseline. This adaptive system indicated that the oil in the car still had about 750 miles of useful life left in it.

I beg to differ.

Hope springs eternal!

If you are totally depressed that you have been waiting too long to change your oil, it’s okay. If you start changing the oil at earlier intervals now, much of the gunk should get cleaned away over time. I’ll post new photos here of the improving condition of the engine formally known as having a 15,000 mile oil change interval after each upcoming oil change.

Related postings:

Oil is the life-blood of your engine. Keep it clean and healthy!

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