We’ve researched this and find that many “experts” disagree on exact numbers. First, check your vehicle owner’s manual. If you don’t have that or need a second opinion, here are some recommendations we’ve come across:
Engine Oil: With a new engine with little or no wear, you may be able to get away with 7,500-mile oil changes, as some vehicle manufacturers say. But recently a fleet owner we know sent full synthetic oil samples from two trucks to the oil manufacturer for testing. The oil had been in his trucks for about 10,000 miles. The oil manufacturer reported that the business owner should be changing the oil in his trucks every 5,000 miles, even with their full synthetic!
Also, as an engine gets older, “blow-by” increases. This is because the rings and valves are not as tight as when new. More unburned fuel gets by into the crankcase, and this dilutes the oil, causing the oil to break down sooner. So if the oil isn’t changed often enough, you can end up with accelerated wear in your engine.
SO… for engines with fewer than 50,000 miles on them we recommend changing the oil every 5,000 miles if you’re using conventional oil, and every 7,500 miles** with full synthetic oil. For older engines, 5,000-mile intervals are still OK, but if you want the engine to last a long time, you can use “High Mileage” oil, which includes additives that help prevent and rid the engine of small leaks, deposits, and sludge. High Mileage oil also usually includes special anti-friction additives which newer engines do not need as much.
**Audi, Jaguar, Mercedes and others have started to use only synthetic oils in their new cars, and they recommend changing the oil every 10,000 to 12,000 miles, depending on the car manufacturer. BMW recommends 15,000 miles, but we have photos of BMW engines that had their oil changed at 15,000-mile intervals, and there is way too much sludge build-up. Toyota is now using and recommending synthetic oil in many of their new vehicles, and they recommend changing the oil every 10,000 miles. Remember, however, that when a major oil manufacturer tested their synthetic it’d been in use for about 10,000 miles, they reported that it should have been changed at 5,000 miles. That may have been because of rougher use, by why take chances?
There are still guys out there who change their oil every 3,000 miles “because that’s what my dad did, and his cars ran forever”. Actually, modern oils are far superior to what Dad used, as are modern oil filters. Also, today’s engines are a result of much better engineering, with tighter clearances between parts, and are made from improved materials (metals and alloys).
In summary, for most vehicles, we recommend changing conventional oil every 5,000 miles and synthetic oil every 7,500 miles at the most. The oil filter should be changed at the same time the oil is changed.
