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Synthetic vs Conventional Motor Oil and Change Interval

Perhaps it’s time to re-evaluate both the motor oil used in your vehicle and how often you replace it. The old rule of thumb was that motor oil should be changed out roughly every 3000 miles or every three months, depending on whichever came first. Additionally, it was generally advised to purchase conventional motor oil for standard, daily driving use and only pay the premium for synthetic oils if driving under harsh conditions. While the argument between synthetic and conventional oils has raged for decades, the change interval has happily gone about uncontested.

Lately, even generally conservative mechanics are starting to recommend increasing those intervals upwards of 5000 miles even on conventional oils. Various manufacturers such as Ford, GM, Volkswagen and BMW have published motor oil change intervals from 7500 miles through 15,000 miles when using synthetics. So what’s changed? Aside from the engineering improvements and high tolerance manufacturing within the engines themselves, the technologies behind fuel reformulation (for lubricants and cleaning agents) along with motor oil technology have continued to improve as well. While conventional oils are better than they were when the guidelines were developed, synthetics beat conventional oil in virtually every category of performance. With the general dangers of engine sludge largely in the past, perhaps its time to re-evaluate both oil change intervals and adaptation of synthetic motor oil in your own vehicle.

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4 Votes  - +
Synthetics by ldsudduth

I’ve used synthetics in my car for at least 5 years (Click and Clack show some years back recommended it)—and most especially when the vehicle reaches around 80K miles or so. 5K on the oil changes (again, Click and Clack from 5-6 years back) seems to be about right; as I drive mostly highway. Run a good oil additive and you should be fine every 50K or so and you should be fine.

3 Votes  - +
I Opted For Synthetic by VnutZ

I finally switched to synthetics in my Jeep after 15,000~ish miles when I decided to start doing my own maintenance. The savings I made on not paying for labor made it easy to justify the expense of synthetic (about an extra $3 per quart). I tried Royal Purple 5W-30 (for the winter season) but then switched to Mobil 1 10W-30. I can’t say that I’ve seen any improvements to fuel efficiency, but there haven’t been any declines either.

There were many studies that led me to make the change, although one stands out in memory involving either a Formula-1 or Indy car. IIRC, after every race, the engines are taken apart to study them for performance and weakness. One of the most commonly noted weaknesses were that the cylinder walls were usually scored by the pistons. After a team switched to synthetic, they noticed that for several races, the engine cylinders were perfectly smooth, unscored and "like new". Basically, any scores in the cylinder have the potential of allowing explosive energy to get past the piston/cylinder seal – robbing you of power and damaging the engine. This is one of synthetics arguments towards prolonging engine life – the fact that various impurities, etc. aren’t present to cause such harm.

Anyway, my oil change intervals are between 6000 and 8000 miles now. I was always a 3000 mile changer on conventional oil. 33,000 miles later and no problems (my engine is working a little extra to turn big 35" off-road tires, too). It’s actually cheaper, too, to pay a little extra per unit but buy half as much oil in the aggregate.

3 Votes  - +
The car knows... by johnny_boy

A friend bought a new BMW and asked about when the oil should be changed. He was told that there was no recommended time or mileage, but that instead the car would let him know when it was time. Sure enough, at about 12000 miles, the "Change Oil" indicator lit up. His guess was that there’s some turbidity or acidity sensor keeping watch on the oil. A nice touch, that, although I bet the oil companies prefer the 3000 mile recommendation!

Because I also usually do my own maintenance, at least in the warmer 3 seasons, I usually still shoot for the 3000-mile mark, knowing that by the time I manage to get to it, the mileage will actually be around 5000 miles.
Years ago when I actually adhered to the 3000 mile oil change I had a tenant who would take the used oil from me and pour it into his really crappy car which burned about a quart per trip. It worked out great because I didn’t have to worry about disposing of the used oil.

One old wives tale I remember hearing around the garage was the statement "You can’t mix synthetic oil with regular oil." Apparently this is not true as some companies sell a mixture of the two motor oil types as one of their products.

I switched to synthetic oil during the early 90s. I hate changing oil and being able to go twice as long was the appeal to me. I was raised to change oil at every 2,000 miles by my dad. Arguments over overkill went on and on. The secondary motivation was that I wanted to get away from reliance on oil. Synthetic seemed like a good solution at the time.

One observation of mine is that older cars that don’t run well after switching to synthretic, start running better. One car used less oil after a switch. I think that the differences start showing up once the odometer starts turning over. My 93 van turned over for the second time last summer. Performance and mileage hasn’t degraded as one would expect. The engine hasn’t been overhauled either. I still don’t use much oil and I believe my long term use of synthetic is the reason behind this.

I just check the oil regularly and change it as needed. If the oil is dirty, I change it. Sometimes it happens at 7,500 miles and other times it occurs at 15,000 miles. I follow my car’s cues.

I’ve wondered since the gulf war, is what if all Americans were to switch to either synthetic or ssynthetic blends. How much less oil would be be used each year? What impact would that make on our economy and consumption of oil? Would be nice if synthetic furnace oil were to be in existance.

0 Votes  - +
Once per year by Occams

I change the oil and the two oil filters on my turbo diesel Land Rover Discovery once per year. This vehicle is used mostly for towing my (2 ton) boat, long distances, and usually does not do more than 3000 miles per year. I use relatively cheap Shell oil recommended for diesel engines. Five years now and no problems on a car with a bad reputation for engine problems.

I just don’t believe that oil goes bad after three months on an engine doing low miles.

0 Votes  - +
i think by diegomarad

id go with synthethic

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