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Synthetic oil vs. conventional oil

We have a new car with conventional oil in it. We have 2 older cars, 9 and 10 years, both with about 100,000 miles, still using conventional oil. What are the positives and negatives to changing to synthetic oil at the next oil change for all 3 cars?

The only negative is the cost.

The primary advantage of synthetic is that it may last longer before breaking down and it offers a wider viscosity range for temperature extremes. Personally, I use synthetics in older cars with a 5000 mile oil change interval (I wouldn’t be comfortable beyond 3000 with conventional oil, even thought the manufacture recommended 5000). In my case, the correct viscosity range for synthetic is 5W40, as opposed to 15W40 for conventional. The wider viscosity range provides better lubrication and easier starts in very cold weather. IMO, the cost difference is small enough to justify these advantages.

I use synthetic to increase my oil change interval on my commuting vehicles. For these cars, the interval is 7500 miles. That allows me to time my oil changes so I don’t do one in dead of winter, and allows me to recoup the extra costs of the synthetic. On the “green” side, I am also not using extra oil or extra filters compared to doing 3K or 5K oil changes. For my trucks, I continue with the manufacturer’s recommendation not to exceed 5000 miles, so they get either conventional or a synthetic blend.

Also, I have seen no difference in oil consumption between synthetic vs conventional. I currently have synthetic in my 95 Ford F350, which is the oldest vehicle I have, and it is doing fine.

If you can get the economics to support the change, I would consider synthetic. On the other hand, there are some very good conventional oils and blends that are not very expensive, either. There are rebates available to minimize the cost of the oil also, if you are so inclined. By watching sales and rebates, I have not paid anyone’s list price on oil for over two years.

Synthetic oil has many loyal fans but we have not seen any particular advantage on the bottom line, which is engine longevity. This is true both for new cars as well as well-used cars. You will do just fine sticking with your conventional oil for all your cars.

BTW, 100K miles is not considered particularly high for modern cars. When they reach 200K miles or start burning oil, then you can consider using special high-mileage conventional oil.

First, check the manual of your new car. Chances are good that it specifies synthetic. Many new cars have conditions in their engines that conventional oils will not handle even with more oil changes. It also can invalidate your warranty if you fail to use the specified products.

Synthetic will give you a little better mileage, but you will have to measure carefully to see it as it will not be a big difference. 

I run nothing by synthetic in my newer car as synthetic is specified, the older car may get either.  I guess I am more likely to give it synthetic in the winter due to the temperatures.

The longer interval between changes will probably not offset the additional cost of the synthetic for you. It is most economical for a fleet operator who can reduce staff by extending oil change intervals. You might also run into a filter guarantee that it less than the oil guarantee.

For BMW oil change intervals increased to 15,000 miles due to the use of synthetics. I dont see any advantage in the older engines. Synthetic is expensive (just in case you didnt know)

As stated in may previous posts, Synthetic Oil really shines in EXTREME conditions; extreme heat, cold and under extreme loads, such as towing. Under normal operating conditions, the right weight of normal mineral oil will ensure long life at low cost.

This subject is filled with 20% science and 80% bias.

Synthetic oil is allegedly less prone to heat damage and shearing. However, oil is also contaminated by particulates and diluted by blowby, regardless of whether it’s dino or synthetic. As a matter of fact suspending the particulates is one of the oil’s functions. It’s my belief that oil and filter should be replaced in accordance with the owner’s manual schedule whether you’re using dino or synthetic. The goal is to extend the life of the engine, not to extend the life of the oil.

Also, in 40 years of car ownership I’ve only used dino and have never worn out a single engine ever. Even after 338,000 miles. The 338,000 mile vehicle got totalled at that mileage. It never burned oil. Never wore out. Dino oil changed on schedule still maintains a barrier between the wear surfaces. And no oil will save an engine that’s now well designed or manufactured.

I’ve seen lab tests that demonstrate the superiority of synthetic under extreme conditions, but I’ve yet to see one single study that analytically connects better engine longevity or reliability with synthetic. The lab is neat, but does it really extend the life of an engine. Perhaps it’s just too new and nobody knows yet.

In short, until I see some actual data relating engine longevity to synthetic oil I can’t personally justify the price. 40 years without wearing out an engine even after 338,000 miles is good enough performance for me.

Nancy, true (there are some out there that say, synthetic, but they’re not) synthetic oil is excellent for new and older and old cars. I’ve been using it (Mobil 1) in my vehicles for over 2 decades with great results and saving lots of money on oil changes while providing the best engine protection for all my cars (one of my cars has almost 155,000 miles on it and Mobil 1 has been used in it from day one). Mobil even has a new synthetic oil, which is the most enviro friendly oil on the planet. But, why don’t you check it out for yourself at:

They’re not one of the richest companies on the planet for nothing.