Synthetic Versus Conventional: Which Motor Oil is Best?

Which motor oil is the best?

As the lubricant for the moving parts of your engine, motor oil is widely considered to be the most important fluid you can use. It prevents excessive engine wear and tear, which makes it vital to keep your car running. So it’s important to understand the different types of motor oil available and how to choose the best one for your vehicle, budget, and needs.

Conventional, synthetic, and blend

There are three main types of oil–conventional, synthetic and synthetic blend. Conventional oil is organic—it’s essentially refined crude oil that’s been pumped up from the ground. Synthetic oil is manufactured molecule by molecule, and because of that, synthetics have fewer imperfections in their chemical buildup than conventional does. Synthetic blends, or “semi-synthetics,” add synthetic additives to conventional oil and can be a nice compromise between the two. They’re less expensive but provide some of the performance enhancement you get from a synthetic.

And…synthetic wins?

In general, synthetic oil outperforms conventional oil on all counts:

  1. Synthetic oil works better in extreme temperatures from below freezing to above 100′ F. Conventional oil is highly reactive to temperatures.
  2. Because synthetics have superior lubrication (they’re more slippery) and create less sludge, so they give you better fuel economy, performance, and even a longer engine life.
  3. And best of all, synthetics don’t have to be changed as often. But make sure you meet warranty service mileage intervals regardless.

The only downside to synthetic oil is it costs more than the regular stuff–typically twice as much. That’s a big difference. But before you choose pennies over performance, crunch the numbers. With longer oil change intervals, the price difference might be a wash. However, if you don’t drive your car hard and/or in extreme conditions, and if you don’t tow heavy loads or supercharge your engine, and if you change your oil promptly on schedule, the price increase to switch from conventional oil to synthetic may not be worth it to you.

Keep in mind…

These three types of motor oil will work fine in your vehicle as long as they meet current American Petroleum Institute (API) certification and don’t go against the manufacturer’s recommendations. The only type of engine you should never use synthetic oil in is a rotary. Rotary engines have unique seals that are engineered for use with conventional oil only.

Pro Tip: Check that you’re not voiding your warranty by using the wrong oil. Many newer vehicles require that you use synthetic oil and some synthetics aren’t approved for certain diesel engines.

The final say

When buying oil for your car, the best thing you can do is to follow your manufacturer’s recommendations. So, check that owner’s manual! When you consider that the wrong oil can cause an engine to fail, it pays to take their suggestions seriously. If you have the option to choose between synthetic and conventional and still aren’t sure which to pick, try a synthetic blend. Still unsure? Consult a pro.

So where do you fall in the synthetic vs. conventional debate? Leave us a comment.


  1. Charles Ellis says:

    I agree using synthetic oil is best, but my vehicles are a 2003 Chevrolet Malibu with 125K miles & a 1998 Ford Windstar with 165K miles. I currently run high mileage oil in both. I have heard that running synthetic oil in high mileage vehicles is not good. What is your opinion for that?

    • I have read that older engines that have run conventional oil the entire time will have accumulated sludge on the oil gallery walls. Synthetic oils will cause sludge to be broken up and held in suspension. The problem arises when this collects in the filter and clogs it, causing a loss in protection of the rings, etc. if you do this you will need to do a filter change repeatedly at shorter intervals. So the benefits may not be there.

    • Hi Charles – Full Synthetic Oil should not be bad for any engine, at any mileage. It all meets or exceeds the API certification for your engine. This type of misconception may have stemmed from the 1970’s and early 1980’s when cork gaskets were primarily used in valve covers and oil pans. At that time, Synthetic Oil was somewhat new to the marketplace and vehicle owners started using the oil in their cars with 50+ thousand miles on them. The problem was that cork gaskets are much more porous than the rubber gaskets used in today’s vehicles and the synthetic oil was able to seep through the cracks in the cork gaskets. This caused “new” leaks on engines that had higher miles and thus the rumor was born.

      Today’s “High Mileage” motor oils are almost all Synthetic Blend motor oils. So chances are you are already using a Synthetic Blend oil right now. Stepping up to a Full Synthetic should not be an issue. Just be sure to use the recommended weight of oil and change your filter regularly (every 5k-7k miles or follow your owner’s manual). Even though Synthetic Oils can last up to 15k miles, your filter does not have the capacity to last that long. Putting a fresh filter on and topping off the oil is the key to making the most of your Synthetic Oil change.

    • You should not go back to an oil that does not have the chemistry of a high mileage oil,high mileage oil has seal swellers in it. To make seal larger to tighten up seals to slow down or prevent leak, once you use it it will swell the seals in the engine,using a different oil after high mileage oil could create problems, check out pat goss on you tube about high mileage oil.

  2. Jose Montes says:

    I want to know. If I choose syntetic oil, and after that. Can I use conventional for the next oil change ?

    • Jose, you won’t do any physical damage by going back to conventional for the next oil change, but we recommend staying with the synthetic. You’ll be able to increase the time between changes and keep the performance benefits going.


    Very useful information about motors oils.

  4. Does synthetic oil work better in older vehicles that “use” conventional oils? Do they “leak or burn” out as much?

  5. I ONLY run Mobile 1 full synthetic in my 1991 Mitsubishi 3000 gt. Im at 240.000 and going strong. Well worth the higher price.

  6. James Perkey says:

    I have a 2010 dodge Cummins I use 15w40 fully synthetic in & a 2013 Toyota sienna I use 0w20 fully synthetic in… Is there anything better I could use??

  7. Dave Mishem says:

    IMHO synthetic is only useful if it’s required by manufacturer (Honda etc), or if you perform all the work on the car yourself. Conventional oil with regular changes will last just fine to the 250,000-300,000 mile range these days. And almost all newer cars will be traded in or disposed of due to electrical or component issues, not engine or transmission failure. Simply put, if you’re the average person, engine life is not the limiting factor in your new car. That’s why the manufacturers can afford to give extremely generous drivetrain warranties.

    • Dave Mishem is right…… I’ve been working on automobiles for almost 50 years and I couldn’t add anything to his comment.

    • Agree electrical or component issues go before the engine but these are typically affordable to repair. That is why I say your automatic transmission is the weak link and when you want to say goodbye to your car.

  8. Jim Schmidt says:

    Good information. I do take issue with one technical point. Synthetic oil is not more slippery (unless it is specifically engineered to be so.) It is simply more durable making it more consistently slippery over a longer duty cycle. It is a common misperception that synthetics are more slippery, probably because this point is so difficult to explain.

  9. For more than thirty years I religiously used Mobil 1 in my 1970 Corvette until my Big Block came undone. Only then did I find out that Mobil 1 had removed the zinc from the oil causing engines from the early 70s and earlier needing the zinc for lubrication to self destruct. I now run 10w40 Brad-Penn oil with enough zinc to lubricate my LS5 Corvette.I will admit that Mobil 1 will keep the inside of your engine spotless and will work very well in new engines not the older ones.

    • Bill Johnson says:

      Who told you you need zinc for lubrication? I ran Mobile 1 in my 69 Charger R/ T and never had a problem. Stop listening to people who write in forums. Call the oil manufacturer and ask them if there is a problem using it. Look up 540 rat-tech facts, not myths

  10. I heard that switching back to conventional oil after synthetics can cause problems. Is that true ?

    • Switching back to conventional after using synthetics…..did it a few times as I experimented with different oils of the years…..never a problem…..same thing with blending….. add a quart of synthetic to conventional, just make sure it’s the same weight and specifications.

  11. Several years ago I went online to see what info was out there on the subject. Pretty much every thing I found was in line with these posts. The exception was that one source said that while the synthetic lasts generally about three x’s longer, the life of the additives doesn’t necessarily last much longer than the conventional oils additives. Anybody have any factual info on this?

  12. I drove a ’89 Beretta 2.8 V6 200,000 miles on conventional oil. I changed the oil every 3,000 miles. The same with a ’97 Bonneville 3.8. Neither used oil. I now have a 2003 Monte Carlo SS and run synthetic oil in it. At 100,000 miles it uses 2 quarts of oil between changes. No sign of a leak…

  13. Synthetic oils are the best!! I’ve never used anything else but the best; I feel that if you use the best, you’ll find the best performance in any vehicle!!….

  14. I dont recommend switching to synthetic in a high mileage motor, dino conventional oils got you that far switching to synthetic on a high mileage motor accomplishes NOTHING

  15. Ray Beiber says:

    I have a 2004 Caddy with a V8 Northstar engine. The Northstar engine had special oil rings allowing better lubrication of the cylinder walls thus extending motor life and obtaining 25 MPG. I have heard using synthetic oil can plug the oil ring holes causing excessive wear, more oil usage and reducing engine life. I beleive in the manufacturer’s recommendation of using conventional oil.

  16. Can you put zddp in the synthetics oil

    • Hi Mario – ZDDP is a zinc additive which is typically only used during engine break in and in older engines with flat tappet lifters/camshafts.

      But to answer your question, you can add it to any type of oil. Conventional, HM, Blend, Full Synthetic all are able to use it as an additive.

  17. I won’t put synthetic oil in any car unless synthetic oil has been used in it since it was new.

  18. We usually recommend a synthetic to customers who get an oil change in our shop, but it’s always up to them. Yiu know, I just read an article about what engine oil is made from at . This reminded me of that article!

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