When buying motor oil, I typically choose whichever synthetic is currently on sale, taking care to use the correct viscosity for my particular car, and I stick with a familiar brand. If nothing is on sale, I’d go with Mobil 1 because it’s a reliable brand with a solid track record for providing excellent engine protection, and it’s on the tip of the tongue of every expert I spoke with.
But above all else, make sure you change your oil regularly, following the recommendations in your owner’s manual. The greatest oil in the world eventually fills with contaminants and breaks down from heat and friction. Failure to change the oil in your engine regularly will eventually cause serious damage (and void your warranty).
Motor oil is a tough subject because of the complex chemistry involved and the difficulty seeing the actual effects of different formulations or brands. People can be pretty passionate about their favorite brands, too. To solve this puzzle, I threw out everything I thought I knew about oil and spent two weeks thinking about little else. I read reviews and evaluations from magazines and consumer groups, then consulted with techs at oil manufacturers and labs that perform oil analysis. I talked to mechanics who see the effects of oil use and misuse on every possible make and model of car. I even spoke to veteran race engine builder Ron Hutter.
Blackstone Laboratories has been testing motor oil using inductive coupled plasma spectrometry since 1985. I asked company president Ryan Stark if he’d seen any oils that performed consistently better or worse, based on his test results. “No. If you stick with a name brand oil, you really can’t go wrong. If you did a side by side test between two brands you might see a 1 or 2 parts per million difference in the metals in the results.”
Royal Purple manufactures what they call “super-premium motor oils for consumer use.” From the company’s origins in the 1980s as a developer of industrial lubricants, they expanded into racing oil and eventually consumer motor oil in 2003. Jim Morrissey, a junior automotive technical support engineer with Royal Purple, was candid about the challenges in evaluating motor oils when I asked him how a consumer could choose between two oils on a store shelf. “That’s one of the difficulties, actually. There are ways of determining a minimum standard, like the API certification, but when you’re dealing with a premium product, there really is no third party available to evaluate the product. Sometimes a magazine or TV show will do a side-by-side analysis, but it’s pretty much up to the consumer. Determining which is ‘the best’ can be nebulous. It depends what you’re looking for.”
Even Valvoline’s own FAQ for their synthetic SynPower has a hard time coming up with any appreciable differences between brands: “How does Valvoline SynPower compare to Mobil1 and Amsoil? Valvoline’s SynPower synthetic motor oils meet and exceed the same specifications as these two products.” Not exactly a ringing endorsement.
I spoke with Bob Gugino, owner of Bison Automotive in Kenmore, NY (he’s the guy I take my car to when it’s a problem I can’t fix myself). Bob’s been a mechanic for 35 years. He told me, “As far as brand names, Valvoline, Mobil, Castrol, there’s not a whole lot of difference between them. They all make a lot of claims, that their oil is better at this or that, but they all have to meet a certain spec.”
I also spoke with Kevin Knox, an auto technician at Mullane Motors in Lockport, NY with 30 years of experience. Because he works at a dealership that also sells used cars, Knox has been under the hood of many different makes and models of cars. “A lot of people have preferences, I don’t know if one brand is superior. I look at the requirements of the vehicle.”
Even on internet forums dedicated to motor oil, where people can get downright religious about their favorite brands, you’ll find plenty of “oil is oil” advice. A user named SteveSRT8 at the Bob is the Oil Guy forum said in 2012, “Seriously, we run a fleet with all 6.0 [liter engines] and a few 5.3s and they run nearly forever. Our secret? Pick whatever synthetic is on sale and change when the OLM says to. Pretty simple. And we have as severe a duty cycle as anything in the entire world.”
First, let me tell you something about oil.
All motor oils sold in the U.S. are tested by the American Petroleum Institute (API). If the oil meets certain minimum qualifications, the manufacturer can place the API star logo on the package. I’m not sure if it’s even possible to find non-API approved oil on store shelves. Also check the API “donut” that appears next to the star. It should have the letters “SM” on it, designating the latest API oil category specification, designed for modern engines. Again, it’s actually difficult to find oil that doesn’t carry the SM designation—a few specialty manufacturers produce oils for classic cars that have oil requirements not met by modern formulations, so you may occasionally come across “SF” oil or another designation.
If you keep an eye on Amazon for sales, watch for rebates at manufacturer websites, or spot a sale at your local auto parts store or Wal-Mart, you can get popular oil brands for prices as low as $3 per quart for conventional oil and under $10 per quart for synthetics.
If you’re looking for oil that meets some kind of performance test that sets a higher bar than the API logo, you might look for General Motors’ Dexos certification. An oil carrying the Dexos logo meets a more stringent set of requirements. However, note that GM requires oil manufacturers to pay a licensing fee to carry the Dexos logo. Not all manufacturers pay for the licensing. For instance, in a 2011 interview with Edmunds, a Valvoline representative said, “Our SynPower 5W-20, 5W-30 and DuraBlend 5W-30 went through all the Dexos testing and passed all the requirements. But we felt that carrying the Dexos name was not providing the consumer with any value.”
Why is Mobil 1 my pick, price notwithstanding? I asked Philip Reed, senior consumer advice editor for Edmunds.com, if there are appreciable differences between brands of motor oil. He said, “Keep in mind that most conventional oils are now using some percentage of synthetic. So the line between synthetic and non-synthetic is becoming blurred. Also keep in mind that oil chemistry in all oils is vastly improved in recent years. So if you stick with the name brands, you can’t go too far wrong…In most cases we just tell people to follow the guidelines in the owner’s manual. However, as cars get older the manual is less useful and the maintenance becomes even more important. This doesn’t mean more frequent oil changes but perhaps checking oil level more often. With that in mind, I’d have to say that Mobil seems most active in offering a wide range of oils for a range of cars of different ages.”
Mobil 1 holds a 4.4 out of five aggregate rating at Amazon, with 24 5-star reviews out of 34 total. While it’s difficult for the end user to really see the difference motor oil makes, reviewers tell some convincing tales of trouble free long-term use, which is what you really want out of a motor oil. Reviewer loustorm says, “I used to work at Aberdeen Proving Ground where, among other things, Army vehicles are tested. I learned that Mobil 1 was given a top rating. That’s all I use now.” Steven E. Snyder tells the tale of a Camaro filled with Mobil 1 that drove for several weeks with a faulty oil pump, concluding, “Even with little/no oil pump the car never locked up. Mobil 1 isn’t half-bad.”
Few other oils have the robust record of Amazon reviews that Mobil 1 enjoys. Valvoline Synpower 5W-40 has a 4.5 star average on 28 total reviews, which is certainly on par with Mobil 1. That particular formulation seems to find favor with owners of European-built or designed engines. “I have been using this oil in both of my Audis for several years and have put on thousands of miles with no engine lubrication issues. My older A4 has over 250,000 miles and still runs strong with only slight oil consumption between 5000 mile oil changes. My newer A4 does not use a drop between changes at 5000 miles. I have been very pleased with this oil and would recommend it to anyone that requires a 5W-40 for their Euro built vehicle,” said khubbard1.8T in 2012.
Royal Purple 5W-30 also has a 4.5 average on 87 reviews, but many of them parrot marketing hype or make ridiculous claims, like one reviewer who swears the oil caused his Mini Cooper to do a burnout. There are also a lot of reviews that acknowledge that Royal Purple is a fine synthetic oil, but seem put off by the higher price and marketing hype (note that, as I write this, Royal Purple is actually slightly cheaper than Mobil 1 at Amazon, but the prices shift frequently, not even counting sales and rebates). User trarmour is typical: “I have previously been using Mobil 1 in all of my vehicles and boats. Royal Purple claims of ‘feel the performance’ as well as improved mileage and more horse power. I didn’t receive any of that! I’m a certified GM technician and this is good oil however it is ‘just another synthetic.’ It’s not the ‘magical mystery oil’ Royal Purple claims. Not worth the additional cost in my opinion.”
Mobil 1 is used as the factory fill engine oil for all Chevrolet Corvettes, some Camaros, all Mercedes AMG cars, all cars made by Porsche, and specific models made by Holden, Acura, Nissan, Lexus, McLaren and others. That information certainly should be taken with a grain of salt—factory fill agreements can be as much the result of business partnerships and co-branding as oil performance. That still leaves the fact that Porsche trusts Mobil 1 enough to put it in all of their cars. Of course, each oil manufacturer has similar endorsements. Castrol is used as the factory fill by BMW, for example.
Sean Hixson, a public relations supervisor for Mobil 1, provided a few examples of Mobil 1 holding up under extreme conditions. “In a controlled wear protection test using a 2010 Honda Accord LX 4-cylinder, after 105,000 miles with 15,000-mile oil change intervals using Mobil 1 advanced fully synthetic oil, most engine parts were still within new engine tolerances. In a high-performance Chevrolet Camaro SS, our engineers tested Mobil 1 synthetic oil in the Camaro’s V-8 running at 25,000 mile oil change intervals—two to three times longer than recommended by Chevrolet—and found there was excellent engine cleanliness and no noticeable engine wear.”
Castrol claims superiority in a number of categories, based on their own internal testing, noting in one promotional video, “Castrol Edge with Syntec Power technology 5W-30 was proven stronger based on Castrol’s extreme test of maximum torque, strength and endurance versus Mobil 1 5W-30.” In another video, Castrol engineers extoll the virtues of their proprietary testing: “It’s been tested in some very specific and demanding tests that we have designed, such as the fluid strength test and the maximum endurance test. We have superior performance in the industry tests, superior performance in the OEM tests, but we will even invent tests that go beyond anything that’s looked at, and we will do well in our own proprietary tests.”
Pennzoil emphasizes their synthetic oil’s ability to reduce piston deposits, citing their performance in the American Society for Testing and Materials (ASTM) Piston Deposit Test. “Actual advantage over competition: Pennzoil Platinum keeps pistons up to 8% cleaner than Mobil 1; up to 17% cleaner than Valvoline SynPower; and up to 20% cleaner than Castrol Edge with Syntec.” Of course, reducing piston deposits is only one element of an oil’s performance.
The fact that every oil manufacturer can make these claims underscores the overall quality you’ll find in modern oils regardless of brand. While I think Mobil 1 is a safe choice to fall back on, if you can find another established brand of synthetic oil at a cheaper price, it will work just as well. If that seems like a pretty weak endorsement of Mobil 1 as the “best” motor oil, that’s intentional.
The array of oil varieties looks bewildering at first, but breaking down the decision into steps makes it a lot more manageable. First you need to know what viscosity is appropriate for your car. That’s the “5W-30” number you’ll see on the oil bottle. The two numbers refer to the oil’s viscosity properties during a cold start (the W stands for “winter”) and at high operating temperatures. Luckily, you don’t need to understand those numbers in any way. Just buy whatever your owner’s manual tells you to buy. It will clearly indicate what viscosity is required for your particular engine. If you’ve misplaced your owner’s manual, you can probably find it online.
The next decision is whether to buy conventional or synthetic oil. The owner’s manual might help out here, too—some cars require synthetic oil, or require an oil viscosity that only comes in synthetic oils (like 0W-20). If the manual doesn’t demand synthetic, you still might want to use a synthetic oil under certain circumstances:
Let’s say you’re on the fence about whether you should use conventional or synthetic oil. What’s the difference? Conventional oil is made from petroleum that comes out of the ground and is refined until it has the appropriate qualities for a motor oil. Various additives, like detergents, viscosity index improvers, and rust inhibitors, are then mixed in. Synthetic oils are built from designer molecules (which are still derived from petrochemicals) to have the exact qualities the manufacturer wants. They’re mixed with additives too.
Amazon’s product description, which they include for all synthetic oils, actually does a very good job of explaining the differences: “This oil is a full synthetic oil, meaning crude oil is not used in making it. Synthetic oil can be used in vehicle engines instead of motor oils refined from crude oil, and often provides superior mechanical performance over traditional motor oil, including increased gas mileage and reduced engine wear at extreme temperatures. Its complex method of production means it can often cost more than conventional motor oil.”
The base stocks that oils are made from are divided into groups, so you may hear gearheads talking about “Group IV vs. Group V synthetics,” which is based on whether the oil is derived from polyalphaolefins (PAO) or esters. Esters (Group V) are considered “better,” but for the end user, you’re more interested in how the final oil product performs than what base stocks were used. Oil manufacturers tend to not reveal exactly what combination of base oils were used to create their synthetic oils, so it’s difficult to base your purchase on this factor.
When I started researching this article, I figured synthetic oils were all marketing hype, and you could get by on conventional stuff. There certainly is plenty of marketing hype to go around in the motor oil business. But there is consensus that synthetics do offer better protection. The more extreme the conditions that the engine runs under, or the tighter the tolerances on that engine, the more a synthetic oil is going to shine.
In terms of raw numbers, synthetic oils hold a few advantages over conventional oils. According to Marlan Davis of Car Craft, a synthetic oil will still flow at temperatures more than 20 degrees Fahrenheit colder than the point where a conventional oil becomes too cold to lubricate the engine at startup.
Mike Allen, senior editor at Popular Mechanics, summarized the synthetic versus conventional debate in a 2007 article. “Some high-performance and high-end cars come factory filled with synthetic, and you should stick with it. If you live where it gets really frigid in the winter, you might be better off with a synthetic for its superior cold-weather starting. If you tow a trailer and your oil temperature is consistently above 200 F, you should use a synthetic oil and install an auxiliary oil cooler…If your driving cycle or your vehicle is more average, you probably can drive your car well past 200,000 miles without needing major engine work by using the proper grade of conventional mineral oil and appropriate change intervals.”
The final word on when to use synthetic oil comes from Ron Hutter. Hutter has been building racing engines for NHRA pro stocks and NASCAR modifieds since the 1970s, and built the engines that powered Dale Earnhardt, Jr. to a pair of Busch (now Nationwide) Series championships in 1998 and 1999. “Well, my regular car is a ’98 Cadillac with over 90,000 miles on it,” he told me. “I’m not too particular about what I put in that. But we have an ’06 Corvette, and we use synthetic oil in that.”
What a synthetic oil won’t do is give you any kind of noticeable performance boost at the gas pedal, despite manufacturer claims that they will. Yes, the superior lubricity and resistance to losing viscosity at high temperatures may give you a few extra horsepower. Under dynamometer testing, Car Craft found in 2009 that Mobil 1 0W-30 generated an extra 10 to 15 extra horsepower over conventional 10W-20 and 20W-50 conventional oils, at the cost of some reduced oil pressure.
So what are the benefits of synthetics? Bell Performance, which makes oil additives but not actual synthetic oil, explained in a 2011 article: “Synthetic oils tend to have better high and low-end viscosity performance in very hot and very cold weather. These oils are more resistant to wear and breakdown by oxidation (because they’re engineered to be so) and some synthetic oils can improve fuel economy. They are also more resistant to sludge formation because of this resistance to oxidation and they disperse sludge particles at least as well as regular oil.”
Perhaps the biggest benefit of synthetic oil is almost impossible to observe. Jim Morrissey from Royal Purple told me, “No one really does engine teardowns on a street car to see the wear the way racers do. So it’s really difficult to quantify the improvements you’ll see in terms of engine life and wear from using a synthetic oil.”
While synthetic oil can improve fuel economy, a 2012 Consumer Reports article observed that the small mileage boost (about 2 MPG) occurred mostly right after a cold start, and was offset by the higher cost of the oil. “But what’s behind so many makers of ordinary cars requiring expensive synthetic oil in the first place? SAE Fuels and Lubricants Council chairman James Linden says automakers can save between 0.5 and 1 percent on EPA fuel economy tests compared with 5W-20 motor oil. The tests are run starting with a cold engine, so the lower viscosity reduces friction until the engine warms up. Indeed, when Honda first presented us with details about the 2012 CR-V, company engineers emphasized that they had gained 2 mpg in EPA fuel economy ratings mainly by reducing friction in the engine and other mechanical components, not by introducing new technologies like direct fuel injection or continuously variable transmissions.”
Morrissey pointed out that, “More horsepower equates to better economy if you’re not running throttle wide open.” Royal Purple reports a 1-4 percent increase in horsepower, mainly based on reports from customers and engine builders (Morrissey was unaware of any internal company testing that would confirm those numbers).
Synthetic oils theoretically let you go longer in between oil changes, which the industry refers to as “drain intervals.” This could result in your buying less oil in the long run, balancing out the added cost of synthetic oil. However, I’d be careful here. The oil filter also plays a major role in determining your drain interval, so if your oil can go 10,000 miles, make sure the filter you use can go the distance as well.
If you have a newer car with an oil use monitoring system, change your oil when it tells you to (you may find yourself going 7,000 or more miles between drains). Monitoring systems track engine temperature, RPM and other factors, measuring how you actually use the engine. They’re considered very reliable. In 2010, Edmunds reported, “One GM car driven by Edmunds went 13,000 miles before the monitoring system indicated the need for an oil change. We sent a sample of that oil to a lab for analysis. The results showed the oil could have safely delivered at least another 2,000 miles of service.”
By the way, it’s safe to ignore your local oil change joint’s 3,000 mile recommendation. Edmunds also observed, “About the only ones that really need a 3,000-mile oil change are the quick-lube outlets and dealership service departments. In their internal industry communications, they’re frank about how oil changes bring in customers. ‘Many people…know when to have their oil changed but don’t pay that much attention to it,’ said an article in the National Oil and Lube News online newsletter. ‘Take advantage of that by using a window sticker system [and] customers will be making their way back to you in a few short months.'”
Almost all oil manufacturers attach a warranty to their product, guaranteeing that your engine won’t blow up because of a defect in the oil. Some of them require exclusive use of their brand (with the receipts to prove it), while others will warranty your engine within a given number of miles or months from when you put their oil in (again, with receipts as proof). Mobil 1’s warranty covers your engine within 15,000 miles of the oil change or the vehicles OEM recommended change interval, whichever is longer. That these warranties are so generous indicate how consistent and durable modern oils are, and how difficult it would be to prove than an engine failure was not due to a prior defect or other reasons unrelated to the oil.
Some brands have “extended life” synthetic oils that claim you can go 15,000 miles between oil changes. While there’s nothing wrong with using these oils, I’d still stick with owner’s manual/oil monitoring system recommendations for when to change your oil. I asked Bob Gugino about extended life oils, and his response couldn’t have been clearer: “I think that’s a joke. To go 15,000 miles between oil changes is not something you should be doing. You’re asking for trouble.”
Some oils are marketed as “high mileage” oils, specially formulated for older cars with a lot of miles on the engine. They may use detergents to clear away sludge and chemicals that swell old, dried out seals, theoretically preventing some oil leaks. Paul Weissler wrote about motor oil selection for Popular Mechanics in 2002, and he offered some technical details on what high-mileage oils seek to accomplish. “The higher-mileage oils are formulated with seal conditioners that flow into the pores of the seals to restore their shape and increase their flexibility. In most cases, rubber seals are designed to swell just enough to stop leaks. But the oil refiners pick their ‘reswelling’ ingredients carefully. Valvoline showed us the performance data of one good seal conditioner that swelled most seal materials, but actually reduced swelling of one type that tended to swell excessively from the ingredients found in some other engine oils…These higher-mileage oils also have somewhat higher viscosities. (Even if the numbers on the container don’t indicate it, there’s a fairly wide range for each viscosity rating and the higher-mileage oils sit at the top of each range.) They also may have more viscosity-index improvers in them. The result? They seal piston-to-cylinder clearances better, and won’t squeeze out as readily from the larger engine bearing clearances. They also may have a higher dose of antiwear additives to try to slow the wear process. If you have an older vehicle, all of these features may mean more to you than what you might get from a full synthetic, and at a fraction the price.”
Mechanics I talked to gave them mixed reviews, ranging from, “It’s a great product, I recommend it highly for cars with more than 75,000 miles. It keeps seals lubricated and supple and helps the piston rings stay sealed,” (Bob Gugino) to, “If you change your oil frequently, I see no reason to use high mileage oil,” (Kevin Knox). Ron Hutter said, “Even though I drive a high mileage car, I’ve never used one.” It’s worth noting that the higher viscosity of high-mileage oil means these formulations sometimes have trouble meeting the API rating for fuel efficiency. That means that these oils are the rare type you might find without the API logo on the bottle.
The bottom line here is that oil additives aren’t going to fix leaks. You’ll have to get those old seals replaced eventually. I wouldn’t pay a premium for high mileage oil, but if you have an old, abused engine and can get the oil at a good price, it won’t do any harm.
There are higher end synthetic oils such as Royal Purple, Motul, or Amsoil. They’re often highly touted on automotive forums, but I’ve yet to see anything other than anecdotal evidence that they actually perform significantly better than cheaper oils. They’re usually pretty expensive, but if you find them at a good sale price, they’ll get the job done.
You may see synthetic blend oil—these oils are literally conventional oils mixed with some amount of synthetic oil. They’re cheaper than full synthetics and are offered as a sort of compromise on price and performance. They’re slightly better than conventionals, not quite as good as full synthetics. Some auto enthusiasts even make their own blends, mixing conventionals with full synthetics in some ratio or another. No harm will come from mixing synthetic and conventional oils (or from switching back and forth between them from one oil change to the next). Some manufacturers even use blends for their “factory fill.” This is an option if you’re looking to save a little money—all the major oil makers have their own conventional/synthetic blends.
Full synthetics can cost a lot—three times as much as conventional oils. If you’re looking to save some money, you might consider using conventional oil. As long as your car doesn’t meet any of the criteria mentioned above for using synthetic oil, you can safely use conventional oil. I use conventional oil in my daily driver, a 2001 Toyota Echo with over 150,000 miles on it. If the car was brand new, I’d be using synthetics in it, but it’s been going strong for this long on conventional oil. “I don’t see a big advantage to using a synthetic oil [in a car that”s not high-performance],” Knox told me. “Frequent oil changes are the key. Keep the oil and filter changed regularly and there should be no problem, and you shouldn’t need synthetic oil.”
Which conventional oil is best? Valvoline NextGen performs as well as any conventional oil, costs as little or less, and is made with 50 percent recycled oil. Scientific American reported in 2009 that modern recycled oil is essentially identical to newly refined oil and doesn’t suffer from reduced performance. That added bit of environmental benefit gives NextGen (and other oils made with recycled oil) a slight edge over non-recycled oil. But again, any conventional oil that bears the API logos will get the job done.
Your best bet for motor oil is a synthetic like Mobil 1, Valvoline SynPower, or Castrol Edge, which you can get for a moderate price if you hunt for sales and rebates. If your car and your driving habits don’t demand the extra protection a synthetic oil delivers, you can save money by using a conventional oil. Above all else, follow the oil change schedule in your owner’s manual or as suggested by your car’s oil monitoring system.