Synthetic oil versus blend

[Merrie]

My husband changed the oil in our '04 Toyota Corolla which has 130k miles. I have been getting a high-mileage synthetic blend put in (previously we always went somewhere to have it done) but he bought full synthetic this time. We have been going about 5k miles on an oil change without problems. Was the full synthetic a good idea? Can we go longer between changes now? How do we figure that out? This car gets pretty frequent usage, between 15-30 miles a day commuting.

[Spork]

You're going to get a huge range of answers... just warning you...

My theory is: go full synthetic and you can easily do 1.5x the manufacturer recommended rating between changes.  (I think you can go more like 2x - 3x... and Mobil 1 does have a guaranteed 15,000mile oil if you really want to go there.)

I also think if you're going longer between changes, you have to also cough up and buy premium oil filters.  There are several out there: Wix, Purolater, etc.  They really do have more filtering element and have finer filter paper to catch more crap.

[paddedhat]

In the world of car enthusiasts there are lots of opinions on this subject, many of the contradicting. If I was in your situation, I would Google Blackstone labs. Get a sample kit from them, run the car to 5K, then take a sample while changing the oil. They will then do a detailed analysis of your used oil and tell you their scientific conclusion of the results. They may say that the engine is in great shape, and the oil will do just fine if you leave it in until 8k. As for synthetic verses blend, I always use Mobil 1 full synthetic. It's a few bucks more, but when purchased in the five qt. jug at Wal-Mart, the price difference isn't enough to justify saving a few bucks to downgrade to a blend or conventional oil, IMHO. I change our Honda every 5K and use a mid-grade Purolator filter.

BTW:  I am not in the same camp as spork on this. This is a lot of evidence that extended change intervals (10-15K) are coming back to bite owners and manufacturers. Manufacturers, in some cases, have been quietly changing requirements to much lower intervals, since it has led to issues with horribly expensive engine failures. It's your choice, but when it comes to a small engine, with fairly low oil capacity, there is no way in hell I would every let it go 10K before changing, regardless of the oil type or filter specs.

[NateC]

Manufacturers, in some cases, have been quietly changing requirements to much lower intervals, since it has led to issues with horribly expensive engine failures. It's your choice, but when it comes to a small engine, with fairly low oil capacity, there is no way in hell I would every let it go 10K before changing, regardless of the oil type or filter specs.

Can you provide a link or reference to support this?

I don't like the idea of extended drains (over 6500 miles) because you should be under your car more often to look over everything. I drive maybe 8000 miles a year and try to get under the car at least twice a year to catch things before they become a problem. Even if your motor oil lasted 15K, you should grease your chassis far more frequently.

[paddedhat]

Manufacturers, in some cases, have been quietly changing requirements to much lower intervals, since it has led to issues with horribly expensive engine failures. It's your choice, but when it comes to a small engine, with fairly low oil capacity, there is no way in hell I would every let it go 10K before changing, regardless of the oil type or filter specs.

Can you provide a link or reference to support this?

I don't like the idea of extended drains (over 6500 miles) because you should be under your car more often to look over everything. I drive maybe 8000 miles a year and try to get under the car at least twice a year to catch things before they become a problem. Even if your motor oil lasted 15K, you should grease your chassis far more frequently.

http://blog.modbargains.com/15000-mile-oil-change-myth/

One of many articles available with a Google search. The damage issue is also pretty well know by most decent mechanics who do engine work.

[NateC]

Manufacturers, in some cases, have been quietly changing requirements to much lower intervals, since it has led to issues with horribly expensive engine failures. It's your choice, but when it comes to a small engine, with fairly low oil capacity, there is no way in hell I would every let it go 10K before changing, regardless of the oil type or filter specs.

Can you provide a link or reference to support this?

I don't like the idea of extended drains (over 6500 miles) because you should be under your car more often to look over everything. I drive maybe 8000 miles a year and try to get under the car at least twice a year to catch things before they become a problem. Even if your motor oil lasted 15K, you should grease your chassis far more frequently.

http://blog.modbargains.com/15000-mile-oil-change-myth/

One of many articles available with a Google search. The damage issue is also pretty well know by most decent mechanics who do engine work.

I was interested in the manufacturer's recommendation specifically. Wouldn't there be a TSB if they changed the recommended schedule?

[paddedhat]

The linked article include nearly a million vehicles recalled by GM to recalibrate the oil condition monitors and shorten intervals, and letters sent to BMW and Mini owners to reduce intervals from 15K to 10K. A bit of time searching reveals similar moves by Toyota, Ford and others. As for TSBs, a bit of a smoking gun, eh?  Just guessing, but what would you think corporate legal would say to a TSB that says, "hey, we were full of shit when we told millions of customers to go as far as 15K, since it's destroying our engines and leaving them with massive repairs bills to our cars that are conveniently out of warranty"  Remember these are the some of the same bastards that saved less than a buck each on defective  ignition switches that have killed dozens of people so far, I doubt they are looking for a way to spend billions to deal with issues like this.
It currently cost me about a 1/3rd of a cent per mile to change with full synthetic and a decent filter every 5K, as opposed to every 10K. I have read and heard countless reasons why I should be doing everything from following the vehicles "maintenance minder" (which is currently recommending a change at 9K, or so) to buying magical oil, only sold by independent distributors and using their magical filters to get 15 or 20K intervals. Like you correctly point out, it doesn't add up, and getting under the thing every 5-6K for a good look around is a good routine to get into.

[The Beacon]

Manufacturers, in some cases, have been quietly changing requirements to much lower intervals, since it has led to issues with horribly expensive engine failures. It's your choice, but when it comes to a small engine, with fairly low oil capacity, there is no way in hell I would every let it go 10K before changing, regardless of the oil type or filter specs.

Can you provide a link or reference to support this?

I don't like the idea of extended drains (over 6500 miles) because you should be under your car more often to look over everything. I drive maybe 8000 miles a year and try to get under the car at least twice a year to catch things before they become a problem. Even if your motor oil lasted 15K, you should grease your chassis far more frequently.

http://blog.modbargains.com/15000-mile-oil-change-myth/

One of many articles available with a Google search. The damage issue is also pretty well know by most decent mechanics who do engine work.

The post used a 60k OCI example to support his "15000 OCI is bad" argument. I just do not buy it.  It is a good idea to do an oil analysis if you are really worried. Otherwise, 10k is safe with full synthetic and 5k with dino

[MikeBear]

I do NOT recommend that you go greater than around 5 - 6k max, on an '04 Corolla, even with synthetic! It can end up causing a problem with the oil crystalizing. That can eventually fuse the oil rings to the pistons, and it'll start blowing-by oil. Those engines get real hot combustion, which can make it real hard to see if any is blowing out the exhaust.

I've had it happen to me, (I went to 7.5k with Mobil-1 and ended up ruining my engine) and I'll never go beyond 5k on any car I own anymore. Even IF the manufacturer says you can. Toyota covers up issues like this, and they are real good at hiding it.

Also, if you stretch the oil changes out, please take it upon yourself to check the oil a few times after you get over about 4k, to make sure you don't need to add any. At least until you figure out how long you can safely go between changes. My son's Corolla ran over 200 miles with next to NO oil in it, and it didn't seize up. That doesn't mean it didn't cause damage though.

Oil changes are cheaper than a replacement engine...

[paddedhat]

The post used a 60k OCI example to support his "15000 OCI is bad" argument. I just do not buy it.  It is a good idea to do an oil analysis if you are really worried. Otherwise, 10k is safe with full synthetic and 5k with dino

The 60K pics. are part of an article with lots of other documentation regarding extending to 15K and why it is something that manufacturers are walking back from. Your blanket statement regarding 10K intervals is far too broad, and can lead to failures in some situations. As discussed in another post on this topic, I owned one of the worst engines Chrysler ever built, the Daimler/Chrysler 2.7 V6. This vehicle is now on it's third owner, was used as a daily loaner in a shop for years, and has over 300K reliable miles on it. It gets an oil change every 5K, or less. The same repair shop that owns the car has customers that didn't get to 80K on this motor with extended changes. My lawyer managed to kill a 4 cyl. Camry after a handful of extended intervals. The car had 60K on it, and smoked like a worn out diesel.

It is of particular importance to members here to understand the concept of "SEVERE DUTY" and how it applies to you. Most manufacturers have, or had, recommendations to greatly shorten OCIs when the vehicle is used for short trip and stop and go traffic, as opposed to longer, high speed use, where the engine has a chance to get hot and vaporize condensation and even coolant intrusion. These severe duty recommendations often fit the profile of a typical MMM driver, and the recommendations are often for 3-3.5K change intervals. With the advent of maintenance minders, or computerized evaluations of oil condition this is no longer as common. The problem with most of these oil life monitors are that they are using programs to monitor everything but the actual oil. They look at all the inputs provided and provide a "best guess" as to the condition of the oil. They do not account for things like coolant intrusion, particulates, high bypass at the air filter, etc.... All of which lead to oil contamination.

So, you're a hardcore MMMer,  driving a twenty year old Honda, or Toyota that could last you another ten years? You take the advice of the online experts and decide that 10K is fine with synthetic. The fact that you are getting a bit of blow-by from the rings, a bit of coolant past a tired gasket, or have a POS air filter that is letting a ton of particulates in didn't matter when you changes the oil every 5K, or so, but your just trying to not waste money on the car, so you decide to go twice as far. A year into this program and the car is starting to smoke, or need oil a lot more frequently. You do the 10K change. A few month go by and it's now taking a qt. a week, and it won't pass an emissions test.  Now the car needs a motor that costs more than the car is worth. How much did you really save?

[The Beacon]

The post used a 60k OCI example to support his "15000 OCI is bad" argument. I just do not buy it.  It is a good idea to do an oil analysis if you are really worried. Otherwise, 10k is safe with full synthetic and 5k with dino

The 60K pics. are part of an article with lots of other documentation regarding extending to 15K and why it is something that manufacturers are walking back from. Your blanket statement regarding 10K intervals is far too broad, and can lead to failures in some situations. As discussed in another post on this topic, I owned one of the worst engines Chrysler ever built, the Daimler/Chrysler 2.7 V6. This vehicle is now on it's third owner, was used as a daily loaner in a shop for years, and has over 300K reliable miles on it. It gets an oil change every 5K, or less. The same repair shop that owns the car has customers that didn't get to 80K on this motor with extended changes. My lawyer managed to kill a 4 cyl. Camry after a handful of extended intervals. The car had 60K on it, and smoked like a worn out diesel.

It is of particular importance to members here to understand the concept of "SEVERE DUTY" and how it applies to you. Most manufacturers have, or had, recommendations to greatly shorten OCIs when the vehicle is used for short trip and stop and go traffic, as opposed to longer, high speed use, where the engine has a chance to get hot and vaporize condensation and even coolant intrusion. These severe duty recommendations often fit the profile of a typical MMM driver, and the recommendations are often for 3-3.5K change intervals. With the advent of maintenance minders, or computerized evaluations of oil condition this is no longer as common. The problem with most of these oil life monitors are that they are using programs to monitor everything but the actual oil. They look at all the inputs provided and provide a "best guess" as to the condition of the oil. They do not account for things like coolant intrusion, particulates, high bypass at the air filter, etc.... All of which lead to oil contamination.

So, you're a hardcore MMMer,  driving a twenty year old Honda, or Toyota that could last you another ten years? You take the advice of the online experts and decide that 10K is fine with synthetic. The fact that you are getting a bit of blow-by from the rings, a bit of coolant past a tired gasket, or have a POS air filter that is letting a ton of particulates in didn't matter when you changes the oil every 5K, or so, but your just trying to not waste money on the car, so you decide to go twice as far. A year into this program and the car is starting to smoke, or need oil a lot more frequently. You do the 10K change. A few month go by and it's now taking a qt. a week, and it won't pass an emissions test.  Now the car needs a motor that costs more than the car is worth. How much did you really save?

I do not think my statement is too broad since it will cover most cases. I would never use any anecdotes to support any arguments because they are statistically invalid.

"SEVERE DUTY"  or "Normal" is common sense and stated clearly in the manual. I presume most people will follow that. And a lot of people do not have "SEVERE DUTY" if it is just daily commute.

Anyways, you do whatever you think is right. I trust my my manufacturer's manual over any internet experts. 

[paddedhat]

Statistically validity doesn't mean shit if you just trashed a motor. At that point there is little comfort in YOUR OPINION that the statistical majority of then will perform acceptably if done at 10K. As for severe duty, oddly enough there seemed to be more and more mentions in the automotive media regarding this topic, and the fact that far more drivers should be following that schedule. It is unusually important to members here, since it applies to many who attempt to use their vehicles very little, and do not commute with them. As for reading the manual, great idea, if the average person would even bother. That said, many manufacturers do not even mention various duty schedules in manuals anymore, as they rely on their magical oil monitor to tell the owner how much theoretical "oil life" remains.

[The Beacon]

Statistically validity doesn't mean shit if you just trashed a motor.

The problem with that statement above is that most people have not trashed their motors at 10k OCI  with full synthetic. That is why "Statistical validity means a lot in proving anything". Not using one or 2 out liers to prove anything is common sense. Learn some math. It helps a lot.

Your argument is like "healthy diet does not mean anything if you already have cancer". It seems plausible on the surface. After all, you are going to die. But it really is as weak as it can get because most people do not have cancer.
 
"if you just trashed a motor/already have caner." is an assumption not a conclusion.  Why would anyone use an assumption to prove anything?  Logic of reasoning 101 please.

Did you eve read OP's post?  "This car gets pretty frequent usage, between 15-30 miles a day commuting."

[cjottawa]

...We have been going about 5k miles on an oil change without problems. Was the full synthetic a good idea? Can we go longer between changes now? How do we figure that out? This car gets pretty frequent usage, between 15-30 miles a day commuting.

First, you don't know if an extended oil drain cycle is "without problems." The problem would be cumulative wear which is only noticeable as your engine, over time, looses compression and eventually needs a rebuild. Reducing your oil change interval and/or using a high quality full synthetic will reduce wear.

5,000km with a full synthetic, all things being equal, is going to cause less wear than using a non-synthetic or extending the drain interval.

FYI, I've had this explained to me by both aircraft engine mechanics and factory trained car mechanics. I'm convinced that synthetic oils do make a difference and will help the longevity of your engine.

I've been told by mechanics that any oil - conventional or synthetic - lubricates well the day you put it in your car. Over time, both will suffer some breakdown but synthetic is much more resistant, ergo it's effective at lubricating over more kilometers.

Full synthetic oils have a much higher flash point than conventional mineral oils. The temperatures oil is exposed to in the cylinder walls are higher than the flash point of conventional and (IIRC) lower than that of good synthetics.

It's time and exposure to heat in the cylinder walls that breaks conventional oil down faster leading to sludge that wears parts down. A full synthetic won't degrade as quickly so there's less wear-inducing sludge throughout the life of the oil.

I won't get into what constitutes a reasonable oil change interval other than saying 5,000km with a full synthetic is a very safe schedule and that oil analysis as suggested by "paddedhat" is going to give you hard data as to the state of your engine and oil so you can make an informed decision on future oil change intervals.

Putting in a plug for the stuff my mechanic uses: "Liqui-Moly" fully synthetic 5w-40, imported from Germany. (careful: they sell semi-synth and conventional in the US and Canada that's labeled "with synthetic technology" - you want the one labeled "fully synthetic")

[Spork]

You're going to get a huge range of answers... just warning you...

Was I right or what?

I'm old.  I've generally had more cars than makes sense.  I've kept them long times and driven them many miles.  I've always done 1.5x the manufacturer's recommendation.  If there was a warranty involved, I wouldn't do that: I'd match it -- but I don't generally have new cars.  I've never had any issues.  But that's extremely anecdotal and really doesn't mean squat.

What I'd add to this mess (beyond, "just use your best judgment") is: if you're not going to go more than the manufacturer's recommendation and you are not operating in extreme conditions, there probably isn't a real reason to use synthetic.  The whole purpose of using it is: it doesn't break down with heat and age.  It does, of course, pick up particulates and other contaminates -- and that's why you have to change it.  But extended and/or heavy use is the reason you'd use it.  If you don't, you might as well buy a high quality traditional oil.

[Syonyk]

Another thing to consider is a bypass filter (a low flow, high filtration setup that doesn't filter *all* the oil, just some of it - it can flow a lot less than a stock oil filter and clean the oil better in the process).

Unfortunately, that makes the most sense if you're putting absurd numbers of miles on your vehicle.  Say, a semi.  Or delivering RVs with your truck.  Or something like that.

... I still want one for my truck. :/  Even though I don't put many miles on it and change the oil annually whether it needs it or not.

[Jack]

FWIW, I'm doing the following:

• 1998 VW Beetle TDI (200K miles): Shell Rotella T-6 synthetic + good filter; 10000 mile interval
• 1996 Ford Ranger 2.3L (200K miles): Valvoline Nextgen synthetic + good filter; 5000 mile interval
• 1990 Mazda Miata (80K miles): Valvoline synthetic + good filter; 3000* mile interval

The TDI gets such a long OCI because that's what VW recommends and the gurus at TDIClub.com say it's okay.

The Ranger is designed for conventional oil and a 3000-mile interval; I could probably push it more (maybe even up to 10K) but am playing it safe.

The Miata has had full synthetic and 3000-mile oil changes by its previous owner. On one hand, I'd be inclined to extend to 5000 miles just because changing it frequently is a pain in the ass. On the other hand, I autocross it and otherwise drive it "vigorously," so changing it earlier makes sense. On the third hand, today was the first time I changed it since buying it, and the oil came out so dark that I'm wondering if I accidentally left it in there for 6K instead of 3K. (I bought it at 81.5K on the odo and assumed the 81K oil change was done, but maybe I was wrong.) If it was 6K then I'd definitely not let it go that long in the future, and if it was 3K then I really won't extend the interval at all. I'll have to see how it looks at 87K, and get a used oil analysis next time I change it.

Full synthetic oils have a much higher flash point than conventional mineral oils. The temperatures oil is exposed to in the cylinder walls are higher than the flash point of conventional and (IIRC) lower than that of good synthetics.

For this reason, one should never even think about using less than a full-synthetic oil in any car with a turbocharger, because the oil gets really hot lubricating a 100,000+ RPM bearing attached to a turbine that's being driven by hot exhaust gases.

[thurston howell iv]

OP: As you have seen, there are a number of opinions on oil. When I was younger (think 24), I was of the mentality that oil should be changed every month regardless of miles (I was apparently bored and needed something to do). I never had any engine related issues.

With my current fleet of cars I cannot change the oil every month but, most all the cars get full synthetic (one gets regular dino) and they stay on a 3 month schedule (unless I have a long trip- then it's sooner)  The oil is the car's life blood. It's $21 for a jug of Castrol or Mobil One full synthetic (decent quality stuff) at walmart- filters are cheap too. It is foolish to drag out intervals in order to save a few bucks a year. An engine is much more expensive... My DD's have 243k and 180k respectively. Still going strong.  Using Synthetic Blend feels like buying mid-grade 89 octane fuel- a waste of money...

[Colgate_Toothpaste]

Oil debates get crazy- if you want to see mayhem, go on any drag racing forum and ask about detergent-free break-in oils. 

Anyways, you'll be fine with synthetic.  I wouldn't go more than 5k unless you have an oil like Amsoil XL that is rated for 10k miles.

As for performance differences, for every test showing gain there is another disproving the last. 

The best general synthetic (cost, availability, wear protection) is Shell Rotella (diesel oil).  The best bang for the buck is Amsoil XL (only downside being availability). 

Check this study out:
http://www.amsoil.com/lit/g3115.pdf

[JLee]

Oil debates get crazy- if you want to see mayhem, go on any drag racing forum and ask about detergent-free break-in oils. 

Anyways, you'll be fine with synthetic.  I wouldn't go more than 5k unless you have an oil like Amsoil XL that is rated for 10k miles.

As for performance differences, for every test showing gain there is another disproving the last. 

The best general synthetic (cost, availability, wear protection) is Shell Rotella (diesel oil).  The best bang for the buck is Amsoil XL (only downside being availability). 

Check this study out:
http://www.amsoil.com/lit/g3115.pdf

You can order Amsoil stuff direct and it'll get shipped to your house. For $15 you can get a preferred customer discount and buy at wholesale (or you can find a dealer - they're everywhere).

The only accurate way to tell how your oil is doing is to send a sample out for analysis.

[Jack]

The best general synthetic (cost, availability, wear protection) is Shell Rotella (diesel oil).

"Shell Rotella" is a 15W-40 conventional (not synthetic) oil that comes in a white jug.

"Shell Rotella T6" is a 5W-40 synthetic oil that comes in a blue jug.

They are not interchangeable. Make sure you get the T6.

[Merrie]

Thanks everyone. I think I will look into getting a sample analyzed a bit down the line. I am not really that knowledgeable about this stuff, so seemingly basic things in this thread like that regular oil breaks down and synthetic oil does not were helpful to me. As was the idea that "just because the engine has been fine so far doesn't mean it's going to stay fine". Also the "dinosaurs" reference made the "oil is a fossil fuel" thing click in my brain. Doh. I will discuss all of this with my husband. He was under the impression that synthetic oil=fewer oil changes, and I thought it was controversial, but my only reference was a 20-year-old Tightwad Gazette article.

[JLee]

Thanks everyone. I think I will look into getting a sample analyzed a bit down the line. I am not really that knowledgeable about this stuff, so seemingly basic things in this thread like that regular oil breaks down and synthetic oil does not were helpful to me. As was the idea that "just because the engine has been fine so far doesn't mean it's going to stay fine". Also the "dinosaurs" reference made the "oil is a fossil fuel" thing click in my brain. Doh. I will discuss all of this with my husband. He was under the impression that synthetic oil=fewer oil changes, and I thought it was controversial, but my only reference was a 20-year-old Tightwad Gazette article.

You generally can do extended drain intervals with a quality synthetic oil, but the only way to truly tell how your oil is doing is to have it analyzed by a lab. A lot of people think they can tell if their oil "looks clean" but that isn't the case.

[Jack]

Also the "dinosaurs" reference made the "oil is a fossil fuel" thing click in my brain.

Conventional motor oil is only a fossil fuel if you're using it in a Diesel engine... and even then, something's probably wrong.

Otherwise, it's just a fossil "product." ; )

(If you have an old indirect-injection Diesel engine that you don't care about, and you also don't care about emissions, then it could actually run on waste motor oil used as a fuel. It's a nasty business though, and the metal particles will wear out the injection system faster.)

A lot of people think they can tell if their oil "looks clean" but that isn't the case.

This is an important point: the oil in my diesel car turns opaque black after only a few miles, but is still good to go for thousands more. Conversely, it's entirely possible for an oil to "look" almost new but have all the additives gone.

[BlueMR2]

"SEVERE DUTY"  or "Normal" is common sense and stated clearly in the manual. I presume most people will follow that. And a lot of people do not have "SEVERE DUTY" if it is just daily commute.

If you read the "severe duty" requirements you may be interested to see that it actually describes the typical commute...  "Normal" duty is long expressway trips, like vacations or really LOOOONG commutes.

[cjottawa]

"SEVERE DUTY"  or "Normal" is common sense and stated clearly in the manual. I presume most people will follow that. And a lot of people do not have "SEVERE DUTY" if it is just daily commute.

If you read the "severe duty" requirements you may be interested to see that it actually describes the typical commute...  "Normal" duty is long expressway trips, like vacations or really LOOOONG commutes.

BINGO.

My mechanic made exactly that point with me last year. Typical city stop-and-go, short commutes, non-highway driving - basically, a high number of cold-hot-cold cycles when the car doesn't have a chance to come up to optimal temperature is "severe."

In Canada, he argues, all of our driving is severe and the reduced maintenance intervals suggested in the owner's manuals should be used. (check 'em out - they're significantly different from the "normal" intervals)

[Colgate_Toothpaste]

The best general synthetic (cost, availability, wear protection) is Shell Rotella (diesel oil).

"Shell Rotella" is a 15W-40 conventional (not synthetic) oil that comes in a white jug.

"Shell Rotella T6" is a 5W-40 synthetic oil that comes in a blue jug.

They are not interchangeable. Make sure you get the T6.

+1 on that!

Oil debates get crazy- if you want to see mayhem, go on any drag racing forum and ask about detergent-free break-in oils. 

Anyways, you'll be fine with synthetic.  I wouldn't go more than 5k unless you have an oil like Amsoil XL that is rated for 10k miles.

As for performance differences, for every test showing gain there is another disproving the last. 

The best general synthetic (cost, availability, wear protection) is Shell Rotella (diesel oil).  The best bang for the buck is Amsoil XL (only downside being availability). 

Check this study out:
http://www.amsoil.com/lit/g3115.pdf

You can order Amsoil stuff direct and it'll get shipped to your house. For $15 you can get a preferred customer discount and buy at wholesale (or you can find a dealer - they're everywhere).

The only accurate way to tell how your oil is doing is to send a sample out for analysis.

+1.  You need to stock up if you do it that way (which is how I've done it).  If you want to buy local to avoid the preferred customer fee, it can be hard to find.

Amsoil is good stuff.  I went from 23mpg to 26mpg average when I switched from Pennzoil synthetic to Amsoil XL.