Oil Change Interval ? When to Change your Oil

IGOTASTi

System Operator
Staff member
Another great article from @Texas1911. #oilchange #changeyouroil #intervals

For many car owners there’s a big misconception about oil change intervals. I will explain how to use your own logic to infer a proper oil change interval as well as debunk some of the myths surrounding when to change your oil. I will also discuss some of the differences between grades of oil, particularly synthetic versus conventional oil, and how they apply to oil changes. Lastly, I will talk about seasonality and when to short-change oil.

TL:DR – Give me the Cliff Notes!

  • Gasoline Passenger Cars – 5,000 to 7,000 Miles
  • Diesel Passenger Cars – 5,000 Miles
  • Sports Cars – 5,000 Miles
  • Hard Driven / Raced Sports Cars – Very Short, Especially Turbos and High Revving Engines
  • Gasoline Trucks (1 Ton or Less) – 7,000 Miles
  • Diesel Trucks – 10,000 Miles

While some specific cars recommend very long intervals, this is not a great idea without a very high quality oil and monitoring. The $100 you spend doing a shorter interval is good insurance for avoiding issues and keeping fresh, clean oil in the engine. Typically the filter should be changed regularly, even if you are not changing the oil itself. This will insure you will get the maximum life out of both the engine and oil.

What does Motor Oil do?

Most people believe that motor oil is there to lubricate all the parts within the engine, but in reality motor oil does considerably more than that to keep your engine running. Here’s a list of what motor oil does in order of importance.

  1. Separates Metal Components
  2. Cools Engine Parts
  3. Lubricates Rotating Assembly

Separates Metal Components

Oil is pumped through the engine at a high pressure by the oil pump. This oil follows small passages throughout the engine called oil galleys. These paths lead to critical points in the engine like the crankshaft, rod bearings, camshaft(s), and even the turbocharger if your engine has one. Each of these components needs to float on a very thin layer of oil in order to avoid wear and rapid engine failure. This oil boundary layer is forced between the bearings (small sacrificial pieces of soft metal) by the oil pump’s pressure. This is the most important function of the oil. Without this layer, the engine would fail in seconds.

Cools Engine Parts

We now know that oil flows throughout the engine. It also gets flung all over the insides of the engine by the crankshaft spinning at very high speeds. From there it pulls heat from the various objects that it comes in contact with, namely the cylinder walls, pistons, crankshaft, and multiple bearing surfaces. Without this, internal parts would continuously heat up and expand. This expansion would force the important oil layer out, or cook off the oil, which would lead to engine failure.

Lubricates Rotating Assembly

The primary source of lubrication is the fact that the metal parts don’t touch each other. However, the oil itself and the additives in the oil help to reduce internal friction even further. The benefit is a cooler, longer lasting, and more fuel efficient engine.

Why do you Need to Change your Motor Oil?

Oil wears out, or should I say, oil loses it’s abilities to perform at it’s peak due to a number of reasons. Typically these reasons are as follows.

  • Excessive Heat
  • Viscosity Shift
  • Contaminants
  • Exhausted Additives Package
  • Peace of Mind

Excessive Heat

While your oil temperature might hover around the 210 – 225? F mark, internally the oil will reach much higher temperatures. This can cause burn-off, coking (ashing), and other failures of the oil including a loss of oil pressure due to too low of a viscosity in extreme situations. This build-up of burnt oil can clog oil passages and cause further problems.

Synthetic oil is less susceptible to thermal stress as it was designed to handle it.

Viscosity Shift

oilviscositygain.jpg


Modern oils feature a viscosity range depending on the temperature of the oil. This is ideal because during a cold start-up you want the oil to be non-viscous, but at high temperatures you want it to retain some viscosity to promote pressure at bearing surfaces. This is why you see oil weights like, 10w30 or 0w20. The oil achieves this from it’s viscosity-index modifier additive. Over time, however, the immense shear load at the bearings causes this additive to degrade along with loss due to chemical reactions. This causes the oil to shift in it’s viscosity, which affects oil pressure, flow, and other properties negatively.

Synthetic oil does not rely on these additives as much, and will exhibit less shift.

Contaminants

Oil actively cleans the internal components of the engine. Part of the additive package, particularly in diesel oils, is a detergent. Oil seeks to trap contaminants and pull them away from the components and deposit them into the oil filter, or dilute them into the total oil volume. Some examples of these contaminants are fuel, ash, carbon, water, and glycol (coolant).

Oil temps are almost always regulated above 212? F to boil off any water vapor, but excessive idling in a cool environment can quickly attract moisture. Water is particularly bad because it degrades the oil and ionizes any acids which causes corrosion. Fuel will dilute the oil and cause it to lose a significant amount of it’s viscosity index. As an example, a diluted oil might go from a 15w40 to a 10w30.

oilviscosityshear.jpg


Exhausted Additives Package

Oil lives in a very harsh environment and is asked to do a lot. To help the base stock oil companies will add a proprietary package of additives. These can include zinc dialkyl dithiophosphate (ZDDP), molybdenum disulphide, viscosity-index modifiers, seal conditioners, anti-foam, and other additives. Over time, these additives react with either contaminants or the engine parts themselves which reduces the oils ability to perform.

Common Oil Change Interval Myths and Misunderstandings

The 3000 Mile Oil Change

There is no reason to change the oil at 3000 miles for 99% of the motor vehicles on the road.

That being said, the only danger of short-changing the oil at 3000 miles is that you will just be wasting money and time. It will not harm your engine in the least. If it’s what you know and trust, and you want to throw money away for peace of mind, then keep on doing what you’re doing.

Oil change intervals depend on the engine operating conditions (load, temp, etc.) along with oil volume and oil filter capacity. What works for a 2011 Toyota Camry will not work for a 1988 Porsche 911.

The 15000 Mile Oil Change

It’s just not worth the “savings” to run this long on oil, in my honest opinion. Unless you’ve specifically tested the oil and monitored it for the duration of the interval it’s questionable if you’re not actually causing harm. There are some vehicles that are specified to run for long intervals and some oil manufacturers build their oil to handle long intervals. In the first case, the oil filter will also be sized to handle the large amount of contaminants, but in the second case, you’ll be looking to replace the oil filter regularly to properly run the oil for that length.

Unless you are managing a fleet of vehicles or just really eaten up with long change cycles, I’d recommend sticking to a more frequent change cycle.

My Car isn’t Designed for Synthetic! It’s OLD!

This is an old mechanics tale. Synthetic oil will work in any engine that conventional oil will work in. It has better properties than conventional oil, so in fact, your engine will probably thank you for stepping into the modern age, after all … synthetic oils have been around for over 50 years.

Synthetic Oil makes Oil Leaks get WORSE!

This is hard to say one way or another. Synthetic oil does have the same additives to improve the conditions of the engine’s seals, but it does have superior low temperature flow properties. The latter can work against you, but frankly if your engine is hemorrhaging oil you need to replace your seals, not put sub-par oil in your engine. (That’s easier to type than dropping a 250# transmission in your driveway to pull a $11 seal, but such is the luxury of writing, ha!)

When to Change your Motor Oil

The best starting point is in your Owner’s Manual. It will not only outline the oil change interval but the type and quality of oil you need. Engines are designed with a specific weight and type of oil. This is not exactly set in stone, but if you are using the engine for daily commuter duty or light towing it is the best guideline for you to go off of. If the interval is long, you can short-change the oil if you choose, but if you follow the long change interval, then you’d be best to follow the regimen exactly.

If you use your car for racing, drive it hard, or do a lot of towing it’s in your best interest to change the oil more often. This environment accelerates oil degradation, and its also an environment that requires a lot of the oil. Protect your engine, or enjoy replacing rod bearings and turbos.

If you live in an extreme environment, which includes both HOT and COLD, it is wise to change your oil more often, or at least, being very strict on the OEM regimen. Summer temperatures constantly above 100? F or winter temperatures consistently below 20? F during the hours you drive your vehicle will also accelerate oil degradation. It is wise to consider a higher viscosity oil for the hot summer months, and a lower viscosity oil for cold-starts in the winter.Author Note / Example: I live in Texas, which see’s very high summer temps for at least half the year. My car runs about 20 PSI of boost pressure, which is hard on the engine and heats the oil quickly. As a result, I will run a higher viscosity oil than specified for my engine in the summer months. My OEM calls for a 5w30 but I run a 10w40. As a result I see similar oil temps but with higher pressure which is important since I have very high cylinder pressure pushing on the bearings.

The more oil your vehicle holds the less often you need to change it. Larger oil volumes typically have more to do with heat capacitance, but a second benefit is that common contaminants dilute the oil slower. This doesn’t mean you should run out and put another quart in your Honda Accord, too much oil is bad in many ways.

Synthetic oil will run for longer in any engine. That’s not to say that conventional oil is not good, or that synthetic is worth it for your particular needs, but a good quality synthetic will be better suited to handling long change intervals.

Original Article: http://www.vikingspeedshop.com/oil-change-interval-change-oil/
 

Alin

Diehard Car Enthusiast!
:ty: for this. Very informative. :tup:

On that note, I love wasting money and changing my oil every 3,000 miles. :D :lol:
 

Spamby

Meat Product Toy
Since this was posted to our Subaru specific website, I'd like to add a few points.

Subaru released a TSB some years back pertaining to the turbo charged variants, WRX, STi and FXT. This TSB refers to not using the longer OCI (oil change interval) and to use the shorter OCI every 3k miles. The details are that the turbo filter screen could become clogged and ruin the turbocharger if the longer OCI is utilized.

Also to point out, the oil filter in our cars is ridiculously tiny, much smaller than I should think outta be in there. This makes for a very small filter media and thus a smaller filtering surface. Once this filter becomes clogged, the filter goes into bypass and stops filtering. All of the dirt is now sent to your turbo and other parts of the engine. (Probably why the TSB exists for the long OCI and turbo screen)

We have very little oil even when topped off. 4 quarts in a high performance engine, lol. Less oil is less cooling and less trapping or suspending of particles. Why do big rigs have gallons of oil? They work hard and have long OCI and that added oil helps keep oil breakdown at a minimum and cooling to a max.

So my two cents are to never stretch an OCI on our cars. Our oiling and filter system simply aren't designed for longer oil changes.
 

IGOTASTi

System Operator
Staff member
Since this was posted to our Subaru specific website, I'd like to add a few points.

Subaru released a TSB some years back pertaining to the turbo charged variants, WRX, STi and FXT. This TSB refers to not using the longer OCI (oil change interval) and to use the shorter OCI every 3k miles. The details are that the turbo filter screen could become clogged and ruin the turbocharger if the longer OCI is utilized.

Also to point out, the oil filter in our cars is ridiculously tiny, much smaller than I should think outta be in there. This makes for a very small filter media and thus a smaller filtering surface. Once this filter becomes clogged, the filter goes into bypass and stops filtering. All of the dirt is now sent to your turbo and other parts of the engine. (Probably why the TSB exists for the long OCI and turbo screen)

We have very little oil even when topped off. 4 quarts in a high performance engine, lol. Less oil is less cooling and less trapping or suspending of particles. Why do big rigs have gallons of oil? They work hard and have long OCI and that added oil helps keep oil breakdown at a minimum and cooling to a max.
So my two cents are to never stretch an OCI on our cars. Our oiling and filter system simply aren't designed for longer oil changes.
Thanks for adding that [MENTION=1507]Spamby[/MENTION].
 

Alin

Diehard Car Enthusiast!
Has anyone ever experimented with a larger filter? I remember seeing some mazda filters that mate up perfectly to our motors and are about 1.5x larger.

I have no knowledge in that department. Would a larger filter change the characteristics of filtration?

What about a larger oil pan? More oil = longer OCI? [MENTION=1507]Spamby[/MENTION]
 

Spamby

Meat Product Toy
Has anyone ever experimented with a larger filter? I remember seeing some mazda filters that mate up perfectly to our motors and are about 1.5x larger.

I have no knowledge in that department. Would a larger filter change the characteristics of filtration?

What about a larger oil pan? More oil = longer OCI? @Spamby


I have not used a larger filter though I have seen people flirt with it. I am sure there are a few out there that will mate up. I am sure if someone had time and money they could devise an adapter plate to fit bigger filters. Another is to use a remote filter, people have done this.

A larger filter should provide more filtering media. More filtering media equals more filtration. Imagine if your air filter were only as big as the intake tube. That would get dirty fast, huh? This is why not all oil filters are made equal. Some filters utilize less filtering media, regardless of canister size, and others use more filtering media. This is why it's always a great idea to buy a better filter that packs as much filter into the can as possible. If you change your filter on your homes heat/AC unit, you'll have seen the different choices at the store. The cheap ones being about 6 bucks are usually flat and you can almost see through them. The more expensive, generally the more "pleats" and more dense the material is. The use of pleats increases the filters surface area, for the given space, and thus makes the filtering media more able to catch and hold more crud.

Also, the type of filtering media, usually some kind of paper product or cotton/synthetic, plays a big roll, as well. Filters are usually measured or rated by what micron (micrometer) the filter can catch. The lower the number in microns, the smaller the particle it will catch so and so forth. So a filter with a rating of 5 microns will pull smaller particles from whatever liquid/gas it's filtering as opposed to a filter with a 20 micron rating.

To twist things up and really explode your head, A more dense filtering media capable of filtering smaller particles, will generally be more restrictive than a media filtering for larger particles. So, a less dense filter will have better flow characteristics at the expense of filtering and a more dense material will filter better but restrict flow. Foam air filters are an example of a less dense filter as opposed to paper filters.

More oil doesn't necessarily mean longer OCI. You need to couple that with good filtration and good oil.

A larger pan is always a nice idea. The more oil in the pan, the better ability it has to extract heat from the engine and hold heat without fast climbs in temperatures. The more oil, the more time it takes for said oil to become polluted with contaminants.

Seeing as how our cars can consume large amounts of oil when pushed very hard at track days, it makes sense to increase the oil capacity of our engines. More oil in the pan means a bit less of a chance to run dangerously low and starve your precious engine of its life blood.

Im going to use my Porsche as an example here. The car came from the factory with a fairly well designed oiling system AND is stated for long OCI. 10k-20k miles between oil changes. She holds 8 quarts of oil (yes two gallons) and has a filter can about the size of a tall boy beer. I have managed to squeeze almost nine quarts of oil into the engine if I let the oil drain from both sumps for an extended period. The caveat is that what most people don't understand about extremely long OCI's is that your filter will most likely need to be changed at some point during the time frame between oil changes. So say I go 15k on an oil change I should probably replace my filter around 7500 miles to be sure the filtering abilities air top notch. Big rigs do this, as well. They may see OCI's in the quadruple digits but they change the filters more often.

In closing, you need to have three elements for long OCI, good quality SYNTHETIC oil, big filters or change the filters more often, and an oil capacity that of MORE THAN FOUR EFFING QUARTS!

Oh, and another brain twister - A dirty filter filters better than a clean filter, but at the expense of flow. LOL
 

Alin

Diehard Car Enthusiast!
Your gripe on the 4.X quarts has me asking: why didn't Subaru change the capacity of the oil pan since 2004? Are the cars, as they come from factory, good for majority of the customers?
 

Spamby

Meat Product Toy
Your gripe on the 4.X quarts has me asking: why didn't Subaru change the capacity of the oil pan since 2004? Are the cars, as they come from factory, good for majority of the customers?

It works. That's probably why. Still doesn't mean I agree with it. Design constraints with the manifolds and such being under there so close.

Subaru being a conservative and budget car company? Utilizing parts from other models to keep costs down. Not having the funds to retool and revamp every few years. Look how long they've taken to get a new designed motor? Look how long the 2.5 has been in service. Why do they keep putting shitty Pistons in their performance engines? Why is the tuning subpar?

In the realm of long OCI, this car is not made for that and probably never will be. Get yourself a bigger Moroso or Killer B pan and get an extra quart.
Does it work for most? Yes, it does. It has to and we make it work.

But since Subaru has big brother Toyota giving them cash and advise, maybe they'll start to come around?
 

Robert Viehweger

Daily Driver
Having been modified incrementally over 76k miles on my 2011 STi, lots of people say I waste a lot of oil changing every 3500-3750. I've also seen many people with blown motors with much less miles. Are the two correlated? I have no idea. Do I have a fully functioning motor in the 350-400 whp range on stock block? Yes. Is that peace of mind worth an extra $50 in oil a year vs. a new $3000 motor? Most definitely. To each their own, I'm not paying for anyone else's stuff but mine, but if you can't afford an extra $50 a year for clean oil, you probably shouldn't be driving an STi.... just sayin...

Also, I get the mobile 1 extended filter and change that every other oil change. It's worked well for me, but I'm not tracking this thing, either. :p
 
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blee2666

New member
Good Info. Thanks for the write up. IMP, If you think you might need to change it for what ever reason, (hard driving, cold, hot, city, etc.) change it. 60 bucks for a lof is great for your peace of mind.
 

Grinder34

Track Monkey
Also,

What would lead to a longer OCI recommendation from the factory?

Example:

E39 M5 is definitely a "sports car". I believe the factory recommended change is roughly 15k miles. There is an indicator that integrates things like RPM, driving style, etc... and can indicate a change is necessary sooner, but even on the M5 boards people are waiting 7.5-10k miles.
 

Alin

Diehard Car Enthusiast!
Also,

What would lead to a longer OCI recommendation from the factory?

Example:

E39 M5 is definitely a "sports car". I believe the factory recommended change is roughly 15k miles. There is an indicator that integrates things like RPM, driving style, etc... and can indicate a change is necessary sooner, but even on the M5 boards people are waiting 7.5-10k miles.

Dang, that is mind boggling. I've changed the oil on every single vehicle I've driven every 3k miles. (performance or not) Sometimes, I allowed it to go to 4k, but no more. I understand the longer periods IF you're ALWAYS driving like a grandma and babying the car. Let's be real here, anyone who has a performance vehicle is going to drive hard every now and then, unless they're ALWAYS driving hard.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
Also,

What would lead to a longer OCI recommendation from the factory?

Example:

E39 M5 is definitely a "sports car". I believe the factory recommended change is roughly 15k miles. There is an indicator that integrates things like RPM, driving style, etc... and can indicate a change is necessary sooner, but even on the M5 boards people are waiting 7.5-10k miles.

To each their own, but this is why I roll my eyes when people berate me for changing oil at ~4500 miles. :lol:

If I'm tracking the car a lot, especially in high summer temps, the oil gets changed no later than 3000.
 

truckerhucker

New member
i change my oil every 2500 miles the guy who i bought my sti off said oil changes every 4000km no exceptions. for a long engine life is he pulling my leg
 

Alin

Diehard Car Enthusiast!
i change my oil every 2500 miles the guy who i bought my sti off said oil changes every 4000km no exceptions. for a long engine life is he pulling my leg

It really comes down to how you drive the car, honestly. If you drive like a grandma, you shouldn't have any problems pushing 7,500 miles on an oil change. If you drive like you stole the car, it would be wise to change it every 3,000 miles. The only way to get a true answer is by doing an oil analysis test. Blackstone Labs is the company who I've used multiple times in the past.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
i change my oil every 2500 miles the guy who i bought my sti off said oil changes every 4000km no exceptions. for a long engine life is he pulling my leg

Like Alin said, driving style has a big effect on when your oil NEEDS changed.

But one thing you should make a habit of, is checking your oil level regularly. ESPECIALLY if you are exceeding normal oil change intervals. These cars CAN eat a lot of oil between changes and if you aren't paying attention, you could create a very expensive headache for yourself.
 
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