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Synthetic Oil Change Interval. All you need to know to Stop Wasting Money.

The correct synthetic oil change interval is an extremely important thing when it comes to keep your car’s engine running nice and smooth for a long time.

But we all know that synthetic oil does cost some good money so we don’t want to change it prematurely, right?

We also don’t want to extend its service life too long and end up damaging the engine.

Let's dive right into this!

Synthetic Oil Change Interval

How often should you get an oil change?

For those who have no more than 1 minute to get an answer to this issue here is your short answer:

  • Synthetic oils have an average 7000 miles life in them.
  • Full synthetic oils have around 10000 miles worth of proper lubrication in them.

But what is that about "synthetic" and "full synthetic"? Well, for that you'll have to stick with us a little more because this is really worth diggin' into.

Grab a drink. Let’s do some realtalk.

Among all members (editors, friends, family and contributors) of Gear4wheels we’ve owned many, many cars (and quite a few motorcycles, one snowmobile, two atv’s, four 49cc scooters and other unconfesable things with wheels) and we’ve always followed the “3000 miles or 3 months” oil change rule. And you’ve probably had too.

Now things have changed a little bit in the oil scene and synthetic oils are becoming the norm. Manufacturers now recommend longer oil change periods as long as 15000 miles (In Europe, some manufacturers that recommend Castrol Longlife go up to 20.000 miles) and there is a lot of discussion on the topic.

We are going cover one by one the factors that will determinate how long is your oil going to live before you have to put it back on a can and bid farewell, and to reveal why we do not follow that rule anymore. 

The 3000 miles rule.

This apply to conventional mineral oils.

They are overall low-performance oils even when new. Check the following image (Courtesy of Pennzoil) in which they are comparing Synthetic Vs Conventional oil.

synthetic oil change interval affects oil flow

They let both oils run at the same time. Synthetic runs quickly and smoothly and conventional takes longer to touch metal. It looks thicker. And those are both brand new oils…

This image shows used vs new oils both (courtesy of Engineering Explained)

oil flow comparison

You can very quickly see that whilst all three other oils ( new and used synthetic, and new conventional oil) have already touched the metal and are flowing, used conventional oil is barely dripping from the test probe.

The image is quite self-explainatory. Conventional oil loses properties with time and use and has to be replaced frequently to ensure that engines running it are actually well lubricated. 3000 miles has always been the rule. Good.

So what happens with synthetic oil then?

Here is the tricky part. There are semi-synthetic oils and full synthetic oils. They have different lifespans as how many miles can you run them before they turn into solid grease.

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Synthetic and Full Synthetic.

Whether an oil is labeled as synthetic or full synthetic depends on one key factor: The used base oil. The American Petroleum Institute (API) has divided them into 5:

synthetic oil base stocks
  • Group I, II and III are refined from petroleum crude oil.
  • Group IV are polyalphaolefins and Group V are Esters. Only oils that use this two groups as a base are full synthetic oils.

Synthetic oil change interval: What manufacturers say.

Remember that short answer we've given at the beggining of this post?

​Synthetic oils have an average 7000 miles life in them.

​Full synthetic oils have around 10000 miles worth of proper lubrication in them.

Gear4Wheels 
About what Oil Makers say

That’s what most oil brands tell about their oils. Some car manufacturers elongate this a little more (Jaguar recommends 15.000 miles for full synthetic) but they also say “Under ideal conditions” which 99% of the time aren’t the real conditions.

FACTORS THAT AGE OIL QUICKER.

So as we have mentioned, those 3 numbers, 3.000, 7.000 and 10.000 miles are not set in stone. Take them as a guideline.

There are many factors that will have an impact on the oil and likely make it lose properties quicker. Lets see a few:

  • Diesel Engines: Diesel is a less refined product than gasoline. It produces more soot and acid by-products.
  • High-Mileage Engines: Engines with a lot of miles on their back generate more blow-by gases and unburnt fuel that gets into the crankcase.
  • Turbocharged Engines: Turbos can spin at over 100.000 rpm. Once you shut off the engine, it still spins for a while (although you should leave your engine to rest a few seconds after you stop before you shut if off to let the turbo reduce its spin back to idle) the high heat built in bearing surfaces may cause oil to crack forming hard carbon deposits and hydrogen.
  • Short trips: Specially in winter. The engine doesn’t have time to reach the optimal working temperature. Low operating temperatures cause moisture and byproducts of combustion to build up in the oil. This will generate waste deposits and acid in the engine that can lead to faster wear on pistons,cylinders, bearings and crank journals.
  • Your driving style: The more aggressive you drive (high revs, quick accelerations etc) the more you are asking out of your oil.
  • Road dust: Driving in very dusty environments will make your car suck a lot of dirt. A good air filter will retain everything that is bigger than a micron, but everything else will pass through and go into the oil. A good quality oil filter will retain all those particles but this will indeed shorten the life of the oil.
  • Towing/Heavy loads: Increased duty, higher temperatures that increase metal wear. Wear metals cause premature oxidation, sludge, acids and deposits.
  • Bad Oil Filters: The oil filter is a key component of the lubrication system. They accumulate all the nasty stuff such as dirt, water, metal particles etc that gets into the oil (the very same particles we've just seen that age oil quicker) Bad oil filters barely filtrate such harmful agents, so make sure you are using the best oil filter on your car.

So will a diesel pickup with 130.000 miles that’s usually used to bring construction materials to Uncle Ben’s farm in Omaha be good with 8.000 miles between oil changes? Hell no.

Let’s be clear. There is no magic calculator in which you input every variable and it gives you an accurate number of miles inbetween oil changes.

Our recommendation for you is to get the best synthetic motor oil, the best oil filter, and then take into consideration all those factors and think “Ok so if this oil is supposed to last 10.000 miles, I do a lot of short trips, my car is gasoline and it hasn’t got a turbo and I do REALLY care about it lasting a long time… let’s do 6.000 miles from change to change” for instance.

We encourage not to drive over the “recommended” miles. And since there is a lot of discussion lately on why manufacturers are constantly changing their recommendations, we also want to share our take on this trend.

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From 3000 miles to 20000 and back to 10000. What’s changed and why.

So the first thing is clear. Synthetic oils last longer and overall perform better. But 15000 or even 20000 miles is pushing it way too much. BMW recommended 15000 miles or 24 months around 2013… but then for all 2014 models and applying to older cars too, they changed to 10000 miles or 12 months. Why that change of mind?

A high rate of failure of mechanical parts at low mileage, essentially.

Car manufacturers are responsible for as long as the car is on warranty. Short-term problems are their problems. But long-term problems are their profit.

So basically once they saw that their oil change schedule was costing them a lot of money, they decided to shorten it.

Same with break-in oil changes. It is costly for manufacturers to do it after 1000 miles. They will refuse to conduct it, literally. But that is the moment in which you should do it.

About Computer Oil Life Monitors

You might think “Hey my car comes with Oil Life monitor built-in, I know when to change my oil”and it is a fair thought.
You’ve paid for that feature don’t you? But here is the trick to that.

Most systems (GM, Ford, PSA to name a few) calculate the oil life based on data collected from different engine sensors. The engine computer will calculate based on an algorithm and all that data and provide a “result”.

It is pure software. Ever tried to lose weight and followed something that looked great on the book but the results weren’t as expected? Pretty much the same.

There is no sensor actually in your oil pan. So with no actual readings being taken straight from the oil, you cannot know precisely what is going on. Just an “estimate”.

Some BMW and Mercedes Benz do have a sensor in the oil pan, but as every other sensor, they can malfunction and get contaminated by a lot of agents, providing wrong lectures.

As a quick footnote, a sensor that’s malfunctioning won’t light the “Check Engine” pilot unless the data it provides is off-range.

If the measure is “reasonable” for the on board computer, it won’t turn the dreaded light on. Even if it is wrong. So, yeah, they give you some information but don’t take it as a final word.

By the way if you're serious about your car and want to discard such problems as sensors working "fine" but actually measuring cows instead of ducks, get an obd2 scanner, one of the smartest investments you can do.

Environmental Issues

One liter of oil contaminates one million liters of water. Let that sink.

Service stations will collect used oil, whether they have changed it or not. In the end, they sell it at a quite good price so it’s worth the effort. Unnecessarily frequent oil changes will have a negative impact on the environment and we should bear that in mind.

However, disposing the highly contaminant waste on the right place should be our #1 concern.

DISCOVER THE BEST SYNTHETIC OILS

I've conducted some MASSIVE research to craft a list of the top synthetic motor oils in the market. 

Final Thoughts.

The right synthetic oil change interval will keep your engine properly lubricated, ensuring the right performance.

It will save you a lot of money in expensive repairs.

Just be sure to change your oil filter at the same time, follow our recommendations for a successful change if you do it yourself and ensure that you dispose the used oil at the right place.

Alex Meyer
 

Alex Meyer is a 26-year-old Certified Automotive Technician with over 10 years experience as a mechanic and car audio installer. He shares his knowledge at Gear4wheels.com

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