Milage vs time for changing oil
September 12, 2016 7:25 PM   Subscribe

Milage vs time for changing [synthetic] oil

I only drive about 1,200 miles a year (not much highway driving). I change the oil every couple of years or so. When I had it changed a few weeks ago, the local garage took it upon themselves to use synthetic oil. Two questions:
1 – Should I still change it every couple of years (how quickly does synthetic oil degrade over time?)
2 – Can I go back to regular oil (not necessarily going to, but if doing so is detrimental, I want know that).
93 VW Corrado; 65,000 miles (original owner)
posted by pmaxwell to Travel & Transportation (12 answers total) 1 user marked this as a favorite
 
2. Yes.
1. You should change it every year. Moisture is the enemy, not oil degradation.

I loved the Corrado.
posted by LoveHam at 7:55 PM on September 12, 2016


I'm not sure where you are, but if I were in an aggressive climate, I'd change the oil at least every year - just after winter for a mild climate, maybe twice a year for a more severe climate. As mentioned, it is more about temperature changes, moisture and corrosion encouraging stuff in used oil that is the issue.

There is no reason at all why you can't go to regular oil after this change. Personally, in your shoes I'd have cheaper oil and change it more often, than more expensive oil and change it less frequently. I mean, don't use $2 per gallon recycled mcdonalds fry oil, but a reasonable, mid range non-synthetic and change it more often.
posted by Brockles at 10:18 PM on September 12, 2016 [1 favorite]


With such low mileage moisture and acid are the problem rather than any sort of particulate loading. You pickup moisture from the air just sitting. IE: oil in a sealed bottle will last pretty much forever but churn it in an engine regularly and it'll degrade. Short trip, low mileage usage is perty tough on oils.

What is your pattern like? 6 miles a day broken into two trips where the engine cools at the half way point (IE: driving back and forth to a close workplace)? Or 50 miles every second weekend taking a drive out somewhere. The more the former the more often you should change your oil. If it is the former I'd change it twice a year (and I'd take your car on a 30 minute trip every once and a while to get things like diff fluid and power steering fluid warmed up. If it's the latter I'd probably push it to once a year in the spring.

You can freely mix synthetic and regular oil. I'd probably stick with synthetic for piece of mind considering the annual cost is so low but it is likely to be a minor waste of money. Regular oil would be fine unless your owners manual recommends synthetic.

PS: you should be thinking about changing your other fluids too because they won't be hitting any sort of wear replacement with such low mileage. Brake fluid (because it hydroscopic) and coolant (because the corrosion inhibitors can get wore out) every few years and transmission/transaxle/differential fluid every 5-10 years.

Also tires have a lifetime of 6 to 10 years depending on whose guideline you want to follow.
posted by Mitheral at 11:27 PM on September 12, 2016 [1 favorite]


I put about 5000 miles per year on my car and change the oil twice a year, for the moisture accumulation reasons mentioned above.
posted by mskyle at 4:47 AM on September 13, 2016


I would say save your money and never change your oil. The moisture thing is really overrated. In just a few miles of driving your engine oil should get hot enough to drive off the small amount of moisture dissolved in the oil. Within three miles of driving your oil temperature should be up to around 230 degrees.

But who cares, anyway? At the rate you are driving you will only have 12,000 miles over the next decade. Your engine will be fine. Even if engine wear is doubled or tripled, it is only the equivalent of 24K to 36K miles. By that time your car will be 33 years old. Do you plan on driving a 33-year-old car?

So forget about it. Let us know in 10 years how it goes. It will be a great experiment.
posted by JackFlash at 10:42 AM on September 13, 2016


The moisture thing is really overrated. In just a few miles of driving your engine oil should get hot enough to drive off the small amount of moisture dissolved in the oil. Within three miles of driving your oil temperature should be up to around 230 degrees.

To clarify this misinformation, JackFlash is tangentially addressing a different aspect - when you drive lots of short distances, you do need to make sure you get your car fully warmed for several minutes (a 20 minute drive is plenty) to make sure that the oil is hot enough to evaporate all the water out of the oil and the various nooks and crannies of the engine. A fully warm engine will pretty much rid itself of the moisture from sitting around from extended periods within a 15-20 minute drive. It will, though, take significantly longer than three miles to get the oil up to 230 degrees F.

However, that isn't the issue. The moisture collects within the engine after being run and during normal day/night temperature cycles in the form of condensation (it is not a sealed unit). The time that the car sits without being run to burn off this moisture is the issue - especially when added to the impurities and corrosive elements produced by degraded engine oil. So, yes, the moisture is an issue, especially and particularly in an occasionally used car. During this period oil film runs off the moving parts in your engine (over time) and leaves exposed metal that is prone to corrosion, which creates accelerated wear in the engine when it is used again (as the corrosion needs to be 'worn off' next time it runs).

Try not to let your car sit for extended periods without being run. No more than a month, I'd suggest. Less if you live in a high humidity or aggressive climate. It's worth starting and running the car (ideally driving it) within that period to make sure everything stays as close to optimum as possible.

The advice to never change your oil is irresponsible and based on faulty reasoning.
posted by Brockles at 11:37 AM on September 13, 2016


The advice to never change your oil is irresponsible and based on faulty reasoning.

Actually the reasoning is quite sound. It's a 23-year-old car. They only drive 1200 miles a year. How much longer is the OP going to continue driving that old of a car? Even if oil consumption increases over the next five years due to purely hypothetical increased wear, so what? They may have to add maybe two quarts a year instead of one quart a year. That's a lot cheaper than 8 quarts of oil changes a year. Why bother?

And the nonsense about condensation from the engine, what, "breathing", while sitting is just that, nonsense. Any hypothetical moisture is going to get into your engine whether you change oil once a year, twice a year or never. The difference will be almost immeasurable. The (very small) air space in your engine has the same amount of moisture in it whether you changed your oil yesterday or a year ago. And tomorrow it will again have the same amount of moisture in the air. Changing oil doesn't change the amount of moisture in the air.

You simply cannot quantify any serious problems that would develop over the next 6000 to 12,000 miles no matter what you do with the oil. Better to save your money for all the other actual showstoppers on a 23-year-old car that are likely to crop up rather than worrying about the possibility of slightly increased oil consumption years in the future when it will be a 28-year-old car.
posted by JackFlash at 12:41 PM on September 13, 2016


Jackflash is WRONG, sounds like my sister in law that thinks because she doesn't drive the interstate she doesn't need to change her oil.............shes blown 3 motors over the years & doesn't understand why........change it once a year. all the other advise was good too. Hey Jack, how many cars you owned?
posted by patnok at 1:06 PM on September 13, 2016


shes blown 3 motors over the years & doesn't understand why

Why? The likely reason is she ran out of oil, not because she didn't change her oil.

Not changing the oil and driving 1200 miles a year is not going to "blow up an engine" as long as the oil level is checked regularly.
posted by JackFlash at 1:26 PM on September 13, 2016


Jackflash, your answers show a serious lack of consideration of all the issues involved. Based on experience with you in automotive questions here, there is no point arguing with you, because you never budge from your position, regardless of how much your statements are refuted. However, I will highlight the biggest issues in your answer for the benefit of others who wish to learn:

Even if oil consumption increases over the next five years due to purely hypothetical increased wear, so what? T
It is telling that you think the only issue from not changing oil would be to increase oil consumption, then no wonder you think it doesn't matter. Increased oil consumption is the least of your worries from poor maintenance and over-due oil changes.

Usual causes of increased oil consumption: Piston ring wear, valve stem oil seals wear, head gasket or external gasket leak. Only the first two are likely as a result of a vehicle sat for a long time or poor oil quality.

Just a few of the possible problems from poor oil film coverage, internal corrosion or otherwise caused by not changing the oil, all of which are exacerbated by engines sitting idle for extended periods because of the corrosive effects of used oil, coupled with moisture on bare metal surfaces over time:
Bearing corrosion or damage - accelerated wear of bearing which can lead to direct component failure, plus also sometimes loss of oil pressure, which can also cause considerable accelerated wear in other components and additional component failure. This can things such be cam bearings, tappet or valve lifters, crank main bearings, Piston connecting rod bearings (little and big end). Often with bearing damage, comes 'knock on' effect damage as the bearing fails and small particles of the failed bearing travel through the oil system and can block smaller oil passages, or just get caught between other bearing surfaces and cause and increase wear.
Piston Ring corrosion - causes increased oil consumption, and/or increased blow-by, resulting in poor engine performance, loss of fuel efficiency.

The (very small) air space in your engine has the same amount of moisture in it whether you changed your oil yesterday or a year ago.

This is patent nonsense. You are clearly far out of your depth. Oil itself is Hygroscopic, which immediately makes your statement false. Educate yourself here perhaps.

In addition, the air space in an engine is at least equal to the volume of oil in the car. Usually it is bigger (if you count the cylinder volume, which you must if the car is stationary for extended periods as the seals are designed to work most efficiently when in motion and with an oil film, which can disappear over time).

You simply cannot quantify any serious problems that would develop over the next 6000 to 12,000 miles no matter what you do with the oil.

This is true, but an oil change is preventative maintenance. Engines need preventative maintenance to maximise their efficiency and extend their life. Using the argument that the life of the car is likely small enough that 'fuck it, just ignore maintenance because why the hell not' is asinine and devoid of supporting facts. People come here for facts, not your outdated and unsupported opinion. The premise is how to look after the car, not 'shall I just let it die'.
posted by Brockles at 2:04 PM on September 13, 2016


Well, we will just have to agree to disagree. You have provided zero evidence to quantify your beliefs. The OP is driving an average of 25 miles per week. They aren't going to saturate their engine oil with water. And even if they did, can you quantify the difference between changing the oil at 6 months vs never. The oil is still going to have the same amount of moisture in it most of the time or not enough to make any quantifiable difference in the engine.

Save your money, don't bother changing your oil. Nothing bad is going to happen in the next few years.
posted by JackFlash at 2:39 PM on September 13, 2016


The annual 1,200 miles are driven over four months (June thru September). From Oct thru May the car sits unused in a shelter (Northeast winter conditions). And, yes, JFlash, I hope and plan to be driving it when its 33 years old and beyond!
posted by pmaxwell at 8:58 PM on September 13, 2016


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