I have a question about conventional vs. synthetic oil at the other end of the spectrum

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kingfish

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I own a vehicle which I put less than 1000 miles per year on. It currently has about 5500 miles on it. I did an oil change at 3500 and put synthetic in it. My question is about the stability of conv. vs syn. in this situation. Many oil mfg. have started saying you should think "months not just miles" in their advertising. I have heard anecdotal reports that conv. oil will loose its anti corrosion properties over time. I don't recall anyone stating that syn. does the same, but it may very well do so as well. So the issue is should I use conv. oil and change it every year or use syn. and leave it for a few years? Third option would be conv. and leave it in until I put another 3500 miles on it which should still be well within the lifespan conv. unless the anti corrosion properties factors into it. What say ye all.
 

GC7

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No way to know exactly without doing a used oil analysis to understand what the oil's TBN (total base number) is after high time/low miles.

But generally speaking, even if you put on low miles, as long as you are driving it long enough to burn off crankcase condensation with each drive then you are helping to prolong the service time between oil changes. Crankcase condensation increases acidifcation of the oil which depletes its protective properties.
 

kingfish

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No way to know exactly without doing a used oil analysis to understand what the oil's TBN (total base number) is after high time/low miles.

But generally speaking, even if you put on low miles, as long as you are driving it long enough to burn off crankcase condensation with each drive then you are helping to prolong the service time between oil changes. Crankcase condensation increases acidifcation of the oil which depletes its protective properties.
When I do drive it, it is usually for over an hour so the cook off should be good.
 

GC7

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When I do drive it, it is usually for over an hour so the cook off should be good.

In that case you are fine either way. The additive package that goes into conv or synth is largely the same (zinc, phos, moly, calcium, boron, etc), but synthetics are often specified in case of "thinner is better" (good luck finding a conventional 0w16 oil like Toyota and Honda have started to spec) or severe duty (new Vette high performance engine, newer Turbo engines).

*Edit - One thing I forgot to mention - if your engine has a tendency towards fuel dilution, that can also reduce the service life of the oil. A UOA is the only way to know the actual percentage, but if the oil starts literally smelling like gasoline after a few hundred miles then factor that in as well. Newer direct injection engines seem to have this problem more than older port injection engines, but it just varies based on the design.
 

Shadowrider

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You should change your oil once a year no matter what. The corrosion additives will break down. It's a chemical thing with the combustion byproducts it's in contact with. Once you pour it in and start it up the clock starts ticking.
 

OlBrownTruck

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I agree with Shadow rider. I would change it at least every year regardless of the miles. If it sits for extended periods, everything above the oil level will 'sweat' over night when the temperature drops. That condensation will run down and pool in the bottom of the oil pan because water is heavier than oil. Then, when you start the engine, the first thing it gets is that water.

It may not be much unless it sits for a very long time. It's worse in the spring and fall, when it cools off more over night. If you go out in the morning and there is a heavy dew, just know that the same thing is happening inside your engine. As I said earlier, everything above the oil level will sweat inside the engine.
 

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