Quote:
Originally Posted by RT-NY
Are you saying that changing the oil regularly in a vehicle that isn't driven much is not necessary? Is there any time-limit or is the oil good indefinitely?
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I will let Avanti speak for himself to your query, but will add some clarity as I see it to the issue.
I have torn down quite a few used engines over the the past decades so what I found is based on what the insides looked like for wear and tear or other issues.
I would totally agree with Avanti on the oil itself being just fine and it will last a long time, even years, in an engine. I have not seen a sludged up engine, on the oiled parts anyway, in many years and most are quite clean if good oil is used.
What I have found for years, and it has not really changed much on the Minnesota engines I have torn down is what I would water/acid issues, particularly in the main, rod, and cam bearing, which are babbit, trimetal, or aluminum for the most part these days. Trimetal in many high peforance or high rpm engines, aluminum now very dominant in daily driving vehicles because it lasts and on time and is cheap.
What I find in low mile engines is that they probably aren't driven enough to evaporate out all the water, and the generally low per year miles entails short trips, which commonly put more acid contamination into the oil because of more cold starts per mile and lack of long highway drives at full temperature.
What I see is erosion particularly in the lower (cap side of the main bearings and cam bearings, and on the rod bearings more generally around the in the lower side which is different side to side on V engines and compared to verticals or boxers.
Mostly not enough for major concern but does make for shorter engine life by some amount due to dropping oil pressure or possible bearing tear out of the surface if it gets too bad, IMO.
Sometimes there is also rust in the low spots of cast iron areas and sometimes in rockers and hydraulic lifters if they use them.
In general we are talking life changes that only show up later in the lifespan of the engine, Maybe the difference between needing a rebuild at 150K instead of 200K and most low yearly vehicles are dead from other reasons because of age by then, with the exception of collector stuff and exotics.
If there is any issue a person is worried about because of low miles per year, just send in some oil samples for analysis to see what it looks like and pay attention to acid and water content and related additive depletion because of it. Keep stretching it out on changes until the analysis starts to say it getting a bit long and back off a bit. I have done this several times, particularly with summer driven hotrod type vehicles and if they vehicle is stored in a climate controlled where it won't breath in moisture with temp changes and driven longer distances when driven, I could see going several years without changing oil without issue.
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