Why is it necessary to change vehicle oil regularly, and not just change the filter and add new oil as needed?
In: Engineering
There does appear to be a US obsession with changing oil.
Almost all oils are synthetic oils now and behave very differently to traditional mineral oils. They last longer.
Engines are machined to fit together much better than they did in the old days.
So you don’t need to change your oil every 5000 or 6000 miles. Most cars tell you when to change the oil.
What I would like to see is a properly controlled study between regular oil changes and changing oil when the car monitoring tells you to. Only this way will we really know if we should change our oil more often.
But with more electric cars on the road this becomes a moot point.
Only engine oil needs frequent change. Mostly because of fuel contamination, moisture (water) and extreme pressure and extreme heat. Oil in sealed gearbox can be left there for almost a lifetime without major failure. Though not recommended.
In an engine sludge will make it fail eventually if not changed regularly. The filter is only there for physical contaminents.
Think of your oil as an animal product, like meat or fat. When you start heating up a slice of delicious bacon, at first it still looks mostly the same and stays soft. After a while it gets crispy and turns the right color. And if left too long, it’ll burn and turn black.
That red crispy bacon is ideal for what you want to do with it. That black burnt bacon is not useful.
Well, inside your car’s engine the heat stays on whenever it’s running. Your oil, just like that bacon, will eventually turn black and be unsuitable for your purposes.
So then we put some fresh slices of bacon in there and heat it up. When they get black and burned, or hopefully before it gets to that point, we swap to fresh slices again. And again. …
The oil itself degrades with use in an internal combustion engine. Its not possible to completely seal the oil from combustion.
The viscosity (gooeyness/thickness) of the oil breaks down over time, so even if you had an improved/oversized filter that could keep the oil really clean and you replaced it every few hundred miles, the oil itself would gradually become less effective at protecting the engine.
Oil is an extremely good lubricant however over time the parts will still slowly wear down and these very very fine metal shavings slowly accumulate in the oil and can eventually act as an abrasive. This is why it’s necessary to change both the oil and filter instead of just topping it off. Sometimes so much wear metal can accumulate in the oil that it actually turns silver and at that point the engine is done. Also over time oil becomes less stable and more volatile due to repeated heating. This can come as evaporative loss where you actually lose some oil.
Because we use low quality oil filters and don’t really filter all the oil just the stuff going to the pump. It’s easy and pretty cheap to just dump the oil and put fresh in.
On larger equipment you can. Have bypass filters. This allows more oil to be pumped through a second filter cleaning it. Just changing the filters you can run many miles.
https://www.thebestoil.com/products/bypass-oil-filtration/?gad_source=1&gclid=Cj0KCQjw6PGxBhCVARIsAIumnWaS29KelCpfy7FX0ObdTH_i6SPs1uPU5-5qTp9OGlqka9SEFYuNwmUaAlM5EALw_wcB#1501001964602-5e421a97-6961
I believe amsoil has ran a semi a million miles on the same oil just changing filters , but I can’t remember the exact mileage.
Oils have additives in addition to a base oil. As the oil is used, the oil itself stays healthy, but the additive package begins to delete itself and starts to fail to provide benefits like engine cleaning and particle suspension (which carries dirt to the oil filter). In addition, gasoline or diesel gets past the rings as the vehicle is run, diluting and thinning the oil reducing its lubricity and ability to withstand the required pressures required for bearings and cams.
New oil replenishes the additive package, and replaced the fuel-thinned oil.
The filter keeps stuff out of the oil but the oil it self goes bad and stops being able lubricate the engine properly after enough time and or usage has passed. It gets heated up and cooled down and churned up by the engine over and over and eventually goes through chemical changes that make it less effective. This causes increased fritcion and thus wear and tear on the engine which if left to get bad enough will greatly shorten the lifespan of said engine.
The oil filter is not perfect either so contaminents will still build up. Just being outside like most cars are is enough to age the oil over time.
I mean, I’ve had an engine that burned and leaked oil BAD. Like basically replacing all of the oil every 2 months or so. On that vehicle I just changed the filter every 4 or 5 months because the engine was changing its oil on its own.
But for properly running engines they really don’t burn much oil so adding new oil as needed doesn’t really work, at least not enough to have good fresh oil when its needed.
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