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Originally Posted by Artan
Mr. Dremd; I regularly check the oil in my car. I put some on my finger and supressit it with other finger. ON the other hand i put the same oil but NEW to check if there is a difference between old and new oil. Absolutely nothing. The viscosity is totally the same.
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This is ridiculous, really.
The low temperature viscosity isn't the real issue either, it's the high-temp viscosity you need to know and measure.
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If metal particles would be big you would feel it on your finger.
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Many vehicles have magnetic oil drain bolts.
They collect a fair bit of metal parts that you can really feel.
Even small metal parts in oil are abrasive when they get in between the surfaces they need to lube. All this junk accumulates over time.
Metals are also an indication of the wear of the engine.
In a diesel, soot also accumulates in the oil.
That's not good either.
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I am absolutelly convinced that we never need to change oil in the engine as long as the oil doesnt get contaminated with water, fuel, other external chemicals or contaminants.
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Never may be a very bold claim, but oil is often changed far too frequently.
A friend of mine went 90.000km / 56.000 miles on the original (and very expensive) oil in his diesel Beemer.
Many trucking companies run long oil change intervals, with multiple filters, including a low flow, very fine bypass filter to get the smallest particles out.
A car usually has but 1 filter.
Direct contamination with fuel or water will certainly ruin the oil quickly.
Oil dilution has become an issue with more modern diesels with particle filters, or when you're running biodiesel.
The oil in the engine isn't sealed off from the atmosphere, so some water vapour does get in and out with temperature changes.
Remaining TBN is the factor to look for when you want to run your oil for extended periods. It will go down over time, and ultimately will indicate when it's time to get rid of the oil - if it hasn't accumulated so much crud that it needs replacing before the TBN drops too low.