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it's not a good sign if it goes black though... right?
I think the darkening is also due, probably as minor contribution, by tiny metal particles from the engine.
Quote from: lightarrow on 24/07/2007 19:54:06I think the darkening is also due, probably as minor contribution, by tiny metal particles from the engine.Thank You Alberto...........so is that as a result of general engine wear and tear ?........
The crankcase (where the engine oil circulates) lies directly beneath the travel of the pistons in the cylinder. When the fuel burns in the cylinder above the piston it produces gas under pressure. The expansion of this gas drives down the piston generating useful work.The pistons create a seal against the side of the cylinder using piston rings which encircle the piston and form a close contact with the cylinder wall. But the seal isn't perfect and some of the gas created by combustion leaks past into the crankcase. There are carbon particles in this gas, which deposit onto surfaces inside the engine. When the oil washes over these surfaces as it lubricates the engine it picks up and suspends the particles.The slowly aggregate into larger clumps which are sieved out by the oil filter, but some are tiny and remain suspended in the oil, slowly turning it black.This is in addition to the contribution of metal particles and other oxidation products formed by heating of the oil itself.Just as an aside, the gases entering the crankcase in this way are allowed to escape via an "oil breather". On some engines (such as old diesels on tractors) they come out through valves on the side of the engine block. More normally, however, they pass along a tube which blows them back into the air intake, so they re-enter the engine and are burnt.This is cleaner and more economical because the air entering the engine is warmer, which improves fuel vapourisation and cold-running, and the incompletely-burned hydrocarbons can also be burned, yielding energy whcih would otherwise be pollution.My lawn mower uses this system. The downside is that when you tip it up to clean the blade and underside, if you tip it the wrong way all the engine oil ends up in the air filter. Then when you next run it the engine does a very good impression of a smoke machine...Chris
Wifeys toast and car oil have this one thing in common !...they go black !I know why wifeys toast goes black but why does car oil go black ?....where does the black stuff come from ?...what is the black stuff ?I don't think it's wifey scraping her toast where my dip stick goes !...so what is it ?
Quote from: neilep on 23/07/2007 22:13:19Wifeys toast and car oil have this one thing in common !...they go black !I know why wifeys toast goes black but why does car oil go black ?....where does the black stuff come from ?...what is the black stuff ?I don't think it's wifey scraping her toast where my dip stick goes !...so what is it ?Neil You need to change the oil when it gets black and sludgy.. also take time to get a new Oil filter! They are easy to replace depending on where yours are located. I have seen some of the newer cars that you just about have to drop the engine to change the filter.. a stupid design for sure!