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Author Topic: Why Does Car Engine Oil Go Black ?  (Read 24032 times)

Offline neilep

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Why Does Car Engine Oil Go Black ?
« on: 23/07/2007 22:13:19 »
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 ?
« Last Edit: 14/04/2015 08:30:43 by chris »


 

Offline daveshorts

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Why Does Car Oil Go Black ?
« Reply #1 on: 23/07/2007 22:46:05 »
I think it is mostly the same stuff - carbon, coming from a very similar source - Incomplete combustion. So your wife's toast goes black when the hydrogen and oxygen are burnt off the starch leaving carbon, and if your engine does not quite burn all of it's fuel (or partially burns some of the oil lubricating the cylinders) it will also make carbon.

Also finely ground up metal will look pretty dark, but hopefully there isn't too much of that in your oil.
 

Offline neilep

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Why Does Car Oil Go Black ?
« Reply #2 on: 23/07/2007 23:03:34 »
THANK YOU DAVE....This is very helpful.

So it's mostly carbon from fuel and not wear and tear from the engine , which I thought it might be.

Cheers
 

Offline kdlynn

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Why Does Car Oil Go Black ?
« Reply #3 on: 23/07/2007 23:05:11 »
it's not a good sign if it goes black though... right?
 

Offline neilep

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Why Does Car Oil Go Black ?
« Reply #4 on: 24/07/2007 19:46:26 »
it's not a good sign if it goes black though... right?

I think you're right Kadie....but I think it does eventually go black anyway !!
« Last Edit: 24/07/2007 20:05:03 by neilep »
 

Offline lightarrow

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Why Does Car Oil Go Black ?
« Reply #5 on: 24/07/2007 19:54:06 »
I think the darkening is also due, probably as minor contribution, by tiny metal particles from the engine.
 

Offline neilep

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Why Does Car Oil Go Black ?
« Reply #6 on: 24/07/2007 20:06:36 »
I 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 ?........
 

Offline lightarrow

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Why Does Car Oil Go Black ?
« Reply #7 on: 27/07/2007 22:19:09 »
I 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 ?........
Yes.
 

Offline Bored chemist

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Why Does Car Oil Go Black ?
« Reply #8 on: 28/07/2007 16:49:39 »
In the good old days the lead in petrol (gasoline) would make a contribution too.
 

Offline chris

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Why Does Car Oil Go Black ?
« Reply #9 on: 28/07/2007 17:41:05 »
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

 

Offline lightarrow

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Why Does Car Oil Go Black ?
« Reply #10 on: 29/07/2007 11:20:07 »
Thank you Chris!
 

Offline neilep

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Why Does Car Oil Go Black ?
« Reply #11 on: 29/07/2007 15:56:35 »
Yes, thank you very much Chris.
 

Offline Karen W.

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Why Does Car Oil Go Black ?
« Reply #12 on: 29/07/2007 17:22:38 »
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



Chris I did that with my new lawn mower and it wouldn't start anymore I took it to the shop and the guy told me I flooder the oil filter and some case thing he had to replace the filter , gave it to me to take home and clean then put a new one in. LOL he also had to clean the carborator I think it was as it filled with it!
 

Offline Simulated

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Why Does Car Oil Go Black ?
« Reply #13 on: 29/07/2007 17:26:53 »
This would be the question for my dad. He was a mechaic for 15 years. I'm sure he could tell you EVERYTHING about oil and cars. LoL.
 

Offline Karen W.

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Why Does Car Oil Go Black ?
« Reply #14 on: 29/07/2007 17:27:10 »
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 ?

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!
 

Offline neilep

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Why Does Car Oil Go Black ?
« Reply #15 on: 30/07/2007 03:15:35 »
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 ?

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!


Me ?.....change oil ?....me ?......


Me gets subordinates to do that !!...it's tuff enuff having to fill my own car up with petrol !!...sheesh !!!
 

Offline Karen W.

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Why Does Car Oil Go Black ?
« Reply #16 on: 01/08/2007 14:45:35 »
All done!
 

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Why Does Car Oil Go Black ?
« Reply #16 on: 01/08/2007 14:45:35 »

 

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