why does oil get dark?

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700
Location
USA
Is it because it is holding all the junk and crud in suspension? Then does clean oil after many miles mean the contaminates are still inside the engine as sludge or deposits? Dark oil would be good - right? This means it is doing its job.
 
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3,321
Location
Bolivia
Yes and No to your ending question. It is good that an oil gets dark from suspending and cleaning (to a certain extent) the soot and contaminants, just like it is good to see dirty water coming out of the clothes washer, indicating the dirt came out. But oils get dark from oxidation, overheating, overstressing, and other things. I was given a very dark oil to analize the other day because it couldn't go past 500 hours in a hydraulic press at 4500 psi. The oil was a turbine oil. Never to be used over 1000 psi. The ability of an oil to hold that "crud" in suspension without clogging the filters or causing wear is what you get from the better oils and especially the better base oils.
 
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531
Location
Columbus, Ohio
Mineral based oils will darken just from the normal oxidation process and exposure to heat. And yes, darkness to a degree is good, saying that the oil is cleansing and carrying the contaminants so they may be filtered by the oil filter system and not depositing varnish and sludge in the engine internals. However, Black, as in diesel is an indication of soot and is indicative of an engine with a problem or either too much fuel or not enough air and needs to be corrected.. George
 
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3,845
Good points all, Add the fact that Organo-metallic EP additives are heat activated and as such upon contacting the hot engine internals will darken significantly making new oil look "old" or used. New Ester EP's do not discolor as much.
 

MolaKule

Staff member
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21,600
Location
Iowegia - USA
Here is a simple way to look at oil darkening. Take a steel plate, put an SAE 30 SA oil on it and rub it with #400 sandpaper. The oil will darken right away because its opacity is increasing (or transparency decreasing) due to particles suspended in the oil. Oxidation by-products such as sludge and varnish, dirt, and fine metallic particles all contribute to the oil's darkening. Detergent/Dispersant packages clean and disperse these products and hold them in suspension. The greater the suspension or "loading" the darker the oil.
 
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2,095
Location
IL
I understand all that. But what I don't get is why one would become darker than another after same time. I know Terry explained it but what I have seen is the oppossite. Castrol GTX 10w30 in a 00 Jimmy w/50k miles pretty clean and amber looking after 3k miles. Switched to M1 SS 10w30. Became dark rather quickly. Maybe GTX seals the rings better somehow? Because it also had no consumption where SS had over 1/2qt in 2500mi. Maybe it's the SS's lighter molecules burning up and leaving that? [Confused] And with Red Line in my car I have significantly LESS consumption than M1, BUT it seems to have gotten darker much faster. Opposite of w/ Jimmy, so consumption and darkening aren't linked. [Confused] [I dont know]
 

Patman

Staff member
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21,989
Location
Oakville, Ontario
Jason, maybe the Castrol GTX was leaving behind some deposits, and the switch to Mobil 1 cleaned them up? Say what you will about M1, but the stuff does keep engines pretty clean. I've seen it first hand myself.
 

MolaKule

Staff member
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21,600
Location
Iowegia - USA
Jason, Since you are running the same viscosity, I would have to say its the detergency differences between the two oils. I have observed what Patman states, Mobil 1 (and Amsoil) have high detergency levels, which I attribute to the esters and their additive packages. While synthetics will not completely clean an engine of dino crud, it will lift and suspend some deposits and turn dark rather quickly when used immediately after dinos. The only timer I experience blowby, is when I go to the 5W30 in my vehicles. These oils do turn darker much quicker than the old standby 10W30 that I use.
 

JonS

Thread starter
Messages
700
Location
USA
That is what i have figured is happening. Castol GTX and Valvoline stays clear longer. Mobil, Havoline, and Citgo get dark very fast. I believe Valvoline and Castrol would leave behind deposits if it is not in the oil - right?
 

Patman

Staff member
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21,989
Location
Oakville, Ontario
quote:
Originally posted by MolaKule: The only timer I experience blowby, is when I go to the 5W30 in my vehicles. These oils do turn darker much quicker than the old standby 10W30 that I use.
Why is this happening? Is it because the 5w30 is thinning out faster than the 10w30, and so the 5w30 is not allowing as good of a seal? (more fuel past the rings?)
 
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2,095
Location
IL
quote:
Originally posted by Patman:
quote:
Originally posted by MolaKule: The only timer I experience blowby, is when I go to the 5W30 in my vehicles. These oils do turn darker much quicker than the old standby 10W30 that I use.
Why is this happening? Is it because the 5w30 is thinning out faster than the 10w30, and so the 5w30 is not allowing as good of a seal? (more fuel past the rings?)

I think it's because the 5w30 shears down under stresses in the cylinder wall, thus allowing more blowby...particles in blowby become suspended in oil...oil gets darker faster. That my theory anyway
 

MolaKule

Staff member
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21,600
Location
Iowegia - USA
I agree with Jason. Thinner oil on cylinder liner (wall), rings don't seal as well as with a thicker oil, more blow-by, more carbonized particulates in oil, oil turns blacker - sooner! White man go across creek, get wagon stuck in mud... Indian lift wagon out of mud... [Big Grin]
 
Messages
349
Location
Quebec, Canada
quote:
I agree with Jason. Thinner oil on cylinder liner (wall), rings don't seal as well as with a thicker oil, more blow-by, more carbonized particulates in oil, oil turns blacker - sooner!
This is going against by what I'm experiencing though. Delvac1 5W40 is getting darker faster than Tech2000 synthetic 10W30 in the same amount of mileage...just weird I tell ya! [Confused] Oz
 

Patman

Staff member
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21,989
Location
Oakville, Ontario
Oz, that's because Delvac 1 has a LOT of detergents in it, way more than Tech 2000 Synthetic for sure. Remember, Delvac 1 is a diesel oil, and needs more detergents as a result, so it will clean your engine of old deposits quite rapidly.
 
Messages
349
Location
Quebec, Canada
quote:
Oz, that's because Delvac 1 has a LOT of detergents in it, way more than Tech 2000 Synthetic for sure. Remember, Delvac 1 is a diesel oil, and needs more detergents as a result, so it will clean your engine of old deposits quite rapidly
Yeah, which is making me wonder if I should even try AMSOIL or Schaeffer 5W30 this winter. The other post regarding the use of 5W40 for engine longevity has gotten me confused. [Confused] Oz
 
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3,321
Location
Bolivia
I put Delo in a potential customer's trash truck, and left his regular oil in another. After 611 hours he insisted that his regular oil was better than Delo because it was still amber in color and Delo was black. Analisis showed that Delo still had 2800 ppm of Calcuim and his regular oil had 70 ppm. The Delo also still had over 1300 ppm each of phos and zinc while his regular oil had less than 60 ppm.
 
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