Darker oil faster. Why?

[HawkeyeScott]

I've read time and time again that black oil doesn't necessarily mean an oil is worn out. Got that. But can anyone tell me why some engines will blacken an oil faster than others?

For instance, I'm running dino Valvoline in both of our daily drivers. At nearly the same mileage since the last OC, the oil in the 4.6 Ford motor is still pretty golden in color. The Jeep 4.0's oil is considerably darker. Air filters, oil filters, nor oil seem to make much difference. Driving styles and type of driving are fairly similar too. This seems to be the case all the time. Something seems different in the way these motors "use" oil.

Thoughts?

 

[Quattro Pete]

One thing that comes to mind is engine operating temperatures. One engine may be operating at higher temps than the other. The difference may be just big enough for certain chemical processes to take place quicker in such environment and darken the oil faster as a result.

 

[Laminar Lou]

Does the Ford have a tow package with an oil cooler? I echo what Quattro Pete said. My guess is that the jeep has higher temps that activate the chemistry faster.

 

[benjamming]

add pack can cause color differences & the dye itself can contribute

 

[theedge67]

But the add pack and dye would be the same if he is using the same oil. Unless it is diff. weights, then it could be different.

 

[Black_Thunder]

well engines components vary from one another, especially an OHV Inline Six Cylinder compared to a Modular V8 with SOHC.

 

[redtan819]

Maybe one engine is dirtier than another, or you ride one harder.

I gurantee you that if you put the same oil for 5000 miles in a brand new car and one with 300k miles that the used oil will not look the same.

 

[Ramblin Fever]

Just curious - which engine is typically *harder* on an oil, OHV or OHC engines?

 

[Mr_Incredible]

Perhaps the difference is in the amount of oil that does NOT get changed, making one vehicle appear harder on oil than the others.

You'd have to run each vehicle for a few miles after an oil change and do the drip thing on white paper towels for a comparison.

Just a thought...

 

[TR3-2001SE]

Darker oil faster means fuel is getting in the oil. Car is running rich. Oil will eventually get dark with other solubles and insolubles but if it does it quick it is fuel. My TR3 with SU carbs makes it dark in the first 600 miles.

 

[Merkava_4]

Quote:

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I've read time and time again that black oil doesn't necessarily mean an oil is worn out.

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Doesn't that mainly apply to synthetics? If I was running a dino and it was getting dark on its way to black, I'd be compelled to drain it out.

 

[HawkeyeScott]

The weights are different. Always 10W-30 in the 4.0. 5W-20 or 30 in the 4.6.

And it's not so much that the Jeep's oil gets black unusually fast, it's more that the oil in Crown Vic (LX package, no tow package) stays golden longer than in any car I've ever had.

The fuel in the oil idea is interesting. I had the same Jeep engine in a 1994 GrCh. and that oil consistently had a strong smell of gas to it.

If it's the engines' components that are different, what would those different parts do to the oil?

 

[Merkava_4]

My first thoughts are that the Crown Vic is buttoned up tighter than your Jeep and that's why the oil is staying lighter. But I'm just guessing and really don't know for sure.

 

[wileyE]

Ran a 300 ci ford six on propane and the oil remained absolutely new looking at oci time. It was tempting not to change it. So the darkening must have at least something to due to dirtyness in the combustion of gasoline. Think some of it is also oxidation, like an apple turns dark after it's exposed to air. The oil may turn dark as it's additives nuetralize the acids of combustion byproduct?

 

[Merkava_4]

I'm thinking it's a combination of combustion by-products and dirt that gets passed the air filter. What do you guys think about that?

 

[jmac]

I think if you have enough dirt coming past the filter to change the color of your oil you better get it fixed fast or soon you will have an engine with no compression left.

x2 on fuel causing oil to darken fast, this I think as more a dark brown color, and left a long time can get very dark. However if your oil gets absolutely pitch black, to me that that is soot, or the oil is oxidizing greatly from blow by gasses. It takes very little soot to turn things black. Since it takes so little soot to change oil color, basically acting as a dye, you can have a little soot and have a lot of life left on the oil, or you could have a lot of soot and no time left on the oil, no way to tell once it gets pitch black by looking at it. YMMV, caveat emptor, and etc.

 

[Merkava_4]

Quote:

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I think if you have enough dirt coming past the filter to change the color of your oil you better get it fixed fast or soon you will have an engine with no compression left.

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So you're saying that the "dark oil equals dirty oil" phrase is just a myth? If that's true, then I'm in for a total re-education. All my life I had always thought that very fine particles of dirt that are smaller than what an air filter or oil filter can catch is was caused oil to turn dark.

 

[Quattro Pete]

Quote:

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So you're saying that the "dark oil equals dirty oil" phrase is just a myth? If that's true, then I'm in for a total re-education. All my life I had always thought that very fine particles of dirt that are smaller than what an air filter or oil filter can catch is was caused oil to turn dark.

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The contaminants you're writing about can contribute to oil darkening, but that is not the only way an oil gets to darken. Like mentioned before, additive chemistry in the oil, when subject to high temperatures (like the ones present in every engine), can cause the oil to change its appearance. Other factors like fuel may affect the color as well.

In a diesel engine, an oil will turn dark in a matter of 100 miles. That does not mean that the oil is already dirty and needs to be replaced.

 

[Black_Thunder]

heat could be another factor.


perhaps one runs a little hotter in temp in various parts of the engine.

 

[sw99]

The 4.0L tends to run on the hot side. My 4.0L always has darker oil than my last Ford Modular 5.4L.