Why does oil get dark?

[chinee]

I've been reading and learning for about 2 months now and I have to say thanks for the education! I've also searched but can never seem to find a discussion that addresses this.

I've used GTX forever and always notice that the oil begins to darken almost right away. By the time it gets to 3-4K, it's black, however, wiping the dipstick leaves a dark brown oil stain, so I know it's not really black.

Is it soot? How does this affect the performance of the oil? Should I be concerned?

Any help will be appreciated.

 

[Ray H]

The darkening results from suspended particulates too fine to be trapped by the filter. This is a good thing because it's graphic evidence that shows the detergent/dispersant package is doing its job. Particulates this small are also thought to be too fine to cause bearing wear since they bounce off the bearing surfaces in the oil film instead of grinding away at them. This is crud that would otherwise be happily forming sludge and varnish deposits, and, yes, soot is definitely one of the components.

 

[Bub]

I would also have to agree that soot (blowby) is a major factor in oil darkening. The harder I drive my cars the faster the oil gets dark.
Clay

 

[Dr. T]

Ahhh because it's being "cooked" inside the engine...just like if you were to put it on a frying pan. The "it gets dark because it's cleaning your engine thing" is probably BS as far as I'm concerned.

 

[chinee]

My car is brand new, changed oil at 1200 miles, then 4000 miles (switching to M1 at 7500). Both times the oil was black, so I have trouble believing that the oil gets black cleaning the new engine. And 85% of all my driving miles is highway.

Now maybe if a by-product of combustion is carbon or a carbonized compound (terminology?), and this gets into the oil to turn it black...that sounds somewhat logical.

Dark oil makes me cautious, and I'll tell you, if the M1 turns black really soon, I'll be really nervous leaving it in for 7500K intervals. I do plan on oil analysis at 5K and 7.5K though. Hopefully that'll give me a little peace of mind.

Mr. T, you don't believe the cleaning the engine bit...

what do you think causes the darkening of the oil?

 

[MolaKule]

My Nissan has always turned the oil black within 3.5k, especially when driven hard. I have only used Amsoil or Mobil 1, same for each oil.

It is the combination of partially burnt hydrocarbons and fine metal particles.

The D/D additive in the oil is placing the contaminants in suspension.

 

[Ray H]

quote:

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Originally posted by Dr. T:
...The "it gets dark because it's cleaning your engine thing" is probably BS as far as I'm concerned.

---

"probably BS"? Ok, run some non-detergent API SA oil for 6,000 miles. It'll remain delightfully transparently amber. There - the perfect oil!

 

[Dr. T]

I'm sorry guys...pressed the send button a little quick...just want to clarify.

All oils will turn black given enough time. I've found thinner oils will turn black quicker than thicker ones. While we mentioned that color isn't the be-all-end-all sign that an oil is toast, it certainly is an indication that either 1. it's char-broiling or 2. extremely dirty engine. Either way, there are contaminants and the oil should be changed when extremely dark.

When I switched to thicker oils, the color remained amber longer...ie. it 'held up' longer.

 

[chinee]

quote:

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"probably BS"? Ok, run some non-detergent API SA oil for 6,000 miles. It'll remain delightfully transparently amber. There - the perfect oil!

---

But if it's a new car, what is there to clean? Wouldn't the darkening of the oil now be a result of only "blow-by"?

 

[medic]

quote:

---

Originally posted by chinee:

quote:

---

"probably BS"? Ok, run some non-detergent API SA oil for 6,000 miles. It'll remain delightfully transparently amber. There - the perfect oil!

---

But if it's a new car, what is there to clean? Wouldn't the darkening of the oil now be a result of only "blow-by"?

---

Okay, just to throw a wrench into the works, I had a '84 oldmobile with a 5.0L V8. 100k+ miles and the Castrol GTX was still clear (a few shades darker) when I drained it at 3,000 mile intervals. I never questioned this because I thought it was a GOOD thing.

I wish I could get these results from my '97 Ford.

 

[Al]

My experience with many many cars over many many years

: Vehicles which have loose rings (use more oil) generally cause oil to get darker earlier because of blowby and solids. Vehicles which use almost no oil maintain "cleaner" oil for a longer period of time. Again-just my experience.

 

[digitaldrifter91]

i would be cautious about running oil alot longer if it is getting dark. usually my oil wont get dark till 2k. but with my auto rx...its dark at 800 miles, u can see how dirty my engine is. its something to watch out for.

 

[Ray H]

quote:

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Originally posted by chinee:

---

But if it's a new car, what is there to clean? Wouldn't the darkening of the oil now be a result of only "blow-by"?

Probably, but depending how "new", blowby will be greater until the rings properly seat. (Presumably, you did ease your engine through its initial break-in with reduced power demands and varying your speed frequently for the first 500 or 600 miles.) And, there'd also be more wear metals circulating around during the initial break-in. As other respondents have indicated, when the oil gets really dark, it should probably have already been changed. After all, the D/D package will become depleted, and these relativley harmless unfilterable particles will begin agglutinating into troublesome larger (read, "abrasive") particles. I suppose this issue would further make the case for using heavy-duty "fleet" oils in gasoline engine vehicles. Diesels, due to their inherently much higher compression, definitely have a penchant for blowby, and oils designed for them have a more robust D/D package accordingly. They'll still darken quickly, but they're made to handle the extra blowby. These oils also have a greater capacity to neutralize acids, too, since the diesel fuel in the U.S., at least, tends towards more sulphur content over the past decade.

[ March 28, 2003, 01:49 AM: Message edited by: Ray H ]

 

[metroplex]

Yeah, I varied the engine speeds on my 2003 Ford 5.4L SOHC V8 during the first 500 miles

900 RPM, 5000 RPM, 3800 RPM, 5000 RPM, 1000 RPM, 4500 RPM

:evil:

 

[mracer]

Metroplex...Lightning or Harley? I know what you mean though. Since spring broke out I have been "exercizing" my 400HP and 470lb/ft. I got the red beast sideways

the other day trying to pull out on a busy road.

Dam, I am gonna get myself arrested someday.

"Uh... officer, uh...what did you mean by excessive acceleration...?"

 

[MNgopher]

I think metro has an E250 van with the 5.4! But I'm sure like everyone else he wouldn't mind an L or a Harley!

 

[chinee]

Still unsure of the answer, but one thing I'm certain of is that a couple of oil analyses will help me determine the best change intervals to apply, given the cars I drive and the conditions under which they're driven. Obviously color is an indication of impurities/contaminants in the oil, but does not indicate whether oil is still useful or not.

Managed to slide a length of aquarium air tubing down the dipstick tube of my Sequoia, but can't figure out how to sample the oil on my G35. I'll post a separate topic on this. (don't want to buy a fumoto)

[ March 28, 2003, 09:53 PM: Message edited by: chinee ]