Really dark oil - CG 0w30

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May 8, 2009
I just changed my friends oil, he has a 2004 Cobra and ran 6.5qt of GC after running RP 5w20 for the last 2 changes. He always uses a Motorcraft filter The oil had about 4,000 miles on it and was VERY dark coming out. Does this mean it did a good job cleaning or is there something wrong?
You can't judge and oil by it's colour. I have UOA's that show me my oil is spent and the oil is still a nice golden colour on the dipstick then I have others that the oil is very dark within a few thousand miles but the UOA's say it's suitable for continued use!
In most cases yes. If it was a milky brown colour then you have a coolant leak into it. If it's a thick dark brown colour and feels like a paste, then it's a sludge issue. But if it's just "dirty" looking dark then it doesn't mean much.

UOA is the only way to tell how well the oil is doing and how much time it has left.
The only way to tell is to run it a few more times. When I switched to the Amsoil ACD even though the car had relatively low miles, it got dark quickly. It wasn't until the third or fourth change that it stopped doing that. Now it stays pretty much the same out to the 5,000 mile interval, barely darkens at all. The only resonable explanation was that it was doing some cleaning at first.

Edit. I forgot to add, nice car! The '03-'04 Cobra is what I'll probably buy after my TL is paid off..... Just what I need, another toy.
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I use Mobil 1 in all my cars. I have found that it gets dark colored fast in my cars with an iron engine block. My cars with an aluminum block stay honey colored for a LONG time.
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