Oil Change intervals

Could oil possibly degrade without changing color.

Yes. To make this simple, I’ll quote from “Bob is The Oil Guy”. I recommend that you visit his site,

"How does an oil ‘lose’ some of its viscosity in a engine?
Shear stability is a measure of the amount of viscosity an oil may lose during operation. Oil experiences very high stresses in certain areas of the engine such as in the oil pump, cam shaft area , piston rings, and any other areas where two mating surface areas squeeze the oil film out momentarily . Most multigrade engine oils contain special types of additives, called Viscosity Index Improvers, which are composed of very large, viscosity-controlling molecules. As the oil passes through the engine, these molecules are permanently sheared or torn apart over time, causing the additive to lose its viscosity-contributing advantages which reduces the oils ability to maintain its higher number. ie… 10w30 ,

Synth Oils do not rely as much on special Viscosity Index Improver additives and will experience little permanent viscosity loss.

The shear stability of an oil is measured by using both ASTM test methods D445 and D5275. First, the viscosity of an engine oil is measured. Then, the oil is exposed to severe shearing conditions by repeatedly pumping it through a specially-sized diesel fuel injection nozzle at high pressure. After shearing the oil, its viscosity is measured again. The percentage of viscosity lost is determined by comparing the second viscosity measurement with the original viscosity measurement.

Although there are no specifications indicating required levels of shear stability for engine oils, lower percentages mean that an oil is more shear stable and will retain its viscosity better during operation."

The aforementioned degradation does not discolor the oil. It is IN ADDITION TO those elements that do discolor the oil.

And then there’s also depletion of the detergents and the barrier additives. See the referenced site for a better understanding. Depletion of additives does not change the color of the oil.

So yes, the oil can degrade without changing color.

If you drove a diesel like I do, you would never know by looking at it. It is black in about 60 seconds in a diesel.

From my experience working at quick lubes, some cars would come back after 3000 miles with new looking oil, and others the oil would look black on the dipstick even immediately after changing it. The viscosity of the oil can change simply through use (i’m referring to shearing), this would not affect the color of the oil.

It has been scientifically shown that the color of the oil has nothing to do with the actual condition of the oil and the protection it offers. As the same mountainbike pointed out, all of this information is available on the bobistheoilguy.com website.

So, Frog, it will only cost you around $30 to find out. Blackstone. These guys, while being very knowledgeable for the most part, do not know if your oil has sheared. They are only telling you it could shear without changing color. Not that it has, because they don’t know and can’t know.

If you want to know, Blackstone, then you will know who is blowing smoke here. It might even be me.

I did Blackstone last year, and learned for my car and my driving pattern, my Mobil-1 EP is good for 10K miles. Period. No more guessing. I choose to change it at a bit over 8,000 miles for a safety factor.

When I get the appropriate mileage on the current EP, I am shoving in Quaker State dino and will run it 5,000 miles, only 5,000 miles because I am guessing dino is not as good as synthetic, and I am going to find out if those who say synthetic is no better than synthetic are correct. I don’t think so, but I am guessing when I say that, so I am going to find out.

Blackstone and stop guessing.

bobistheoilguy is a site for people who are obsessive-compulsives about oil…Shear stability and viscosity index stability were problems that were addressed and solved in the 1960’s…

Most oil turns from tan to brown around 3500-4500 miles…That’s when you change it…

I’ve never given Blackstone a dime and have never had an engine problem owning many, many cars and trucks. I change the oil every 3500-4500 miles and sleep soundly at night…It’s not rocket science…


One possibility that could degrade oil without changing its appearance is contamination with raw fuel.

More likely with a carburetor and a short trip driving style.

I think the more important question is “Is dark/dirty looking oil worn out/need changing?”

My answer to that is no, modern detergent oils are made to suspend dirt/impurities until changed, and can be fine even if they don’t look ‘clean’. This is true especially in older engines.