First oil change smells like gas

Yes that’s one of the reasons, even heat cycles alone oil will change color somewhat. Basically listing a few but not all reasons oil becomes darker. Oil can be dark and clean, and still have lots of life left

 

You all got it to some extent.
Here's why:
The filter in your truck can only filter down to about 6-7 micron. Plenty good for those actual metal particles that can damage your engine which are between 15-70 micron. Smallest dot you can see is about 40 micron.

The clearance between piston rings and cylinder is 22-30 micron, which is where most damage will occur other than normal wear and tear.

Now, the oil does not get dirty per SE and it does not "cook" unless something bad happens and then you have worse problems.
The oil turns black because of the soot from the combustion cycle. Those little particles are only 1-2 micron! So, as a wear particle, they are not even mentioned. But because they are so small, they cannot be filtered out! And, while one is not a problem, millions will eventually cause sludge, which is why you have to change your oil every now and then.
That is why oil turns dark, it is normal in every combustion engine. That is why you have to change it, to prevent sludge build up. The filter does it's job of getting the actual wear particles out, which is why you have to change the filter.
Imagine this... If you were a soot particle, and you walked down a huge hallway that was 27 times wider than you, is there any danger of you hitting the wall and scraping it?
Now if you were a wear particle, it is like sliding between two vehicles that are less than a foot apart and you are wearing sandpaper blue jeans.
Oil companies won't tell you this and people who stand to make money for frequent oil changes won't tell you this but, this is how it works.

For me, changing oil every 10K is fine to prevent sludge build up and filter every 10K to get rid of wear particles.

For comparison, bacteria particles is about 4 micron lol.

 

Yes, I would consider soot part of the contamination that the oil is cleaning for sure. You’re absolutely correct that the filter only filters down to a certain size particle and everything smaller will continue in the oil system. I found this article from Amsoil informative. https://blog.amsoil.com/why-does-motor-oil-turn-black/amp/
It has a great illustration of micron sizes, it also speaks specifically to soot.

 

Let me blow your mind for a minute, and you will see why I laugh at these threads.
In real life, I design high pressure hydraulic systems. They get hot, they are under immense pressure, just like in an engine. The difference is there is no combustion cycle. Now, engine oil can be used as hydraulic fluid, just match up the viscosity. Hydraulic systems have a strict filter change timeline, but the fluid can be used thousands of hours! And it is still clear!
Soot is why engine oil turns black. Oil changes just get rid of the soot. See why 10K is no big deal?

 

I’ve also worked extensively for decades with many different types of hydraulic fluids and oils. A standard hydraulic fluid is different than a standard motor oil. Yes it can be used as a hydraulic fluid, any fluid can be made of many different things and can be mineral based or even water(seldomly). A hydraulic system is simply using a fluid under pressure in a confined space to perform a mechanical operation.

So no mind blowing here sorry. I guess perhaps you may know more than Amsoil. I never said that the sole reason behind the dark color to oil was heat cycles by merely a contributing factor that can cause oils to change colors. Nor did I state color was a reason to change oil.

 

They don't even make a conventional passenger car oil anymore. They're blends even if it doesn't say so. Only way to get a conventional is to go with something like Rotella T4 10w30 or 15w40, well that and break in oil.

EDIT: Hell, the Rotella might not even be full conventional anymore.

 

You can buy full synthetic hydraulic fluid with the same anti wear and anti foam additives. Only difference is combustion in engine.
My point... No dirt is the cause of darkening. No wear metals is the cause of darkening. No heat is the cause of darkening as hydraulic fluid reaches same temp. Soot. 1 micron, sludge causing soot is why to change engine oil fairly often.

 

Well that’s what is great about this life, we are all able to form our own opinions. You have yours and I have mine and scientist have theirs. Everyone believes they’re right.
I believe based on what I’ve seen that oil can change color with heat. Oil can change color with contamination from whatever source be it soot, dirt, air contaminates…many things can be a source of contamination.

With that being said, have a great rest of your day as this conversation will go nowhere as it seems you cannot seem to realize heat cycles can discolor oils.

 

Darker colored oil does not necessarily mean it's bad or need changed. It's doing its job keeping the contaminates in suspension. If everybody changed oil by color alone they'd be doing some pretty frequent changes...

 

Truth

 

The average vehicle owner doesn't get that deep into the science of it. I'm just a dork/nerd

 

Yes it’s all very interesting and apparently it’s a hot topic! I wasn’t expecting a debate on the color of motor oil today really.

 

Lol no opinion, just fact. Prove me wrong.

 

I’ll side with Amsoil over some random self proclaimed “expert” on a forum. I’ve sited studies with links and you’ve sited yourself…so your opinion. Comparing a fluid made for engine oil purposes and a fluid made for hydraulic purposes is like comparing apples and oranges. They’re different and exposed to different stresses and contaminates. Good luck with life!

 

Back in the early 80's i was invited to see intercontinental lubricants facility where spectro oils are blended, and tested at their labs here. I got the whole low down how they developed their 2 stroke synthetic lubricants, and saw how they tested them in the lab while claiming their synthetic was superior to the current dino stuff out there. For the 2 stroke motocross industry, this was fairly new technology.