Does oil breakdown?

I've been told that oil can breakdown, isn't that why we change the oil?

What do you think?

From what I've read, oil is oil, and doesn't change over time. What DOES change is the additive package and the viscosity index improvers. 10W-40 may "shear back" to a 10W-30 or a 10-W20 weight oil. Multiviscosity oil is made by adding chemicals which cause the thickness of the oil to remain thicker than it otherwise would be with increasing temperature. The problem with internal combustion engines is that they start with zero oil pressure at ambient temperature, which can be -40* or lower, and are expected to run at temperatures between 180* and 220*. The oil is thick when it should be thin, and thin when it should be thick. Viscosity index improvers mitigate this problem, but they don't last forever.

Another issue is the TBN, or total base number. Combustion products are generally acidic. In order to keep the acid, which winds up in the oil, from attacking the bearings and other metallic parts of the engine, oil formulators add buffer salts to keep the oil from getting acidic. Those buffer salts get used up over time, and the oil's ability to neutralize engine acids disappears.

Some large ships never change the oil. They continuously monitor the oil's chemistry, ensure it is filtered properly, and add whatever is necessary to the oil to maintain the right numbers. If you're willing to do that, you can extend the life of your oil substantially.

LWG has nailed it very well. Oil doesn't break down, but the important additives in it do. There are around 7 additives in most oils, all designed to make oil perform way beyond its basic abilities.
Viscosity Improvers are long-chain polymers added to the base oil product to keep the viscosity stable over a wide temperature range. Oils with large amounts of VI's are known as multi-grade oils.
Anti-wear additives are used to counter wear on engine components. These additives can range from zinc and phosphorous compounds that form chemical bonds on metal surfaces to reduce spalling, through to simple additives such as graphite and molybdenum compounds that increase lubricity.
Anti-corrosion compounds are designed to chemically react with corrosion-causing chemicals, created by the combustion process, to neutralise them.
Anti-foaming additives are added to oils to reduce the tendency for oils to foam, when being thrashed around inside high-speed rotating components.
Oil contains chemical dispersants that stabilize contaminants, and prevent them from agglomerating and separating from the oil to form dirt buildup.
Oil contains detergents that neutralise oxidation by-products, and which keep engine internals clean. Some detergents are in the oil naturally, and some are added.
Oil has Oxidation Inhibitors added to prevent oxidation, which produces acid, sludge, varnish, thickening and decomposition of the oil. Oxidation is caused by high temperatures, reactions with free oxygen and nitrous oxide, and chemical reactions caused by unstable metal ions. Oxidation destroys oils ability to lubricate properly.
Oil contains Friction Inhibitors that are in the form of straight-chain and fatty-acid molecules. These chemicals work to reduce friction between any two metal surfaces that are sliding or rotating against each other.

So, you can see that oil is a complex mix of many chemicals, which are broken down by heat, by corrosive by-products of combustion, by oxidation, by other unstable chemicals, and by reaction with unstable metal ions that are basically free-radicals looking for a chemical reaction to stabilise their structure. Once they react with chemical additives in the oil, new compounds are formed, which are usually undesirable to keep in the oil.
Thus, we have a need to change oil regularly to remove the contaminents, and replace the additive levels in the oil.
Filters remove the larger sized particles of contaminents, but only fresh oil removes all the nasty buildup of undesirable chemical compounds, that are created by heat and the combustion process.

Used oil can be re-refined into new oil, via treatment in a complex process that removes all the contaminents, and which adds new additives to bring the chemical structure up to the equivalent of new oil.
However, most re-refiners do not treat used oil adequately to ensure it meets the standards of new oil, due to the high cost - and as a result, re-refined oil is looked down upon, by most end-users, as a sub-standard product.
Nowadays, most used oil is refined into bunker oil for burning in ships engines, by merely cleaning the major contaminents from it.

I was going to start a thread about oil but thought this one was appropriate. I've always used Shell Rotella in all my trucks and machines and buy it by the 5 gallon pail. Today while getting some filters for oil changes, I noticed that Delo 400 was substantially less than the Rotella. I think I recall reading somewhere that an engine will become "addicted" to the additive package for a certain brand oil and switching oils can increase internal wear. Does anyone have experience in this or heard the same thing. I bought the Rotella just to be safe but at the discount offered for the Delo, it would have saved me at least a Ben Franklin today.

i can tell ya from experience (when I was much younger and didn't know better) that if you do not change your oil as required, it will form to a thick sludge over time and will not circulate, lube and cool the engine and it's parts like it was designed to do thereby seizing the motor. Been there and done that. I also learned a lesson from it. A one time expensive lesson for me.

Dig_Texas - Once you've been running on a certain brand of oil, swapping to another brand can sometime cause problems, such as increased oil consumption. In the 1970's, we found that Cats didn't like Mobil brand oil.
If someone using a Cat swapped over to Mobil brand oil - as I and other local contractors did - we found that oil consumption increased substantially.
When running on Mobil oil, blue smoke was regularly visible from good condition engines exhausts, when idling, and oil consumption would often double or triple.
We never found out what it was about Mobil oil that caused this problem, but I suspect the Mobil oil additives package, contained an additive that lubricated the cylinder walls too well, and allowed too much oil past the rings.

It's reasonably well-known that changing over to a high-detergent oil from a low detergent oil will strip much beneficial carbon from sealing surfaces and piston ring grooves, thus leading to increased oil leakage and oil consumption.

I'm unable to understand why the Delo 400 was "substantially" cheaper than the Rotella. Both are well-known and well-respected brands, and I couldn't imagine that either company would shortchange users on the additive package.
However, new additives are constantly being discovered and added to oils, and perhaps a new, cheaper additive has been found for the Delo, thus reducing its manufacturing cost. However, companies usually brag about "new" additives when they're added.

The only other reason I could envisage for the low price for the Delo would be the oil company or a distributor doing a special deal on a product that was in oversupply - and they needed to move their oil stocks that weren't selling fast enough.

I always found that talking to other users in your line of industry soon cuts through the oil companies advertising BS, and claims - and the end users give you far better feedback on what kind of performance they're getting from the particular brand of oil they're using.

OzDozer Im pretty confident that the problem with the Mobil oil was that it was a synthetic. When running a type 2 mineral oil it is very common to get paraffin wax built up. Usually this does not harm anything but when the wax builds up on seals it can make an artificial seal of the wax. When you switch to a cleaner oil, Mobil in this case it can clean up the old wax or other sludge, freeing it up and sending it through the engine to eventually smoke. Sometime this will cause leaks or other issues. Of course leaving the wax in an engine will cause other problems down the road but it wont show up in a fleet like changing you saw when changing oil brands.

This is just one scenario

Dig Texas your engine doesnt develop a addiction but there are lots of misconceptions about oil and changing oil brands. Most of them come from believing an oil salesmen that wasn't the most honest.

blitz138 - The era I'm talking about with my Mobil oil experience, was the early 1970's - and there were no synthetic oils on the market in Australia at that time. The synthetic oils did not appear until the late 1970's here.
In addition, all synthetic oils placed on the market were loudly proclaimed as, and marked as, "synthetic". The oils I used in our earthmoving equipment at that time were called "Series 3" oils, and nothing was ever mentioned about any synthetic ingredients.
I used Series 3 multigrade oils, which have high levels of viscosity improvers, as well as high levels of additives, particularly added detergents.

It was interesting in that I used Golden Fleece oil (which was refined by Caltex) for many years, and Golden Fleece oil was particularly good. Many a time, Cat field servicemen remarked about how clean my engines were, when pulled down for overhaul.

However, I swapped fuel agents when I moved to another area, and the Mobil agent won my business as he was local and provided good service. The problems started immediately I commenced using Mobil Series 3 oils.
Speaking to other contractors who were using Mobil, and watching their machines work, showed me that Mobil oil was noted for high oil consumption in Cat engines.
Engines that were using a quart of oil a day on Golden Fleece oil promptly started using a gallon a day when Mobil oil was used. Returning to Golden Fleece oil saw oil consumption drop back to a quart a day.

I also tried Shell and Caltex Series 3 oils, and they provided near-equal performance to the Golden Fleece oil, with no major oil consumption problems. However, Golden Fleece oil kept engine internals cleaner.

OzDozer said:

I'm unable to understand why the Delo 400 was "substantially" cheaper than the Rotella. Both are well-known and well-respected brands, and I couldn't imagine that either company would shortchange users on the additive package.

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Not sure why but the Rotella was priced at 17.99/gallon and the Delo at 12.99. I think I'll stick with what seems to be working. None of the machines use enough to add between changes and the SOS comes back good.

No, Oil gets dirty but it does not wear out. This fact is substantiated by the U. S. Bureau of Standards, the Shell Oil Company, the U. S. Air Force, and many others.

OzDozer Im sorry I didnt see you were talking about 1970s.....


Oil absolutely does break down over time. There are several things that can happen to an oil in engines, gear boxes, or any other application. alanmurfee unless you can post a link from the US Bureau of Standards, Shell, Air Force, I can not believe this.

In almost every oil there are additives to combat oxidation. What most people think of oxidation is rust...... Oil does oxidize, so not only is it being broken down it is changing the molecular structure of the oil. Put a oil in a clear bottle and leave it in the a sunny window for 2 weeks you will see the oil change in color, smell, and if you have it tested you will see viscosity change as well.

Oxidation is only one way that oil can change, there are plenty more.