How long can you avoid changing full synthetic oil


I also believe that, after the wealth of information provided, the OP really does know the answer to his question.
However, I also believe that he is waiting for somebody to tell him that it is okay to ignore the maintenance needs of his car.


I’m pretty sure that’s incorrect. Do you have any proof?

Edit - forget this part: (It’s also incorrect because all oils contain detergents and corrosion inhibitors, that are used up as the engine runs.)


Make sure you read beyond the first line … I also said: “The problem is that there are other additives and they do get used up.”


True, but I’m pretty sure all oils have VI improvers. Any evidence they don’t?


Although some experts feel synthetic base stocks can be used forever, it is well known that eventually the additives will falter and cause the oil to require changing. Moisture, fuel dilution, and acids (the by-products of combustion) tend to use up additives in oil, allowing degradation to occur. However, by topping off, additives can be replenished. Through good filtration and periodic oil analysis, synthetic engine oils protect an engine for lengths of time far beyond the capability of non-synthetics.


Mom said “eat your vegetables” I didn’t know why but did anyway. Mom says “change your oil”. You don’t need to know why.


Who makes this claim?


Molecular Scientists. But you do not have to be a Chemist to know that synthetic molecules do not break down in our life time, just look at plastics … they remain in landfills indefinitely, but not forever.


Synthetics are nothing more than uniform hydrocarbons. That is all. Plastics and synthetic oil have nothing in common, regarding longevity. Synthetic oil molecules are made to carefully specified lengths and branching to maximize their lubrication characteristics. Just replenishing additives won’t get rid of the ongoing buildup of unfilterable contaminants.

Synthetics with extra long change intervals (like Mobil1 “Extended Performance”) achieve that through extra additives to start with.


Again, I am not advocating replenishing additives as an alternative to regular oil changes, but I can say that synthetic motor oils last a lot longer and also have a different filter membrane in the oil filter.

The jury is still out on changing with regular oil more frequently versus synthetic oil changes less frequently in relation to cost. The synthetic motor oils are almost three times as expensive. However, when airplane engines almost exclusively now use synthetic oils it would appear that they are better.


All oils behave differently at different temperatures. As temperatures drop, the hydrocarbon molecules in mineral oils start to line up and stick together. This causes the viscosity of the oil to increase, which makes it harder for it to lubricate an engine. At high temperatures, the opposite happens and the oil’s viscosity decreases, making it less effective at protecting moving parts. Additives knows as Viscosity Improvers are added to combat this. Basically viscosity improvers are coiled molecules that shorten when cold, and lenthen when hot. The short, cold molecules interfere with the hydrocarbons lining themselves up, and the longer hot molecules help things stick together better (at the molecular level) and keep things from getting too ‘loose’. Unfortunately, viscosity improvers break down when exposed to heat and mechanical shearing, so oils that use a lot of viscosity improvers don’t last very long. This is where synthetics have an advantage. The branched-chain structure of synthetic oils naturally resist changes in viscosity with temperature. It’s just the way they’re made. Therefore, true synthetic oils often don’t need any viscosity improvers at all! This is one reason synthetic oils last so much longer than non-synthetics. The physical property used to quantify an oil’s resistance to viscosity change with temperature is known as the Viscosity Index (VI). The higher the VI, the more resistant to viscosity change the oil is. (soutce:


Focus on this line in particular: “Therefore, true synthetic oils often don’t need any viscosity improvers at all! This is one reason synthetic oils last so much longer than non-synthetics.”


In an engine, normal environmental degradation is not the issue. All oils (and viscosity modifiers) breakdown under shear stresses, where the molecules are torn apart over time. 100% pure synthetic Class IV or V oils are much more resistant to shear and thus can last much longer than conventional oils, but not forever.

Because of the higher shear stability of Class IV and V oils, they don’t need to rely on viscosity modifiers. However, as @texases mentioned, many other additives are used, probably in higher concentrations than in conventional oils, to provide extended life. MPT claims their oil can go up to 30k miles between changes (with regular filter changes) under normal conditions, 15k miles under more severe conditions.

People wanting to extend synthetic oil use to the max can use add-on bypass filter systems to further filter the oil, down to 2 microns or so. Amsoil claims up to 80k miles (or up to 1200 hours or 2 years) using certain of their bypass filters. However, oil analysis would definitely be required in this case.


No there isn’t. My wife’s 07 Lexus uses 5w-30 regular Dino oil and my 14 Highlander uses 0w-20 full synthetic. The oil filters are the same part number. I know there are some aftermarket filter companies who make extended drain interval filters for use with synthetic oil. But I don’t know if any OEM filter that’s different.


Yep my filters are the same for dino or synthetic. Actually the cost is pretty reasonable for synthetic now. A couple days ago I bought a 5 qt jug of 0-20 Mobil 1 for $25, a jug of 5-30 Mobil 1 for $25, and a 5 qt jug of jug of 5-30 Mobil dino for $16. So let’s see that’s $5 per quart versus $3.20. Three times would be $9.60 a quart or $48 a jug. Don’t think so. And that’s without the Mobil rebate. Maybe if you compare Mobil 1 to a store brand but that’s not apples to apples.


There are oil filters for conventional oil and synthetic oil and they are not identical for my 2005 Mercedes CLK320. They probably cannot be interchanged safely when the specs tell us to use a different oil filter for synthetic oil. I am not a gambling man with my $ 45000 Mercedes.


The different filter is more likely related to the longer oil change intervals the European cars recommend now, along with the special (high additive) synthetic oils. MB, BMW, and VW have tougher oil specs, many synthetics don’t qualify for use in those cars. So if the car’s expected to run 10k+ miles between changes, then a higher capacity filter would be in order.


I have to agree with @texases

The ones for extended oil change intervals are fleece-lined, and slightly more expensive

The others are not fleece-lined, and are cheaper. If the cheapos are used and left in there for extended intervals, they can literally disintegrate over time. I’ve seen it myself, a few times

The fleece-lined are not higher capacity,

And they are filter elements, not spin-on filters, for anyone else reading this

They’ve been around since the late 1990s, nothing new here


Still not sure about the long interval filter. Again - wife’s Lexus uses conventional oil with a change interval of 5k miles. My Highlander uses full synthetic with a recommended change interval of 10k miles. The filters are exactly the same.


That’s true of turbines almost from the beginning, but piston aircraft engines rarely use synthetic.