How long a Fully Synthetic Engine Oil 5w-40 can last?

Discussion in 'Free Thoughts' started by Saint, Mar 7, 2016.

  1. Saint Valued Senior Member

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    How long a Fully Synthetic Engine Oil 5w-40 can last?
    In car forum, some said that 20k miles.
     
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  3. exchemist Valued Senior Member

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    It might, if it is a well-formulated product and your car is in good condition (i.e not stressing the oil too much with contaminants). Truck engine oils often last 500hrs, which at an average speed of 40mph would be 20k miles. Car engine oils I think are more generally are expected to last about half that time, but a good synthetic might do 500hrs.

    One issue limiting engine oil life in cars however is the buildup in the oil of potentially carcinogenic contaminants from partly burnt fuel. I have been retired from the lubes business for several years now, but I seem to recall my automotive colleagues saying that this was becoming a limiting factor (safety in car workshops etc), even though the oil itself could go longer.

    But don't assume all "synthetics" are equally good. A lot depends on the additive inhibitor system used and this varies quite a bit. Better to go on the oil classifications complied with and the specs met by the oil - that is a better guide to performance than just whether a marketer claims is it "synthetic".
     
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  5. Saint Valued Senior Member

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    I Malaysia, usually the workshop will suggest us to change the 5w-40 oil after 10000 KM,
    is that a waste?
     
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  7. zgmc Registered Senior Member

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    I am not comfortable going anymore than 5-6K miles between oil changes. I've pushed 10K before and the oil starts looking pretty dark at that point. If you want to learn more than you need to know about oil, check out bob is the oil guy with Google search.
     
  8. timojin Valued Senior Member

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    [


    WHAT IS THE BASE of the synthetic oil ( the bulk of or hydraulic oil ). is it mineral oil and adjusted for viscosity and others ?
     
  9. exchemist Valued Senior Member

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    "Synthetic" in this context usually implies a hydrocarbon base stock made by synthesis rather than by separation and purification of crude oil, which is what a "mineral oil" is. Typically such synthetic base stocks contain fewer hetero atoms and fewer unsaturated bonds than a mineral base oil. This gives them weaker uninhibited oxidation stability than a mineral base oil (fewer natural antioxidant species present, such as "beneficial sulphur") but better response to antioxidant additives.

    A multigrade made from mineral oil relies on a thin base oil (to give a low enough viscosity for engine starting at low temperatures), chemically thickened with a polymer to give a sufficiently high viscosity at the high operating temperature of the engine in service. Such formulations can be a bit volatile - the light ends of a thin base oil can evaporate over time, leading to thickening and a degree of oil consumption, resulting in a need to "top up" the engine. Furthermore the polymer is a source of chemical instability, leading to engine deposits, and also can be mechanically sheared in service, leading to loss of performance. So "traditional" multigrades are a bit of a compromise, requiring ingenious formulating strategies to minimise the defects while maximising the benefits.

    Synthetic base stocks, however, have a naturally high viscosity index (a high index means that viscosity falls less rapidly with increasing temperature than something with a low index). This allows a multigrade oil to be formulated without a viscosity index improver and without depending on potentially volatile thin base oil.

    These I think are the main advantages of synthetic engine oils. But they do need to be properly formulated, since if they are not inhibited correctly they can degrade really fast in service due to their lack of uninhibited stability, once the antioxidant has been used up.
     
  10. exchemist Valued Senior Member

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    Depends on the car and the driving cycle. Personally I do not think 10k is too unreasonable, since it gives a good safety margin if either of these is stressing the oil a lot. And don't forget it may be that this also limits the potentially carcinogenicity of the used oil, which is safer for the workshop operators who have to work with this stuff all day long! But it may be on the conservative side.

    I would never want to contradict what the engine maker's manual recommends, since this might risk voiding warranties.

    P.S. What may come as a surprise to some is that so-called "Aunt Minnie" driving, in which the engine never gets really hot, and spends a lot of time idling, can be more stressful for the engine oil than motorway driving. This is because you get condensation, unburnt fuel and combustion acid components accumulating. The occasional blast down the motorway can be good for the engine and the oil.

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    Last edited: Mar 8, 2016
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  11. exchemist Valued Senior Member

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    Oil being dark is not in itself an issue. A dark oil is dispersing the products of combustion (it is mostly soot) safely and preventing them from depositing in critical parts of the engine. (Engine oils are full of detergents and dispersants to enable them do this.) Most engine manufacturers today will I think recommend drain intervals that correspond to about 250hrs engine operation - more in some cases. But I may be a bit out of date now - I retired from the industry 4 years ago and it moves on quite fast.

    This site gives an idea of VW's recommendations (I drive one myself): http://www.oilspecifications.org/articles/vw_motor_oil_specifications_explained.php
     
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  12. cosmictraveler Be kind to yourself always. Valued Senior Member

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    I don't use synthetic oil because I prefer to change my oil and filter at every 6 months which is also about 4000 miles or so. This way any particulates that are deposited in my filter will be disposed of and keep the filter fresh and clean. I just have been use to doing this type of maintenance through my lifetime because I can also look around under the car and check for anything else that might be wrong or leaking. I also rotate my tires at the same time as they do this for free since I'm getting an oil change and the car is already on the lift. I'd rather change the regular oil so that it won't lose its viscosity in those 4000 or so miles and keeps my engine very clean internally. It is up to you to do whatever you want to do with synthetics but changing the oil at closer intervals will be better for the car in my opinion and could prevent other problems that might be happening under your car.
     
  13. timojin Valued Senior Member

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    You have written to me as a supplier to an ignorant consumer .
    Mineral oil to my understanding are all petroleum products . and different cuts are taken during separation, and viscosity can be adjusted on different cuts . I am sure if you have worked in lubricants you are aware of that . Let me fill you in . At some time it was pursued in using polyglycol ether to substitute mineral oil , so I was thinking perhaps that is why it was called synthetic, but as you pointed out is about the same crap. just a sofistc name to impress the consumer and charge him a higher price. The extreme pressure is the same , the corrosion inhibitor is the same . so tell what else is new.
     
  14. exchemist Valued Senior Member

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    Eh? I was trying to answer your question. But it is true I assumed no specialist knowledge on your part - and it looks as if I was right to do so.

    I have explained the advantages of synthetic hydrocarbon base oils (often called poly alpha olefins, PAO), as these are the most commonly used in engine lubricants, which is what this thread is about. Your jeering remark that these are the "same crap" as mineral oil, and basically a scam to charge a higher price for the same stuff, is bullshit. PAOs are considerably more costly to produce than mineral oil and have real advantages, some of which I have outlined.

    Your comments about extreme pressure agents and corrosion inhibitors are on aspects that I did not discuss. That is because these are not particular challenges for engine lubricants at present and consequently the choice of synthetic base stock is not intended to address these aspects of performance.

    If you want to learn more about this subject, you could try reading this on the various types of lubricant available: http://www.globalspec.com/learnmore...oils_fluids/synthetic_oils_greases_lubricants

    By the way I am getting fed up with your hostile attitude. To respond in kind, I will observe that I am still waiting for a subject to come up in which you do not at some point reveal yourself to be an ignoramus with a chip on his shoulder.

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  15. timojin Valued Senior Member

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  16. timojin Valued Senior Member

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    I might be ignoramus But will accept intimidating BS, I don't have to read your reference and indicating me what what to learn , I have my own books on lubrication , I have worked on the subject and developed some formulations which are used. So getting back to lubricants . Normally the big culprit is the moisture that permeate into the carrier and the extreme pressure additive get decomposed and produce corrosion in the cylinders . I am not sure if the so called dirt is the big culprit . You have to keep in mind the surface roughness of the cylinder walls and some impurity are beneficial . To refresh your memory , at some time in the 1970 they added graphite into the motor oil. which I believe it smoothened the surface roughness on the cylinder wall.
     
  17. timojin Valued Senior Member

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    I believe some carbonaceous dirt is good for the engine. It sound bad , I change my oil between 20 and 30000 milis I have driven my cars over 150000 miles , the engine is good but the body is damaged by poor paint job of some car maker like Mazda at the present 1o years and corrode ol over Honda have a good paint job. good
     
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  18. Sylvester Registered Senior Member

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    I did the same with an old car i had and the car ran great, way over 100,000 miles on it.
     
  19. exchemist Valued Senior Member

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    This is crap from start to finish, unsurprisingly. Almost all motor oil formulations today are designed meet specs from engine manufacturers. Moisture and byproducts of ZDP (the type of EP agent used in most motor oils) simply do not feature among their concerns.
     
    Last edited: Mar 8, 2016
  20. timojin Valued Senior Member

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  21. timojin Valued Senior Member

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    Sorry old guy, for in a way hijacking the tread . I just like to talk a little more on chemistry then standard consumer talks. I know you are a English gentleman and you are a very proper composed individual.
     
  22. Oystein Registered Senior Member

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    WWJD?
     
  23. Oystein Registered Senior Member

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    Exchemist has forgotten more about chemistry than you ever knew.
     

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