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are molecules of mineral oils thicker than those in synthetic oils ? #5234673 10/09/19 09:10 AM
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Gummybear Offline OP
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Hi Guys,

my 1993 Harley Davidson sportster needs about 1 liter 20W50 Castrol Synthetic Oil every 625 miles ( 1000 km ). This is too much ( twice what could be considered as normal ). The person who sold to me this motorsicle says "it is because you use synthetic oil".
What do you think ? Will the use of mineral oil with the same viscosity 20W50 decrease the oil consumption ?
If yes, I would be pleased if someone could explain why ?

Thanks

Regards

Gummybear

gandalf.png
Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5234690 10/09/19 09:20 AM
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CT8 Offline
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Give the oil a try. That will be the only way to see if the different oil changes the consumption.


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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5234727 10/09/19 09:55 AM
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buster Offline
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If the guy you bought it from previously used synthetic, the synthetic oil could be doing some cleaning and you're now seeing a spike in oil consumption. Synthetic oils have a lower volatility, generally speaking, than conventional oils.


2019 Frontier Pro 4X - RGT 5w30
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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5234794 10/09/19 10:54 AM
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Propflux01 Offline
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Most synthetics seem to be on the lighter side of the viscosity chart than mineral oils. But if your using that much, you have other issues.


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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5234822 10/09/19 11:39 AM
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The molecules in synthetic oil are nearly uniform is size. That's usually an advantage.
Mineral oil molecules vary in size.
In Europe, I would think you could find some Xw-60 oil for an older Harley.
You might also consider a straight weight oil like 40 or 50 if such an oil is available.
Sounds more like the rings are worn; not a rare thing for the H-D engines.

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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5234824 10/09/19 11:43 AM
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Blkstanger Offline
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Are your breathers working correctly? Puking oil? I'd bet you are not actually burning it.


99 Jeep WJ 4.7 200,000mi. Maxlife 10w30, Fram Ultra.
15 Ford Escape S 2.5
Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5234963 10/09/19 02:20 PM
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During each power stroke, the cylinder walls are subjected to very high temperatures, often 4000
degrees F or higher. This period is very brief but nevertheless, long enough to cause oxidation of
minute quantities of some of the lubricating oil on the cylinder walls. Some of this oxidation will
settle into the "valleys" of the honed cylinder wall "scratches." Eventually this situation will fill
the "valleys" of the cylinder walls creating a smooth, flat surface. This is also a normal situation;
however the ring break-in process practically ceases when these valleys become filled or "glazed"
over.

If this "glazed over process occurs before break-in is complete, in modern day language, "you
have had it." Excessive oil consumption resulting from incomplete ring seating will present itself
and the only certain remedy is rehoning the cylinder walls.

[Linked Image]


Larry L
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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5235069 10/09/19 04:27 PM
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Silverado12 Offline
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Those are easy enough to do a top end on anyways, even if you pay someone it's not too expensive.


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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5235330 10/09/19 09:58 PM
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My Hayabusa used Mobil 1 10W-40 full synthetic motorcyle oil, but never used any oil when I used Valvoline non-synthetic 10W-40 motorcycle oil, or other non-synthetic 10W-40 oils.

So it certainly can make a difference in the amount of oil the engine uses.

Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5236711 10/11/19 08:37 AM
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alarmguy Offline
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Originally Posted by Gummybear
Hi Guys,

my 1993 Harley Davidson sportster needs about 1 liter 20W50 Castrol Synthetic Oil every 625 miles ( 1000 km ). This is too much ( twice what could be considered as normal ). The person who sold to me this motorsicle says "it is because you use synthetic oil".
What do you think ? Will the use of mineral oil with the same viscosity 20W50 decrease the oil consumption ?
If yes, I would be pleased if someone could explain why ?

Thanks

Regards

Gummybear


Yes, conventional will decrease oil consumption, just keep in mind it depends on engine condition also.
Synthetic oil molecules are all the same size and a bit smaller, also depending on brand the viscosity MIGHT be a little thinner with synthetic within the same API.

Conventional oil molecules are a bunch of mixed up large and small molecules. I actually prefer conventional oils or semi syn, if your looking for less oil consumption go with 20w50 and based on the age of your engine, IF available I would choose 20w50 Valvoline Maxlife semi syn and if that didn't work a straight conventional or maybe not even play around and go straight conventional if it can be found.
Heck, even conventional Valvoline Motorcycle oil 20/50 would be good.

I dont think your doing your engine any good running a full syn if you change your oil when your supposed too. At the same time, I dont think your doing it any harm either.

Last edited by alarmguy; 10/11/19 08:39 AM.

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Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5236727 10/11/19 08:52 AM
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sunruh Offline
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1st you just can say that conventional will use less that synthetic. lots of variables

many places you could be losing it

rings, valve seals, breathers, gaskets, drain bolt....a crack that only opens under load


motorcycle oil myth buster
Re: are molecules of mineral oils thicker than those in synthetic oils ? [Re: Gummybear] #5237006 10/11/19 01:20 PM
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alarmguy Offline
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^^agree^^ But its a heck of a good cheap starting point while examining other possibilities of which some already may have been or may not.

Last edited by alarmguy; 10/11/19 01:21 PM.

14 Road King (current)
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