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#4719728 - 04/07/18 05:22 PM Effect of Oil Viscosity on Oil Film Thickness
NICAT Offline


Registered: 04/05/18
Posts: 58
Loc: Azerbaijan
Hi Friends,
This is not another "Which is better, thin or thick oil?" thread. As there are tons of discussions about it in this forum smile
But i am a little confused, because Shell's research has different results compared with other researches. (Likely i have missed the point.)

Shell Research:
Quote:
The assumption that lower viscosity lubricants automatically give rise to thinner oil films in
key lubricated contacts in a gasoline engine is also open to question, particularly in the case
of piston rings. Laser Induced Fluorescence measurements have found that, in a Nissan
gasoline engine, the mid-stroke top ring oil film thickness was greater for an SAE-5W/20
lubricant than it was for an SAE-15W/40 lubricant. These effects were also observed in our
laboratory for monograde lubricants. Similar effects have been observed by S.L. Moore of
BP36. Figure 20 illustrates the observations. A qualitative explanation of such an effect
could be as follows : There are two routes by which lubricant reaches the top piston ring.
Route #1 (the “conventional” route) is that oil is left on the liner by the passage of the
preceding ring. The higher the oil viscosity, the larger will be the oil film thickness left on
the liner. Route #2 involves oil being transported to the top piston ring via the ring gaps
(such flows have been observed by Nakashima et al37), and this is thought to favour lower
viscosity lubricants. The precise balance between oil transported by the two routes will
determine whether the oil film thickness under the top ring is greater for a lower viscosity
oil or not.


However, another research shows that OFT is higher with 20w40 than 10w40
Quote:
Comparison of the performance of both SAE
10W40 and SAE 20W40, showed that the increase of
frictional power losses and oil film thickness in case of
SAE 20W40 was strongly related to its high viscosity
compared with SAE 10W40. The high viscosity of the
SAE 20W40 was substantially responsible for the
increase in shear stress in oil film, and could be a
strong reason for the increase in hydrodynamic friction
with the use of the SAE 20W40 oil.



Another research:
Quote:
The oils were compared with each other at different loads and speeds as depicted in
Figure 4.29 and Figure 4.30. Oils 026A, 001C, 004B and 001A which have similar
viscosity give similar OFT and oil AW004 which has the lowest viscosity of all oils
shows a smaller OFT, as expected. On the other hand, oil 097A has the highest OFT as
it has the highest viscosity.


Source:
https://priuschat.com/attachments/fuel-efficient-motor-oil-technical-article-pdf.11772/
https://www.researchgate.net/publication...bustion_engines
http://openaccess.city.ac.uk/11916/1/Oil%20Transport%20in%20Piston%20Ring%20Assemblies.pdf

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#4719807 - 04/07/18 06:34 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
Marco620 Offline


Registered: 02/25/14
Posts: 2220
Loc: Kansan,Heckler Koch fan
Interesting read. Thank you for posting.
_________________________
2015 Civic 170k mi.0w20 Redline/Archoil,HPS SRI,Yokohama/Borla Exhaust/Vibrant Resonators #1790/Tein Suspension
Go Nashville Predators!

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#4719831 - 04/07/18 07:02 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
MolaKule Offline


Registered: 06/05/02
Posts: 19135
Loc: Iowegia - USA
I agree with Shell.

This

Quote:
The high viscosity of the SAE 20W40 was substantially responsible for the increase in shear stress in oil film, and could be a strong reason for the increase in hydrodynamic friction with the use of the SAE 20W40 oil.


is discussing the fact that higher viscosity oils result in higher hydrodynamic friction and shear stress, a different topic. The thicker the oil, the more HP you're putting into the oil to shear it and the higher the oil temp.

OFT and MOFT are highly dependent on base oil types and additives. I can can have a low viscosity finished oil show good OFT and MOST by the selection of different base oil viscosities, base oil types, and vII's used.

As for the third article, what was the Delta OFT between the two oills?

Furthermore, I doubt all three studies used the same type of engine or test equipment, loads, etc.






Edited by MolaKule (04/07/18 07:08 PM)

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#4719851 - 04/07/18 07:20 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
Ducked Offline


Registered: 10/25/12
Posts: 4432
Loc: Taiwan
The Shell quote gives two of the mechanisms potentially involved in the piston ring situation, and suggests that thicker oil films can develop in that situation with thinner oil because it gets past the rings in greater volume, i.e. there is more flow.

As I read it, this is to some extent a special case, and does not conflict with the general positive relationship between viscosity and film thickness, where the supply of oil is not limited.

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#4719861 - 04/07/18 07:31 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
Linctex Offline


Registered: 12/31/16
Posts: 6186
Loc: Waco, TX
Originally Posted By: NICAT

Shell Research:
Quote:
Laser Induced Fluorescence measurements have found ....



I would like to know a little more of how this testing method functions.
_________________________
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

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#4719871 - 04/07/18 07:37 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
andyd Offline


Registered: 09/25/04
Posts: 7273
Loc: Marshfield , MA
Rings are not my primary concerns Bearings and cam lobes, then rings. hide
_________________________
'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2

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#4719917 - 04/07/18 08:13 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
Silk Offline


Registered: 07/26/03
Posts: 4614
Loc: New Zealand
I've replaced far, far more rings than bearings or camshafts because of wear....
_________________________
1987 BMW R65 - Penrite V Twin 20/50
2005 Nissan Expert - Gulf Western 10W-40
1996 Volvo T5 - Penrite HPR15 - 15W-60. Ryco syntec filter.

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#4719963 - 04/07/18 08:58 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: Silk]
ZeeOSix Offline


Registered: 07/22/10
Posts: 17911
Loc: PNW
Originally Posted By: Silk
I've replaced far, far more rings than bearings or camshafts because of wear....


I was just going to say that rings tend to wear out more than most other lubricated parts.

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#4720051 - 04/07/18 10:37 PM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: Silk]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2634
Loc: MN
Originally Posted By: Silk
I've replaced far, far more rings than bearings or camshafts because of wear....
Yer Lord of the Rings! Shot in NZ.

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#4720110 - 04/08/18 01:04 AM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: Ducked]
SR5 Online   content


Registered: 07/07/15
Posts: 4518
Loc: Down Under
Originally Posted By: Ducked
The Shell quote gives two of the mechanisms potentially involved in the piston ring situation, and suggests that thicker oil films can develop in that situation with thinner (lower viscosity) oil because it gets past the rings in greater volume, i.e. there is more flow.

As I read it, this is to some extent a special case, and does not conflict with the general positive relationship between viscosity and film thickness, where the supply of oil is not limited.


I think you nailed it Ducked. (Slight add to above for clarity)

Quote:
Route #2 involves oil being transported to the top piston ring via the ring gaps, and this is thought to favour lower viscosity lubricants.

This is one of the special cases where flow is one of the limiting effects. For general engine lubrication, in a moderate / warm temperatures, the constant displacement oil pump gives the same flow for all reasonable viscosities. So normally flow is not a limitation. Here the small gap in the rings allows more low viscosity oil through, and given that the ring space is not saturated and can take more, then this does help.

Very interesting point.
_________________________
Penrite Vantage 10W40 SN & A3/B4 + Wesfil-Cooper Z154

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#4720113 - 04/08/18 01:33 AM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: Linctex]
NICAT Offline


Registered: 04/05/18
Posts: 58
Loc: Azerbaijan
Originally Posted By: Linctex


I would like to know a little more of how this testing method functions.


https://www.dantecdynamics.com/measurement-principles-of-planar-lif

Originally Posted By: andyd
Rings are not my primary concerns Bearings and cam lobes, then rings. hide


My car has over 1.000.000 km on it, and both camshaft and crankshaft were in great condition during the rebuilt. Only replaced the rings.
Not sure about bearings, but they were not causing any symptoms smile Just replaced them also, since they were cheap.
Cheapest mineral oil was used the whole time.



Edited by NICAT (04/08/18 01:50 AM)

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#4720119 - 04/08/18 02:18 AM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
FordCapriDriver Offline


Registered: 10/22/15
Posts: 2450
Loc: Balearic Islands , Spain
Locally here in Spain a company called Cepsa ( major Spanish oil company ) makes a Mineral 20W-40 API SF/CF oil, it has quite high Zddp and is very cheap and i've been tempted to try it in the Capri for some time and see how it likes it compared to 20W-50 smile
_________________________
1975 Ford Capri II Ghia 3000 V6, - Shell Helix HX3 20W-50.
1988 Ford Escort MkIV 1.6 Xr3i Cabrio, - Comma X-Flow XS 10W-40.
1999 Peugeot 106 II 1.1 Max, On standby

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#4720120 - 04/08/18 02:21 AM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
SR5 Online   content


Registered: 07/07/15
Posts: 4518
Loc: Down Under
That's great 1 million KM on cheap mineral oil.

May I ask a few questions?
- what car / engine
- what oil viscosity (eg 15W40)
- what oil specification (eg API SL)
- what oil change interval (OCI)

Thanks in advance.
_________________________
Penrite Vantage 10W40 SN & A3/B4 + Wesfil-Cooper Z154

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#4720151 - 04/08/18 04:08 AM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: SR5]
Ducked Offline


Registered: 10/25/12
Posts: 4432
Loc: Taiwan
Originally Posted By: SR5
Originally Posted By: Ducked
The Shell quote gives two of the mechanisms potentially involved in the piston ring situation, and suggests that thicker oil films can develop in that situation with thinner (lower viscosity) oil because it gets past the rings in greater volume, i.e. there is more flow.

As I read it, this is to some extent a special case, and does not conflict with the general positive relationship between viscosity and film thickness, where the supply of oil is not limited.


I think you nailed it Ducked. (Slight add to above for clarity)

Quote:
Route #2 involves oil being transported to the top piston ring via the ring gaps, and this is thought to favour lower viscosity lubricants.

This is one of the special cases where flow is one of the limiting effects. For general engine lubrication, in a moderate / warm temperatures, the constant displacement oil pump gives the same flow for all reasonable viscosities. So normally flow is not a limitation. Here the small gap in the rings allows more low viscosity oil through, and given that the ring space is not saturated and can take more, then this does help.

Very interesting point.


Yeh, sorry. "Thinner oil" was definately ambiguous in that context.

Not happy about this.

Doesn't mesh with my "thicker is better" mantra and may contra-indicate my SAE40 / Delvac 15W40 blend.

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#4720154 - 04/08/18 04:13 AM Re: Effect of Oil Viscosity on Oil Film Thickness [Re: NICAT]
Shannow Online   content


Registered: 12/12/02
Posts: 40166
Loc: 'Stralia
But there's other Shell papers that show increased oil consumption with thicker oils, and the rings being less able to scrape them off.

Rings are the area where I've come across diametrically contradictory studies

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