Can an oil be too thin at start-up?

[The Critic]

Yes, I understand that a thinner oil at cold temperatures will flow more rapidly, hence a possible reduction in start-up wear. However, will the reduced oil pressure be an issue? Isn't lubrication also dependent upon oil pressure?

TIA.

 

[Shannow]

Nope, pressure has very little to do with anything but hydrostatic lubrication.

No vehicles, and not very many machines use hydrostatic lubrication these days.

 

[Ugly3]

Not a chance!

 

[Oil Changer]

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Yes, I understand that a thinner oil at cold temperatures will flow more rapidly, hence a possible reduction in start-up wear. However, will the reduced oil pressure be an issue? Isn't lubrication also dependent upon oil pressure?

TIA.

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I love the 0WXX oils! One thing I love about them is the way my oil pressure rockets from zero at start-up to what I presume is bypass within miliseconds. I run 0WXX oils in all my vehicles year-round.

 

[Black Bart]

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Nope, pressure has very little to do with anything but hydrostatic lubrication.

No vehicles, and not very many machines use hydrostatic lubrication these days.

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While using a 0xxx will be fine your comment about not needing oil pressure is just flat wrong. Don't believe me drain the oil and see how far you get without oil pressure. How much do you need well old hotrodders alway shoot for 10lbs per thousand rpm so how much is required depends on how many RPM your engine turns.

 

[Drew99GT]

I think he was referring to oil flow vs. pressure. Sure, having no oil and the resultant no oil pressure will kill and engine. But the actual lubrication, ie. parts separation has little to do with the actual pressure forcing to components apart. Most parts of an engine short of the bottom end bearings don't even get full flow pressurized oil; they get splash lubrication.

 

[XS650]

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I think he was referring to oil flow vs. pressure. Sure, having no oil and the resultant no oil pressure will kill and engine. But the actual lubrication, ie. parts separation has little to do with the actual pressure forcing to components apart. Most parts of an engine short of the bottom end bearings don't even get full flow pressurized oil; they get splash lubrication.

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Bingo. If you look at where the oil is injected into journal bearings, you can see that the pump pressure is actually forcing the wearing surfaces together. It doesn't matter because pump pressure is absolutely insignificant compare to hydrodynamic pressure generated in the bearing itself.

 

[Greaser]

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Yes, I understand that a thinner oil at cold temperatures will flow more rapidly, hence a possible reduction in start-up wear. However, will the reduced oil pressure be an issue? Isn't lubrication also dependent upon oil pressure?
I second that!
TIA.

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I love the 0WXX oils! One thing I love about them is the way my oil pressure rockets from zero at start-up to what I presume is bypass within miliseconds. I run 0WXX oils in all my vehicles year-round.

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[Curious Kid]

I to have come around to believing that "no oil is thin enough at start-up," though I have no data collectted of my very own. I do wonder though for those that suffer piston slap, though IIRC that it doesn't appear to harm anything (correct me if I'm wrong). In such cases, I though a slightly thicker oil was often the solution to quiet things down.?.

Flow for cooling and replenishment of what was displaced within clearences.

 

[XS650]

Something that gets left out of these discussions is the fact that if oil were as thin at startup as it is at operating temperature, the bearings would be drier at startup than they are now because they would drain better overnight with the thin oil. It still takes a few engine revolutions to get oil moving

 

[Ray H]

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Most parts of an engine short of the bottom end bearings don't even get full flow pressurized oil; they get splash lubrication.

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Really... What in the engine splashes oil up to the camshaft and hydraulic valve lifters under sufficient pressure keep the cam lobes lubed and the hydraulic lifters sufficiently pressurized to avoid tappet clicking? Now, if you really meant to say secondary pressurized lubrication subsequent to fulfilling big-end lubrication, that would make sense to me.

 

[AEHaas]

No.

If an oil is as thin as it was when you turned off your engine, then it would get back up into the upper engine faster than if it thickened, as it normally does after engine shut down. In a journal bearing there is no loss of oil in any event as it is kept in the area by capillary action.

It takes up to several minutes to get oil to the top end when an engine is started.

Pressure has no effect on lubrication except to deliver oil to the site.

Oil is the most thin when you turn off your hot engine and certainly it almost all falls off the camshaft within minutes. It is therefore most important to get it back onto these areas with an oil less honey-like on start up.

Here is a chart provided by another member of oil thicknesses at various temperatures:
Kinematic Viscosity in cS.

T(C)M1 0W30* M1 5W30* M1 10W30* M1 0W20* RL 5W20
-20° 1994 2225 3424 1712 2995
-10° 872 944 1332 730 1165
0.0° 428 452 595 352 521
10° 231 240 298 188 261
20° 135 138 164 109 144
30° 84.6 85.5 97.6 68.3 86.3
40° 56.0 56.0 62.0 45.1 55.0
50° 38.8 38.5 41.6 31.3 37.0
60° 28.1 27.7 29.2 22.6 26.1
70° 21.0 20.6 21.4 17.0 19.2
80° 16.2 15.8 16.1 13.1 14.5
90° 12.8 12.4 12.5 10.4 11.3
100 10.3 10.0 10.0 8.4 9.1
cP @ 150°C
HTHS 3.0 3.1 3.2 2.6 3.3

Note that at even 50 degrees oil is way too thick for your engine, assuming it is designed to operate with a viscosity of 5 - 10 cS.

aehaas

 

[Patman]

I've often wondered if it was technically possible to build an oil that is a lot thinner than other oils when cold, such as having a viscosity of around 20-25 cst at 40c for example, but still have a viscosity of around 10-11 cst at 100c? I'm sure it would need some super exotic kind of base oil to do it, but if it were technically possible an oil like that (with the right add pack too) would allow almost no engine wear at all.

 

[pzev]

Does that data exist for PP 5w30 and 5w-20?

 

[1sttruck]

Assuming that hotter oil at startup results in less wear, do wear metals in UOAs trend by season and geography ?

Do vehicles in hot climates last longer than in other climates ?

Does an oil pan heater pretty much eliminate engine wear ?

 

[AEHaas]

Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up).

Graphs show that the wear rate is exactly oil/engine temperature dependent. It may be that people use thinner oils in cooler weather and this helps. Also, cars with short trips and multiple start ups have much greater wear than those driven at a steady 70 MPH for long distances. Trucking companies often discourage turning off the engines.

aehaas

 

[G-MAN]

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I've often wondered if it was technically possible to build an oil that is a lot thinner than other oils when cold, such as having a viscosity of around 20-25 cst at 40c for example, but still have a viscosity of around 10-11 cst at 100c? I'm sure it would need some super exotic kind of base oil to do it, but if it were technically possible an oil like that (with the right add pack too) would allow almost no engine wear at all.

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I'm sure Molakule could blend you a batch of such an oil. Problem is, a quart of it would cost as much as your Vette.

 

[Ramjet Roger]

An interesting confirmation of this is to look at UOAs for long highway OCIs vs. short-trip/city driving with warm vs. cold weather thrown in. In my case, with a 5.7L Hemi, I did a 5,500 mi OCI within 2 weeks of constant highway driving this past summer. The Fe wear was 16. By comparison, a 2,481 OCI over 2 months of winter driving with mixed highway/city driving resulted in an Fe 25. This is with M1 5W20.

Roger...

 

[427Z06]

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I've often wondered if it was technically possible to build an oil that is a lot thinner than other oils when cold, such as having a viscosity of around 20-25 cst at 40c for example, but still have a viscosity of around 10-11 cst at 100c? I'm sure it would need some super exotic kind of base oil to do it, but if it were technically possible an oil like that (with the right add pack too) would allow almost no engine wear at all.

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It may help lower wear, but the data I've seen indicates that 50% of the cold start wear is unavoidable. (Starting an engine that is at 40C throughout is still considered a cold start). Further, under the most desirable conditions (like steady state 60 mph on a flat highway at operating temps), there is still some wear, which will vary by component.

 

[KW]

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It takes up to several minutes to get oil to the top end when an engine is started.

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Several minutes?

Must be a typo.

I have to agree that a few seconds can feel like a long time.

Kevin