Start up protection differences - 10w, 15w, 20w?

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Originally Posted By: Clevy
[

This nonsense that a 0w-xx will pump faster at start up seems to get said often however because oil pumps are positive displacement it doesn't matter if you've got a 0w-20 or a straight 60 grade in the sump because the oil pump will push the same volume of oil either way.


How many times are we going to fight this one out? A viscous fluid is going to flow slower through a network than a less viscous fluid at equal pressures. You might have to go to 1000 psi on a very thick oil to get the same flow rate of a very thin one. It ain't going to happen. The relief simply opens at the pump to prevent a shaft twist off.

Get it out of your head. Or is something else here very thick?

I'm really disappointed in you guys. Especially the more learned members. C- grades all around.
 
Originally Posted By: turtlevette
Originally Posted By: Clevy
[

This nonsense that a 0w-xx will pump faster at start up seems to get said often however because oil pumps are positive displacement it doesn't matter if you've got a 0w-20 or a straight 60 grade in the sump because the oil pump will push the same volume of oil either way.


How many times are we going to fight this one out? A viscous fluid is going to flow slower through a network than a less viscous fluid at equal pressures. You might have to go to 1000 psi on a very thick oil to get the same flow rate of a very thin one. It ain't going to happen. The relief simply opens at the pump to prevent a shaft twist off.

Get it out of your head. Or is something else here very thick?

I'm really disappointed in you guys. Especially the more learned members. C- grades all around.





In the OP the question was posed assuming the ambient tep was above freezing.
I would say, most engines at this temperature, running popular multigrade oil (up 20w-50) would not go into by pass, unless revved to a high rpm very early during the warm up phase.

If the Bypass valve remains closed, a 20w-50 will circulate to most places of an engine, just as quickly as a 0w-30

So I guess, that is why many manufactures in most parts of the world specify such heavy weight oils for above freezing climates.
 
Last edited:
Originally Posted By: turtlevette
Originally Posted By: Clevy
[

This nonsense that a 0w-xx will pump faster at start up seems to get said often however because oil pumps are positive displacement it doesn't matter if you've got a 0w-20 or a straight 60 grade in the sump because the oil pump will push the same volume of oil either way.


How many times are we going to fight this one out? A viscous fluid is going to flow slower through a network than a less viscous fluid at equal pressures. You might have to go to 1000 psi on a very thick oil to get the same flow rate of a very thin one. It ain't going to happen. The relief simply opens at the pump to prevent a shaft twist off.

Get it out of your head. Or is something else here very thick?

I'm really disappointed in you guys. Especially the more learned members. C- grades all around.





You are right, though you've used an extremely exaggerated example to make your point
wink.gif
With the relief closed, the flow between the oils, be it a 0w-20 or 20w-50, will be basically the same but the pressure generated to achieve that flow will be different. You use an oil outside of its designed operating range, or you use it in an engine with a higher volume pump or a lower pressure relief and the volume through the PUMP will be the same, but the volume the engine sees will not be as a portion of it will be going out the relief.

Now of course Shannow has touched on the topic of bearings being "self pumping" relative to this; drawing in what they need but that's outside the scope of this discussion.

There are a list of qualifiers that need to be mentioned when this discussion takes place (which is surprisingly frequent) but they seldom make themselves present, I assume for the sake of keeping the discussion simple. But it could be argued that this simplicity does nobody any favours particularly the individual who posed the question in the first place as they then do not get a complete explanation.
 
Turtlevette
Within any remotely applicable viscosity, the galleries will be filled at exactly the same rate regardless of viscosity.

The relief doesn't come in until the galleries are full... The pump moves the same amount to that point...there's your c grade

When full, the engine uses what it does... It's not a hydraulic circuit that needs oil pumped through it like some here think it is. Oil pressure is the artefact of system supply exceeding engine demand, as the designers intended.
 
Originally Posted By: tig1
A positive displacement oil pump will pump various vis oils at the same rate(volume), but higher vis oils(30-40-50wt) require more energy to pump the oil than say a 0-20 will. Also the higher vis oils produce more heat, when pumped, than a lower vis oil.


Close tig1, very close.

The power requirement for the pump is density*flowrate*pressure/efficiency.

Assuming both lubes hit the relief point, the power consumption of the pump will be identical. Roadgoing engines it's less than a hp. All that energy goes into heating to oil, and it's the same amount regardless.

In a world where the viscosity is dropped until the relief valve is closed, as some on BITOG posit is necessary, the difference in power consumption is proportional to the difference in pressures, and is about the quantum of a single headlamp in power consumption (and heat).

The real heat is due to the viscosus shear that takes place in the bearings and cylinders...Spinning an engine without fuel or spark gets you nearly there in terms of temperature...that's where the power loss comes in with thicker oils, not the oil pump drive.
 
Originally Posted By: Shannow
Turtlevette
Within any remotely applicable viscosity, the galleries will be filled at exactly the same rate regardless of viscosity.

The relief doesn't come in until the galleries are full... The pump moves the same amount to that point...there's your c grade

When full, the engine uses what it does... It's not a hydraulic circuit that needs oil pumped through it like some here think it is. Oil pressure is the artefact of system supply exceeding engine demand, as the designers intended.


It's amazing how much people will dance to save face for a member they like.

Look. That is not what Clevy said. Of course air will push out at the same rate because air has the same viscosity.

Bearings will take what they need but other sections of the engine benefit from additional volume such as side leakage providing piston cooling. More is better at high loads. The engine definitely is a hydraulic circuit.

I keep seeing the statement that the oil pump will move the same amount of oil regardless of viscosity and that is wrong to the Nth degree. It's just basic fluid mechanics. And you should and do know better. There is a good ole boy system and you're providing a dance and song in support of that system. That also exists in the professional world and angers me. You could be my worst enemy, but if you're right, you're right and a true and ethical professional will acknowledge that. I look at what is being posted not who the poster is.
 
Turtlevette,
designers who are trying to control piston temperatures put in squirters...squirters deliver volume based on oil pressure.

Your statement is absurd. To increase the side leakage of the big end, by dropping viscosity you reduce the minimum oil film thickness and the very load carrying capacity of the bearing...
 
Originally Posted By: Shannow
Turtlevette,
designers who are trying to control piston temperatures put in squirters...squirters deliver volume based on oil pressure.

Your statement is absurd. To increase the side leakage of the big end, by dropping viscosity you reduce the minimum oil film thickness and the very load carrying capacity of the bearing...


Squirters will also flow more oil on less viscous oils. It's just a small orifice.

You always hang your hat on oil film thickness. If that is the only concern then run straight Lucas in your engine.
 
I recently started an engine that had been sitting for over a year.

On this particular engine, I was able to remove the distributor and with the aid of an electric drill, spin the oil pump until oil was up to pressure.
Effectively, Pre oiling the engine.

Now, when I first started to turn the pump, it was spinning very fast with virtually no resistance.
This continued for several seconds ( and had me quite concerned)

Then some resistance was felt, for a second or two before I could feel even greater resistance, and the oil pressure started to rise (on the OP gauge)

What i'm suggesting is, the Oil pump had LOST IT'S PRIME!

Would this be more likely to happen with the use of a low viscosity oil?

*Spinning the pump with a drill by the distributor shaft, would be the equivalent of the engine driving the pump, while running at about 2000 rpm.
If the pump were not primed, this would mean the engine would have had to run at this speed for 10 -15 seconds, with only residual oil on the bores or in the bearings.
 
Originally Posted By: expat
the Oil pump had LOST IT'S PRIME!



That's going to happen to some extent on any engine. Some filters have check valves (anti drain back) and some don't, but you have no check valve at the pump. The oil is going to leak past the pump gears and back into the sump. You could have repeated the prime an hour later then a day later and compared to your initial results.
 
Originally Posted By: OceanRuns
How different is cold start-up flow/protection in a 10w-30 versus a 15w-40, versus a 20w-50?

Assume we're starting above freezing (vast majority of the time). Does the 10w circulate faster such that it reduces wear on start-up over the other two?

For you in California there's no difference. Xw grades come into play with extreme temperatures. Above freezing there's no difference. Unless you put in your system oil that's out of its designed temperature range (like using 20w in -30*C ambient) all cold viscosity grade oils perform similarly. But there is a catch. Usually a 0w and 5w are formulated with better basestock. If they were formulated with same quality base oils 15 and 20w would be more stable and less share prone due to less VII needed for this grades. There is no reason to use 0w (and 5w) grade oils except that we are forced to use them by manufacturers since only this grades carry their approvals.
 
Just because an oil is being pumped, doesn't mean that the majority of it is going anywhere but back to the sump.

Right after the oil pump is a pressure relief valve, so if you hit maximum oil pressure at least some of the oil is going through the relief valve back to the sump. If the oil is thick enough, this could be a LOT of it.

The oil filter also will be bypassing oil if it's thick enough. this means high viscosity oil which is likely to keep debris in suspension will go unfiltered to the oil galleries.

I get an oil with 1 "w" viscosity grade lower than the coldest expected temperature (cranking viscosity).
 
Originally Posted By: expat
I recently started an engine that had been sitting for over a year.

On this particular engine, I was able to remove the distributor and with the aid of an electric drill, spin the oil pump until oil was up to pressure.
Effectively, Pre oiling the engine.

Now, when I first started to turn the pump, it was spinning very fast with virtually no resistance.
This continued for several seconds ( and had me quite concerned)

Then some resistance was felt, for a second or two before I could feel even greater resistance, and the oil pressure started to rise (on the OP gauge)

What i'm suggesting is, the Oil pump had LOST IT'S PRIME!

Would this be more likely to happen with the use of a low viscosity oil?

*Spinning the pump with a drill by the distributor shaft, would be the equivalent of the engine driving the pump, while running at about 2000 rpm.
If the pump were not primed, this would mean the engine would have had to run at this speed for 10 -15 seconds, with only residual oil on the bores or in the bearings.


I doubt this would have been avoided with a higher W-rating, as most oil will have drained out before the engine gets cold.

A lower W-rating might have reduced the time needed to prime the pump again though.
 
Originally Posted By: Jetronic
I get an oil with 1 "w" viscosity grade lower than the coldest expected temperature (cranking viscosity).


That's a great rule of thumb...they are allowed to slip a W grade in service and still be "in grade", so pre-empting that, particularly coming into colder months is a great idea.
 
Originally Posted By: turtlevette
How many times are we going to fight this one out?

I think the disconnect here is with how one defines "pump faster." Rate of flow from the pump before bypass (as in volume per unit time), rate of flow after bypass (as in volume per unit time), and time for flow to begin (time elapsed from engine start to pumping being observed, as per the Esso video) could all be described as "pump faster," but are clearly not the same things.
 
Originally Posted By: turtlevette
Originally Posted By: expat
the Oil pump had LOST IT'S PRIME!



That's going to happen to some extent on any engine. Some filters have check valves (anti drain back) and some don't, but you have no check valve at the pump. The oil is going to leak past the pump gears and back into the sump. You could have repeated the prime an hour later then a day later and compared to your initial results.



The engine has been started repeatedly since that first start. OP comes up normally within a second or two.

When the engine was first built, the oil pump was filled with Vaseline for this very reason. To prime the pump.
 
Hmmm... I'm no engineer, therefore I offer this anecdote (rather than a double-blind, peer-reviewed study). In my old 2001 GMC Savana, the oil pump appears to bypass at around 60-65 psig on the factory gauge. I say that because, regardless of speed or temperature, the gauge will rarely go higher than that.

When started cold, California cold that is, regardless of the oil viscosity rating, the gauge goes up to around 65 psig. It remains there when driving off. Therefore, I conclude that the pump is bypassing, since engine rpm is increasing, and oil pressure isn't. After it warms up, idle pressure is about 25 psig, increasing to 65 psig at cruising speeds.

This van specs 5w-30, and has a 4.3 V-6. I generally have used 5w-30 or 10w-30.

I tried 20w-50 once as an experiment to see if it would slow oil consumption. It didn't. However, at a cold start, the oil gauge would reach 65-70 psig, and remain there when driving off. My conclusion, of course, was that the pump was bypassing, since oil pressure didn't increase with rpm.

My final conclusion was this: the lighter oil didn't pump faster since we're talking about a positive displacement pump, but it did move faster through the system, because at the same pressure (pressure set by pump regulator bypass), a thicker fluid will flow more slowly through the same restriction.
 
Originally Posted By: Stelth
My final conclusion was this: the lighter oil didn't pump faster since we're talking about a positive displacement pump, but it did move faster through the system, because at the same pressure (pressure set by pump regulator bypass), a thicker fluid will flow more slowly through the same restriction.

I like that explanation. It has some good rigour to it without me trying to convert the math of flow into an unwieldly mass of words.
 
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