Why Do Knowledgeable Folks on Here use 20 wt Oil

[johnmyster]

Ah yes ... the graph I posted in a one of those dead horse beating threads on PD oil pump operations, lol.

Whatever the HP and fuel mileage savings claim is due to running a thinner oil, it comes from a combination of both less oil shearing and less oil pump input power to pump the oil through the system. Yes, the claim of 3% to 6% increase in fuel mileage (wherever that came from) is obtained by going down from xW-30 to xW-20 is way too high.


Yes, the hydraulic HP required is small. The HP equation above is for a 100% efficient pump ... your favorite "pump slip" stuff, lol. You have to divide by the pump efficiency to be totally accurate. But healthy automotive PD pumps are in the 80-85% efficiency range, so it wouldn't make much difference here. So, (7.5 x 45)/(1714 x 0.85) = 0.232 HP.

"Even if the pan is only 10% efficient" ... you mean pump I assume.


If you assume the oil pump was not in relief (to make this example simpler), and the pressure at 2000 RPM went down from 45 PSI to say 40 PSI due to a decrease in oil viscosity, then the delta in required pump input HP would be as show below. If the pump is in relief, then you'd have to know the actual flow vs pressure curve of the pump as the RPM increases while in relief as shown in the Melling pump graph.

(Q x P)/(1714 x E) = Pump HP
(7.5 x 45)/(1714 x 0.85) = 0.232 HP
(7.5 x 40)/(1714 x 0.85) = 0.206 HP

So it's only saving 0.026 HP, which is a 11.2% decrease from 0.232 HP.

An average car cruising down the road at 60 MPH needs approx 23 rear wheel HP (26 crank HP). That includes the HP to over come aerodynamic and rolling resistance.

So the actual realized delta pump HP savings on the system by going with a thinner oil is 0.026/26 = 0.1%. In other words wrt to the pump HP in this example, going with a thinner oil only saved 0.1% of the HP at the crank to move the car at 60 MPH.

The other crank HP savings would come from the reduced oil shearing, which this example doesn't account for. So maybe add another few tenths of a percent for the total savings. It's still a very small savings. Yeah, it doesn't pass the sniff test, or the calculation test.

I’ve never had a vehicle (atleast not one with a working oil pressure gauge) that cruised in bypass once remotely close to operating temp.

Given that we had a handy curve for a LS pump, I was envisioning my old GMT 800 half ton. It cruised 60 mph at probably 1700 rpm, 45 psi oil on 30wt hot, IIRC. But that 5300 pound truck wasn’t cruising at 23hp avg.

Pumping work for incompressible fluids is incredibly small.

 

[ZeeOSix]

I’ve never had a vehicle (atleast not one with a working oil pressure gauge) that cruised in bypass once remotely close to operating temp.

How do you know that? You'd have to accurately monitor both pressure and flow volume to know. Or at least have the pump curves for the pump in your engine. Nobody has a flow meter on their oiling system. What kind of oil pressure gauge did you have (ie: analog, digital) and how accurate was it? The digital oil pressure and oil temperature gauges in my Z06 were pretty accurate.

Given that we had a handy curve for a LS pump, I was envisioning my old GMT 800 half ton. It cruised 60 mph at probably 1700 rpm, 45 psi oil on 30wt hot, IIRC. But that 5300 pound truck wasn’t cruising at 23hp avg.

How much HP it takes to make a vehicle to cruise down the highway doesn't have any bearing on the HP the pump needs to move the oil through the oiling system, except depending on what gears you're in at 60 MPH ... if that's what might be implying (?). The LS6 in the Z06 was also at 45 PSI at ~1800 RPM with 5W-30 at 200F.

Pumping work for incompressible fluids is incredibly small.

Yes it is, as the hydraulic HP calculation shows.

 

[Plumb Bob]

Don't you know how magical 0W-20 oil is? It saves engines from the evil 40-grade!

My Hemi 5.7 just texted me...she wants that darn Delo out of the sump!

 

[johnmyster]

How do you know that? You'd have to accurately monitor both pressure and flow volume to know. Or at least have the pump curves for the pump in your engine. Nobody has a flow meter on their oiling system. What kind of oil pressure gauge did you have (ie: analog, digital) and how accurate was it? The digital oil pressure and oil temperature gauges in my Z06 were pretty accurate.


How much HP it takes to make a vehicle to cruise down the highway doesn't have any bearing on the HP the pump needs to move the oil through the oiling system, except depending on what gears you're in at 60 MPH ... if that's what might be implying (?). The LS6 in the Z06 was also at 45 PSI at ~1800 RPM with 5W-30 at 200F.


Yes it is, as the hydraulic HP calculation shows.

Alright mr agumentative.

1) I've had a few vehicles where the oil pressure could be read/watched via scanguage or similar. Dash guages being notoriously...misleading. I think for the exercise of estimating pump work, I was accurate enough to be in the ballpark. You get a good feel for it when cold bypass seems to happen at a logical/specification pressure. So, relevant. Are you saying that 40-45 PSI isn't logical/reasonable for a 5.3/6.0/6.6 at 1700-1900 RPM, hot 30/40 weight?

Oh, you're refuting that I knew when bypass was happening. Well when cold idle seems to hover at something like, I dunno, 62 or 68 psi with little response to RPM as you exit the neighborhood, and then later fall and become variable (with RPM) as the lube warms, that's a pretty good indicator of some mechanical bypass happening. And since we know pump slip doesn't just magically turn on (it varies with RPM, viscosity) then logic follows, pump bypass.

2) No, but the size of the vehicle in proportion to what it takes to drive the oil pump bounds the amount of fuel economy one might could expect by decreasing pumping work. So, relevant. Standing to gain 0.2 hp when it only takes 20 to cruise in your versa means alot more than gaining 0.2 hp when it takes maybe 38 to cruise in a suburbatank.

3) It was quite common in fluid dynamics exercises to see the dP term be the smaller, as opposed to the kinematic term for incompressible fluids. But this goes back to my initial point which you have yet to refute, although it seems you are trying to refute something. Some folks have quite the imagination as to how much effort is going into that little lube pump.

Whatever. You and I both agree the 3% is not feasible. I don't get why you want to make an argument of it, although I'm not surprised.

 

[TiGeo]

 

[ZeeOSix]

Alright mr agumentative.

It's called a technical debate ... some call it "technical bickering". Imagine that ... technical discussions on a (suppose to be) technical chat board.

1) I've had a few vehicles where the oil pressure could be read/watched via scanguage or similar. Dash guages being notoriously...misleading. I think for the exercise of estimating pump work, I was accurate enough to be in the ballpark. You get a good feel for it when cold bypass seems to happen at a logical/specification pressure. So, relevant. Are you saying that 40-45 PSI isn't logical/reasonable for a 5.3/6.0/6.6 at 1700-1900 RPM, hot 30/40 weight?

Never said your estimated pump work (HP) wasn't accurate, we got basically the same number but just commented that part of the pump HP equation should include pump efficiency.

Also, I told you what the LS6 oil pressure was, which was basically the same as your old GMT 800 half ton. How is that saying anything different than what you've said ... re: last sentence in your quote above. So far, on the same page.

Oh, you're refuting that I knew when bypass was happening. Well when cold idle seems to hover at something like, I dunno, 62 or 68 psi with little response to RPM as you exit the neighborhood, and then later fall and become variable (with RPM) as the lube warms, that's a pretty good indicator of some mechanical bypass happening. And since we know pump slip doesn't just magically turn on (it varies with RPM, viscosity) then logic follows, pump bypass.

I was talking about with hot oil, not cold. Sure it would be easier to determine that the pump was well into pressure relief with cold oil and some engine revs. But when the oil is fully hot, it's pretty hard to see were the pump is in relief. The oil pressure vs RPM at constant 200F 5W-30 on the LS6 was a real smooth curve, so no real indication where the pump was first in some level of relief.

2) No, but the size of the vehicle in proportion to what it takes to drive the oil pump bounds the amount of fuel economy one might could expect by decreasing pumping work. So, relevant. Standing to gain 0.2 hp when it only takes 20 to cruise in your versa means alot more than gaining 0.2 hp when it takes maybe 38 to cruise in a suburbatank.

Sure, but not what you tried to explain in the comment in the previous post - wasn't sure what the focus was (I even said so). If it took a tank 2000 HP to go 60 MPH, then even a 1 HP savings from pushing thinner oil through the engine would basically be invisible to the HP level it took to move the vehicle down the road.

3) It was quite common in fluid dynamics exercises to see the dP term be the smaller, as opposed to the kinematic term for incompressible fluids. But this goes back to my initial point which you have yet to refute, although it seems you are trying to refute something. Some folks have quite the imagination as to how much effort is going into that little lube pump.

If you don't know what I'm trying to "refute", then I certainly don't know. Exactly what do you think I'm trying to refute?

Yes, some people can't imagine the HP required, but I've been pointing out the hydraulic HP equation here for years.

 

[johnmyster]

It's called a technical debate.


Never said you're estimated pump work (HP) wasn't accurate, got basically the same number but just commented that part of the pump HP equation should include pump efficiency.

I used an efficiency of 10% because it is obviously far beyond reasonable and conservatively handicapped my result by driving power required to drive the pump up.

It's a frequent tactic in my trade. Make some obviously extremely conservative assumptions and when the final result still supports your conclusion, you have made a solid justification for the argument.

 

[ZeeOSix]

I used an efficiency of 10% because it is obviously far beyond reasonable and conservatively handicapped my result by driving power required to drive the pump up.

Exactly what does this 10% efficiency you used equate to? I did it my own way which was more straight forward. I know you don't believe that a healthy ( <--- key word) automotive PD oil pump is 80-85% efficient, but I told you in that other thread that the Melling pump shows it to be ~85% efficient. I'd say any good and healthy PD pump on an engine is in that same 80-85% efficiency range. And as said in the other thread, once the pump goes into any pressure relief, the pump efficiency doesn't matter because it's trying to push more volume than the pressure relief valve will allow.

It's a frequent tactic in my trade. Make some obviously extremely conservative assumptions and when the final result still supports your conclusion, you have made a solid justification for the argument.

I showed you exactly what my conclusion of this pump HP reduction with thinner oil was based on with the calculations. You think it's wrong? If so, you tell me why you think so.

 

[factorytuned2012]

it really bothers people on a forum over an oil viscosity that it can carry on for pages wow. The question is why knowledgable people use a xW-20. Why is other viscosities being mentioned? Lock it up

 

[ZeeOSix]

The question is why knowledgable people use a xW-20.

Because they don't understand Tribology, and just want to follow the CAFE driven OM.

It will get locked due to "technical bickering" instead.

 

[factorytuned2012]

Documentation and proof that fuel conserving oil causes engine damage leading to failure.

 

[ZeeOSix]

Documentation and proof that fuel conserving oil causes engine damage leading to failure.

Nobody said it automatically leads to engine failure. If someone used a really too thin oil and really pushes the engine hard it could lead to engine damage or even failure in an extreme case like that.

What people are saying, and what many controlled wear studies show (some very sophisticated measuring real time wear) is that thinner oil causes more wear because the film thickness between moving parts is reduced with thinner viscosity, especially if the thin oil is getting much hotter than normal driving temps, or overly diluted with fuel. At some point the viscosity will get too low to adequately protect the moving parts. It's basic Tribology.

 

[userfriendly]

it really bothers people on a forum over an oil viscosity that it can carry on for pages wow. The question is why knowledgable people use a xW-20. Why is other viscosities being mentioned? Lock it up

I know, it’s crazy when I can save the same amount of fuel by dimming the dash lights instead of running a thinner engine oil.

 

[Patman]

I know, it’s crazy when I can save the same amount of fuel by dimming the dash lights instead of running a thinner engine oil.

Or you can save even more and do both

 

[Kalle.J]

Or you can save even more and do both

Less oil in the sump too, weight savings! Think of the improved MPG's!

 

[Patman]

Less oil in the sump too, weight savings! Think of the improved MPG's!

I don’t quite go that far with my Civic but I do try to eke out the best MPG that I can. And as I have said many times, with the way I drive it, it definitely doesn’t need anything thicker than the 0w20 I always use. The engine is rarely above 2000 rpm and spends 90% of the time on the highway at the speed limit.

The Corvette on the other hand, lives a completely different lifestyle …

 

[Sequoiasoon]

I don’t quite go that far with my Civic but I do try to eke out the best MPG that I can. And as I have said many times, with the way I drive it, it definitely doesn’t need anything thicker than the 0w20 I always use. The engine is rarely above 2000 rpm and spends 90% of the time on the highway at the speed limit.

The Corvette on the other hand, lives a completely different lifestyle …

My Accord is a 6MT so sees the higher rpms in my daily drives. It had 0W-20 for many miles that I owned it as my others vehicles did also. They vary now between 5W-30 and 5W-40 of different brands.

Not sure how knowledgeable I consider myself but at some point some of them at least will be back on 0W-20. Why? Because $10 for a 5qt jug of M1 Hybrid helped 6 of them make it into my supply.

 

[Klutch9]

It’s crazy that this thread is still trending. Can we please lock it so everyone can save their energy for posting useful info somewhere else? Like starting another thick vs thin thread, perhaps…

 

[userfriendly]

It’s crazy that this thread is still trending. Can we please lock it so everyone can save their energy for posting useful info somewhere else? Like starting another thick vs thin thread, perhaps…

There must be something else you can look at on the internet.

What I’ve learned from this thread is friends don’t let friends use XW20.

Case closed. No tickee ,no laundry.

 

[Kalle.J]

It’s crazy that this thread is still trending. Can we please lock it so everyone can save their energy for posting useful info somewhere else? Like starting another thick vs thin thread, perhaps…

We already have a new one, cleverly disguised: Butter Softness
Soft vs Hard butter