Better Hydrodynamics with Thicker Oil? (Long)

[pitzel]

quote:

---

Originally posted by haley10:

Pitzel is probably including the oil in the overall big picture and 10% is doable. He's probably a good investor overall.

---

My analysis included fuel alone. This is how I did the calculation:

1) Assumptions: $84/year (1st year fuel difference), 3% inflation on fuel cost and in the general economy, 10% discount rate.

2) 20th year cost = 84 * 1.03^20, 19th year cost = 84 * 1.03^19, 18th year cost = 84*1.03^18 ...., nth year cost = 84*1.03^n

(takes into account inflationary effect on fuel).

3) Net future (20th year) of year 1 fuel = 84*1.10^20, net future (20th year) of year 2 fuel = 84*1.03^2*1.10^19, net future (20th year) of year 3 fuel = 84*1.03^3*1.10^18, .. net future value of year n fuel = 84*1.03^(n-1)*1.10(20-n).

4) Sum of net future (20th year) values = Sum(n=1..20)[84*(1.03^n)*(1.10^(20-n))]

5) Convert to 2004 (Present) dollars by dividing by 1.03^20, the inflationary multiple:

Net Present Value = {Sum(n=1..20)[84*(1.03^n)*(1.10^(20-n))]}/1.03^20

When all that math is done, the result is equal to approximately $3600 of present 2004 dollars. Anyone want the Excel spreadsheet for the calculation?

[ December 31, 2004, 03:41 PM: Message edited by: pitzel ]

 

[427Z06]

quote:

---

Originally posted by pitzel:
Anyone want the Excel spreadsheet for the calculation?

---

No thanks. You already have me feeling guilty for drinking $8/6pk Anchor Steam instead of $3/6pk Budweiser swill.

 

[CelicaGT6]

quote:

---

Originally posted by pitzel:
Personally, I wouldn't obsess over engine wear, moreso, I'd be very concerned about wear on other parts of the car. Any dino 5W-30, 10W30, or synthetic will do just fine in that car with 7000 mile OCI's, and will easily last 200-300k miles if maintenance is reasonably diligently performed and correctly performed.

Thicker oil, more correctly, more viscous oil, will not necessarily reduce wear. A 5% loss in fuel efficiency from using the improper oil can make a huge dent on one's pocketbook and really make the whole scheme very uneconomical.

Consider this example: You drive 20,000 miles/year, and the Escort gets 30mpg with 15W50 and 32mpg with 10W30 or 5W30. 2mpg difference amounts to 667-625 = 42 gallons of fuel @ $2.00/gallon = $84/year.

Over 20 years, with an interest rate of 10%, and a rate of inflation of 3%, in present (2004) dollars, that is $3600, easily enough for a brand new engine and/or a used 10-year old Escort in decent shape 20 years from now. The extra $$$ you spend on pricey Mobil1 synthetic oil and excessive filter changes just make the whole idea of using 15W50 in a misguided attempt to extend engine life an even worse financial disaster. And I haven't even mentioned any of the risk factors in terms of taking advantage of your 'investment' in excessive expensive synthetic oil changes.

---

Though I appreciate the financial analysis, I am not particularly concerned with the money saved since that is all speculative anyway.

For all I know, the car could just fall apart at the 200,000 mile mark and my careful maintenance would be a waste.

If the engine normally lasts 200,000 miles and I get 400,000 miles out of the engine with this theoretical better maintenance then the loss in mileage is a moot point as the extra 200,000 miles would the same as swapping in a used low mileage motor without the work. Besides, if I only lose 1 mpg, your estimate is off by 1/2.

Plus, the fact that I am maintaining the vehicle means that the rest of the car won't be trashed. Finding a 20 year old Ford Escort 15 years from now for under $4000, in good shape, would be hard to find, and frankly not worth it.

There are too many variables to speculate whether my plans are fiscally conscious. Maybe the car will be driven less, maybe the price of gas will go down, etc.

Maybe I should have omitted the details on my own vehicles since I was actually just looking for technical details regarding the statements made by the other chap. My fault for not clarifying. I apologize.

 

[pitzel]

quote:

---

Originally posted by CelicaGT6:

Plus, the fact that I am maintaining the vehicle means that the rest of the car won't be trashed. Finding a 20 year old Ford Escort 15 years from now for under $4000, in good shape, would be hard to find, and frankly not worth it.

---

I should clarify the concept of '2004 dollars'. When considering the 'time value of money' in economic analysis, we use calculations of inflation to reference present-value dollars. In the example I provided above, the comparison I made above, you would be looking at a 2015 Escort in 2025, and that Escort would cost you roughly $5000, which is essentially $3600 of 2004/2005 dollars inflation-adjusted for the year 2015.

Go onto the market today and look at what a 1995 Escort would cost you with 150k miles. Can't be much more than $3600. Thats what I mean by 2004 dollars, and I wouldn't expect things to change much in the future. If anything, given recent trends, I would expect autos to become cheaper in the future due to increased production in China on account of lower labour costs.

 

[CelicaGT6]

quote:

---

Originally posted by Gene K:
I would not pay much attention to the pour points. They dont really matter. The oil pump will cease to pump oil long before that point.

The two numbers you want to pay attention to are the Cold Pump and Cold Crank Numbers.

5W-30 M1 will continue to pump far below the point at which 15W-50 ceases to.

Most engines have a preferred operating viscosity this will vary with engine design.

Once this is established oil temperature will be the major factor in deciding the SAE rating to use.

20 Weight @ 100&#176C is thicker than 70 Weight @ 150&#176C

Gene

---

Let's expand on this post since that is the direction I wanted to go with this thread.

quote:

---

The two numbers you want to pay attention to are the Cold Pump and Cold Crank Numbers.

---

How are these numbers represented and do engine manufacturers provide requirements?

Will these numbers matter at temperatures above O*C? Does thicker oil "stick" better to parts helping with cold starts? Does oil thickness vary much at normal cool starting temps like 40*F?

I've noticed oil manufacturers do not post information about normal cold start up temps. They should start posting engine oil information about 40*F or something normal like that. Very few people drive their vehicles in -45C temperatures so that information is almost for bragging rights exclusively though you can usually infer that it flows better at 0*C if it pours at -45*C. But what if two oils pour at -45*C which will flow better at 0*C?

To raise questions about my own original post:

Do oil leaks mean engine wear?
Do tests show that thicker oil retains its viscosity longer?
Is there validity to this statement:

quote:

---

Honestly, it's hard to say. I have driven the S4 in -6*F, which included a cold start - it was kind of hard to start that morning - something I could not attribute to oil because I don't know what condition my battery was in with that kind of temperature extreme. On edit - to clarify, it was a slow crank, and fired up right away.

Yes. It's a tradeoff, because engine oil works by forming a hydrodynamic wedge between surfaces to provide lubrication. You gain lubrication benefits, but lose horsepower through oil drag.

Oil doesn't do its job at startup because there is no hydrodynamic action on startup. Under these conditions oil is only protecting through film lubrication, because the oil molecules act like magnets and stick to ferrous metals and each other. To further explain how oil "works" in an engine:

Viscosity pulls the oil between the two components, such as a piston and a cylinder wall, journal and bearing, etc, and forms a pressurized "gap" of oil. This is totally and 100% completely different than "film lubrication". The pressure increases with viscosity and speed, providing better lubrication by preventing scrubbing contact (assuming your machinework is perfect).

---

Is there truth to this:

quote:

---

People give me **** all of the time because I play in the upper RPM band all of the time - what they fail to understand is that the lubrication is BETTER at higher RPM, and you'll see less wear over a longer period of time. Audi also uses a high idle strategy when cold to make sure there's sufficient pressure right away to start hydrodynamic action.

---

If the oil pump is pressure regulated and thicker oil generates higher pressure sooner, this would imply that with thicker oil, the oil flow is less even though the pressure is the same. Right? I am trying to remember the rules from my fluid dynamics courses, so I could be completely off base here.

 

[jbas]

As a CFA, I enjoy the financial analysis! But I would disagree with the basic premise that switching a Ford Escort from 15W-50 to a lesser grade would gain 2 full MPG. Maybe 0.2 MPG (I would believe that: isn't there a statistical MPG standard for "fuel efficient oil?). And I would have to believe that most of the mileage gain would have to occur at start-up, not when both oils are warmed-up.

Replacement cost would also have to be factored in if the Escort lasted 100,000 miles with a 5W-30, and IF the Escort lasted 125,000 miles with the 15W-50. Oh yeah, what if the cars were driven in Florida? Ouch...never mind, mind spinning.

Put me in the camp that protection of the engine exceeds any other concerns, including MPG. (And the more protective visc may actually be the 5W-30!)

 

[Geoff]

If an engine just died one morning that would be one thing. Its the blue smoke puking, low compression, emissions failing, knocking slow death that I am trying to avoid.

 

[MGBV8]

Is it Possible that oil on start up and when overcooled , the piston rings will "hydroplane" over the oil and, on the upward stroke, scraping it into the combustion chamber where it will be burned, leading to carbon deposits and an increased risk of preignition. Also would pump produce cavitation.

Possibilities of vis change, vis improvers breakdown (usually more with thicker oil and mineral), Oil burn off, soot, fuel dilution.

 

[MGBV8]

Also other engine faults are likely to damage engine such as fuel injector wear producing bore wash.

 

[n8wvi]

Has ANYONE documented lower fuel mileage associated w/ heavier weight oil? In my '97 Subaru, the thinnest oil I've run was Mobil1 5w-30, ran it for > 60,000 miles. The thickest I've run was Delvac 1300S 15w-40, ran it for around 6,000 miles. The mileage on the Delvac was not one bit lower than on the Mobil1. Same driver, same driving habits. Same mileage, even w/ an oil that was quite a bit thicker.

Dave

 

[Fuelrod]

Oils first job is lubrication. It's second job is cooling. Third is cleaning. If you choose an oil that is too thick, its flow rate through the bearing becomes too slow, and the viscosity drag is too high. Overall oil temperature will rise with the increased friction caused by the oil itself. The hydrodynamic cushion forms instantly in any pressurized plain bearing. If 30 weight oil forms a cushion that the engine operating parameters can not break down, then 30 weight is thick enough and switching to 40 or 50 results in NOTHING other than lost power and increased waste heat. An oil cooler lets you run thinner, not thicker, oil. 30 weight is "thicker" than 40 weight if it's running at 150 degrees and the 40 is running at 220 degrees....

Racing engines, which operate under bearing loads 3 or 4 times what a street engine will ever see, will have a much larger bearing clearance which can flow 50 weight oil at high volume. They get a new set of bearings every race....

[ January 09, 2005, 08:20 PM: Message edited by: Fuelrod ]

 

[Dr. T]

QUOTE]Perhaps Dr.T is a Euro-car driver and had a bad experience. Japanese and American vehicles do fine with these high quality thinner oils.[/QB][/QUOTE]

Although I do currently run a European car, knowing what I know now I always wondered why all engines (American and Euro) that I've previously owned turned a 5-30 black by 2-3k and consumed it even in brand new engines.

Secondly, although Japanese engines may spec. a 5-20 here, they don't in Japan. Same with Ford in Australia. Throw the engine clearances and higher oil temp. theories out the window....

 

[mechtech]

I'd like to know exactly which engines use 'oil drag' to actuate/control cam timing.

 

[moribundman]

quote:

---

If 30 weight oil forms a cushion that the engine operating parameters can not break down, then 30 weight is thick enough and switching to 40 or 50 results in NOTHING other than lost power and increased waste heat.

---

"the engine operating parameters" are not constant, though. You may well drive an engine in a manner that allows you to safely use for example a 0W-20 oil. That does not mean that oil will protect the same engine sufficiently under anyone else's driving conditions (driving style + climate).

Anecdotal evidence: redlining my 1989 Scirocco for more that 30 minutes resulted in critical oil pressure loss at a still acceptable oil temperature of about 125 degree C. I had this issue only with a xW-30 oil in the summer heat, but not with 5W-40 and up. Viscosities for that engine were (All temps refer to ambient temp):

Full synthetic friction-modified oil, VW500.00 (Remember, this is before VW502.00):

no viscosity listed, but for ALL temperatured (< -20 C --> > 30 C)


Multi grade oil, VW 505.01 (spec still exists)

20W-40, 20W-50, >/= -10 C
15W-40, 15W-50, >/= -15 C
10W-30, 10W-40, -20 C --> 15 C
5W-30, 5W-20, < -10 C


Mono grade oils give another clue:

SAE 40, > 20 C
SAE 30, 0 C --> 30 C
SAE 20, -10 C --> 10 C
SAE 10, < - 5 C