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#635835 - 01/11/05 12:59 AM Motor Oil 101
AEHaas Offline

Registered: 01/09/05
Posts: 1335
Loc: Sarasota, Florida
Somebody suggested I stop by here. I will reproduce articles from

Chapter One - Motor Oil 101

I think it is time to go over passenger car automotive engine oils in detail. I will be writing several articles to be published soon so I will try to get some of it out here. I feel this is a very general topic for all car owners on this board.

This is a very difficult topic to comprehend. Everybody including good mechanics think they are experts in this field but few understand engine oils. Most of what I hear is the opposite of the truth. It is however easy to see how people get mixed up as there is always some truth to the misconception.

Please forgive me if I am too wordy or even verbose at times. I will be redundant for certain. This will be in areas that people have to hear things over and over again to get it right. Some will never be able to understand these concepts unfortunately. I base my thoughts on those whom I have been listening to in various automotive chat rooms and discussion with mechanics. I will try to minimize technical terms and be somewhat vague rather than exact. I will round and average numbers to make the point simple rather than mathematically exact. Thickness has the same meaning as viscosity. Viscosity is a measure of the resistance of a fluid (liquid or gas) to flow. Fluids with high viscosity, such as molasses, flow more slowly than those with low viscosity, such as water. Again, I am trying to explain general principals as I know them.

The greatest confusion is because of the way motor oils are labeled. It is an old system and is confusing to many people. I know the person is confused when they say that a 0W-30 oil is too thin for their engine because the old manual says to use 10W-30. This is wrong.

More confusion occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the problem with motor oil. It would be more correct to think that oil thickens when it cools to room temperature and THIS is the problem. In fact this is the problem. It is said that 90 percent of engine wear occurs at startup. If we are interested in engine longevity then we should concentrate our attention at reducing engine wear at startup.

Oils are chosen by the manufacturer to give the right thickness at the normal operating temperature of the engine. I will say this average oil temperature is 212 F, the boiling point of water. On the track that temperature is up to 302F. It is important to realize that these are two different operating environments and require different oils.

I will discuss driving around town first. Everything I say will be based on these conditions. At a later time I will discuss track conditions. Everything I say will be as accurate as possible without looking everything up and footnoting. I am trying to be general not ultra specific.

One thing that is no longer important is the ambient temperature. Older automotive owner manuals often recommended one oil for the summer and another for the winter. This is still necessary for air cooled engines but is no longer a consideration in pressurized water cooled engines. These engine blocks are kept at around 212 F all year round. The oil is around the same temperature as well. This allows for a single weight oil all year round. Again, this is not the same as on the track where the coolant temperature is slightly higher and the oil temperature is much higher.

Please forget those numbers on the oil can. They really should be letters as AW-M, BW-N or CW-P. The fact that we are dealing with a system of numbers on the can makes people think that they represent the viscosity of the oil inside the can. The problem is that the viscosity of oil varies with its temperature. A “30” weight oil has a viscosity of 3 at 302 F ( 150 C ) and thickens to 10 at 212 F ( 100 C ). It further thickens to a viscosity of 100 at 104 F ( 40 C ) and is too thick to measure at the freezing point of 32 F ( 0 C ).

30 weight oil:

Temperature ( F )....Thickness

32..........................250 (rough estimate)

The automotive designers usually call for their engines to run at 212 F oil and water temperature with an oil thickness of 10. This is the viscosity of the oil, not the weight as labeled on the oil can. I want to stay away from those numbers as they are confusing. We are talking about oil thickness, not oil can labeling. This will be discussed later. Forget the numbers on that oil can for now. We are only discussing the thickness of the oil that the engine requires during normal operating conditions.

The engine is designed to run at 212 F at all external temperatures from Alaska to Florida. You can get in your car in Florida in September and drive zig-zag to Alaska arriving in November. The best thing for your engine would be that it was never turned off, you simply kept driving day and night. The oil thickness would be uniform, it would always be 10. In a perfect world the oil thickness would be 10 at all times and all temperatures.

If the thickness of oil was 10 when you got in your car in the morning and 10 while driving it would be perfect. You would not have to warm up your engine. You could just get in the car and step on the gas. There would be little wear and tear on you engine, almost none. Unfortunately the world is not perfect.

The night before when you drove home from work the car was up the the correct operating temperature and the oil was the correct thickness, 10. Over night the engine cooled to room temperature and the oil thickened. It is 75 F in the morning now (I do live in Florida). The oil thickness is now around 150. It is too thick to lubricate an engine designed to run with an oil having a thickness of 10.

It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication. If pressure was the thing that somehow lubricated your engine then we would all be using 90 weight oil. Lubrication is used to separate moving parts, to keep them from touching. There is a one to one relationship between flow and separation. If you double the flow you will double the separation pressure in a bearing. The pressure at the bearing entrance is irrelevant.

In fact the relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related. Conversely if you choose a thinner oil then the pressure will go down. This can only occur if the flow has increased.

It seems then that we should all be using the thinnest oil money can buy. This is partly true. Let me use my 575 Ferrari Maranello as an example. I drive this car around town. The manual of this car states the target pressure is 75 PSI at 6,000 RPM. The gold standard is that all engines should have a pressure of 10 PSI for every 1,000 RPM of operation, not more, not less. After all, you do need some pressure to move that oil along, but only enough pressure, not more. More pressure is not better, it can only result from the impedance of oil flow. Remember that oil flow is the only thing that does the lubricating.

Note that Ferrari is not saying what thickness of oil to use. That can only be determined by experimentation. My engine oil temperature is running around 185 F as I drive around town on a hot Florida summer day. I have found that the thinnest oil I can buy that is API / SAE certified is Mobil 1’s thinnest oil. Even with this oil I get 80 PSI at 2,000 RPM. It is too thick for my application yet it is the thinnest oil money can buy. If I was on a hot Florida track in mid-summer the oil temperature would probably get up to 302 F. I will guess that the pressure would only be 40 PSI at 6,000 RPM. The oil I am using would not meet the requirement of 75 PSI at 6,000 RPM from Ferrari. I would have to choose a thicker oil for this racing situation. The oil I use now would be too thin at that very high temperature. (This is only partly true. Higher RPM running engines use thinner and thinner oils to get more and more flow. I will discuss this later).

High flow does more than lubricate. It is one of the things used to cool the hottest parts of your engine, the pistons, valve areas and bearings. This cooling effect is as important as lubrication in your engine. If your engine is running hot use a thinner oil. The flow will increase and so will the cooling. This is even more important in the racing condition.

Let us go back to the Ferrari manual. My older 550 Maranello only specified 5W-40 Shell Helix Ultra as the oil to use in all conditions. This car was designed for racing. As it turns out Ferrari now recognizes that not every owner races their cars. The newer 575 manual now states to use 0W-40 for around town situations even though Shell does not make this oil in the Helix Ultra formulation at this writing. They also recommend the 5W-40 by Shell if you insist on the Shell product. It is also the recommended oil for most racing conditions.

Ferrari recommends Helix Ultra Racing 10W-60 “for hot climate conditions racing type driving on tracks”. Note that they now realize the difference between the daily urban driver like me and the very different racing situation. These are widely different circumstances. I want to emphasize that they only want you to use this oil while racing in “hot climate conditions”. If you are racing in Watkins Glen up north use the 5W-40. If you are racing in Sebring in the middle of the Florida summer use the 10W-60. Around town in any climate, use the 0W-40.

It is time to dispel the notion that 0W-30 oil is too thin when our manual calls for 10W-30. A 0W-30 is always the better choice, always. The 0W-30 is not thinner. It is the same thickness as the 10W-30 at operating temperatures. The difference is when you turn your engine off for the night. Both oils thicken over the evening and night. They both had a thickness, a viscosity of 10 when you got home and turned your engine off. That was the perfect thickness for engine operation.

As cooling occurs and you wake up ready to go back to work the next day the oils have gotten too thick for your engine to lubricate properly. It is 75 F outside this morning. One oil thickened to a viscosity of say 90. The other thickened to a viscosity of 40. Both are too thick in the morning at startup. But 40 is better than 90. Your engine wants the oil to have a thickness of 10 to work properly. You are better off starting with the viscosity of 40 than the honey - like oil with a viscosity of 90.

I repeat: More confusion occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the problem with motor oil. It would be more correct to think that oil thickens when it cools to room temperature and THIS is the problem. In fact this is the problem.

This is the end of lesson number one.


About the author:
Dr. Haas is a physician and surgeon. He graduated from the University of Florida with a degree in biochemistry with honors. He studied motor oils since high school where he did independent studies on this topic. He studied the properties of viscosity.

When he was a general surgery resident in Chapel Hill he studied the flow mechanics of human blood. Today he continues his research by discussion of oil products with chemists in the field and chemists from the oil manufacturers.

He has personal racing experience in Formula Super Vee. He is his own Lamborghini and Ferrari as well as Mercedes mechanic.

#635836 - 01/11/05 01:15 AM Re: Motor Oil 101
High Plains Drifter Offline

Registered: 10/06/04
Posts: 108
Loc: Texas
I guess my question is, if what you say is true(and I'm not saying it is'nt) why are'nt motor oils built as "10's" and stay that way all the time? Cold or hot?

#635837 - 01/11/05 01:20 AM Re: Motor Oil 101
Dominic Offline

Registered: 07/04/02
Posts: 1853
Loc: Gilbertsville, PA
And alas I agree as will 99% of this board - but the problem continues when you factor in the following:

1. Economics... In order to get a good 0W-30 oil, you must buy synthetic and only synthetic. If you run synthetic, will your car last any longer than if you don't and choose a cheaper 5W-30 that costs 1/2 the price?

2. Shearing... Many oils tend to shear quite a bit when hot, and it appears the 0W-30s and 5W-30s shear more over 3,000 or 10,000 miles than 10W-30s. If you live in FL, where the engine oil never goes below 75F, why risk shearing under the long haul when the oil is up to temperature?

If these statements you present above are true, then why do I get lower wear numbers running a 10W-40 in my OHV iron block V6 than the recommended 10W-30... in florida [Smile] ?

I like what you said, but you are making the assumption that an "XW-30" will always be "10" when up to temperature, and this is not always true. However, making that assumption, and assuming THE MAJORITY of wear occurs at startup, then you are mostly correct [Smile] .

I know you know this and just didnt add it into your article... but its more than just the oil warming/cooling we should we concerned with. The other engineering aspect is the overall expansion and contraction of the engine... namely the pistons in the cyls, main bearings, cam bearings, etc. When they are cool they are contracted more and are therefore more "open" and need a thicker oil than "10" to keep them working properly. Definitely this occurs even with a 0W-30 low viscosity start-up oil, however it's just something to keep in mind too [Smile] .

Thanks for your article - stick around on the board! [Coffee]

#635838 - 01/11/05 01:38 AM Re: Motor Oil 101
AEHaas Offline

Registered: 01/09/05
Posts: 1335
Loc: Sarasota, Florida
Water has a viscosity of about 1 - 2 from freezing to boiling. It varies little. If we could find a substance that had a viscosity of 10 all the time that was not corrosive nor degraded then the whole field of engine oil science would end.


PS There are many more chapters to go.

#635839 - 01/11/05 06:10 AM Re: Motor Oil 101
AEHaas Offline

Registered: 01/09/05
Posts: 1335
Loc: Sarasota, Florida
Dominic, let me answer some of your questions.

Regarding the use of 0W-30 synthetic vs. 5W-30 dino oil:
I drive 20 min to work and usually less when going out to dinner. The car takes 20 min. to get up to full temperature (oil = 190 F). As you will see later the first 15-20 min. is where most of the wear occurs before the oil gets up to temperature. The major thing people are studying is how to minimize the thickening of oil after you turn off your engine. The major improvement of synthetic oil is that it thickens less after engine shutdown.

Modern name brand oils do not breakdown from shearing. In fact the major problem with oil today is the thickening that occurs with time and use. Both are important. Oils may thin 10 percent then thicken 60 percent over time. This is true also for synthetic oils but more of a problem with dino oils.

As you will see, for whatever reason, fuel dilution of thicker oils is much more of a problem then with thinner oils. These often have no problem with thinning from fuel dilution whereas 40 and 50 wt. oils may easily thin a grade or two.

Lastly, many engines are aluminum and the bore and pistons expand and shrink at the same rate so that clearances are basically constant, hot and cold.

When you say that the 30 wt. oil gives more wear than the 40 wt. oil - what oil brands, viscosities and rating - SH, SL or other, are you using? How many miles are on your engine and what is the oil pressure at 2, 4, and 6,000 RPM?

Modern 20 wt. oils often outperform 40 wt oils in many tests just because of modern additives.


#635840 - 01/11/05 07:05 AM Re: Motor Oil 101
Dominic Offline

Registered: 07/04/02
Posts: 1853
Loc: Gilbertsville, PA
Valvoline Maxlife 10W-30 vs 10W-40 SL grade. Oil pressure at 2k is 70psi, 4k is around 75psi, and 6k is nearly 85psi. The only difference I can tell between a 30 and 40 is at idle where my oil psi is 55-60 running 30, and 60-65 running 40. Otherwise, pressure looks the same under load and various RPMs. I have rughly 28,000mi on the engine and will be doing a UOA soon on the newer 10W-40 to verify whether it's a consistant drop in wear metals or not. I've been doing 3,000mi OCIs as well but plan to go synthetic and run 5,000 or more miles on changes in the future.

Thanks for your clarification too, and yes I do believe that the biggest problem is getting the oils thin enough for startup. And it does appear that a 0W-30 would come into grade sooner than a 10W-30, which would reduce wear... if they both heat up at the same rate.

#635841 - 01/11/05 07:20 AM Re: Motor Oil 101
AEHaas Offline

Registered: 01/09/05
Posts: 1335
Loc: Sarasota, Florida
A) If your pressures are true they are way too high. Also, see my oil data here running 0W-20 in my Maranello 575 :

B) A 20 wt. oil would be more appropriate if your figures were all at normal operating temperature.

Both are in my opinion.


[ January 11, 2005, 11:28 PM: Message edited by: AEHaas ]

#635842 - 01/11/05 08:33 AM Re: Motor Oil 101

Registered: 01/18/03
Posts: 186
Loc: An Alberta Garage
Good foundation for the layman but written in a style way too wordy.

#635843 - 01/11/05 04:19 PM Re: Motor Oil 101
AEHaas Offline

Registered: 01/09/05
Posts: 1335
Loc: Sarasota, Florida
I promised a priori not to be laconic.


#635844 - 01/11/05 05:39 PM Re: Motor Oil 101
MGBV8 Offline

Registered: 08/20/03
Posts: 283
Loc: uk
Would be interesting to compare HTHS rather than pressure for evaluating which viscosity. In the UK (not a warm climate) Shell and Castrol both offer the 10W60 oil, but its likely to be part Group III, wheras M1 offer 15W50 motorsport oil, but an ester based oil Motul 300V 5W40. Is this an indication of base oil quality when put under higher temperatures. Motul do offer a xX60 but is classed as a 24 endurance race product to handle fuel dilution.

For road use the M1 0W40 is one of the most highly specified oil re MB etc, wheras the implications would be the 0W30 would have been the better choice.

However for a road and track a 0W oil may not be able to provide the high temperature protection.

#635845 - 01/12/05 01:45 AM Re: Motor Oil 101
AEHaas Offline

Registered: 01/09/05
Posts: 1335
Loc: Sarasota, Florida
As you will see in the next chapters, the first number of the grade is not the "weight " of the oil.

How do I post a JPEG of oil data? Is there a way to upload info to this site?


#635846 - 01/13/05 12:29 AM Re: Motor Oil 101
Dominic Offline

Registered: 07/04/02
Posts: 1853
Loc: Gilbertsville, PA
naa actually its a GM engine, the popular 3800-II, and is spec'd to run that high. Thanks though [Smile]

#635847 - 01/13/05 01:44 AM Re: Motor Oil 101
Schmoe Offline

Registered: 05/12/03
Posts: 7279
Loc: Oklahoma
This also adds to my belief that you got to let the engine warm up before taking off. Regardless of ambient temperature, time is the factor.

#635848 - 01/14/05 07:31 AM Re: Motor Oil 101
pitzel Offline

Registered: 09/13/04
Posts: 1478
Loc: Saskatchewan, Canada
Originally posted by Schmoe:
This also adds to my belief that you got to let the engine warm up before taking off. Regardless of ambient temperature, time is the factor.

My personal belief around engine-warmup, especially in our extreme cold temperatures, is that a bit of load actually can be beneficial to the warm-up process, accelerate the warm-up process, and impart less per unit wear on the engine overall.

For example, if it takes 20 minutes of idling at 1000rpm to completely warm up an engine versus 10 minutes of driving at 1600rpm, would you not in fact come out ahead in terms of engine wear since the engine is subjected to effects of the colder oil for less time? Is there a significant difference in per unit revolution wear in an engine as it is warming up, ie: a certain absolute per unit wear rate at warmup revs, and a higher per unit wear rate at higher rpms?

I do have a problem with this statement:

Motor oil becomes permanently thicker with exposure to northerly winter type weather. This is more of a problem to mineral based oils. Waxes form. This is why it is a bad idea to even store a bottle of oil in a cold garage. It goes bad on the garage self just because it is exposed to the cold.
This is the first I have ever heard of this happening. The author makes this insinuation in other parts of the article as well. Also, I'm less than impressed with the insinuation that 7500 mile drains might be innappropriate, despite being recommended in manuals. BITOG members have repeatedely shown this is false.

You do not need to use the exact oil type and brand that your car manual tells you to use. Oils are pretty general.
Some VW TDI owners would certainly disagree [Razz]

Other than that, I more or less agree with much of the article and must say that the straight talk about pressure is a welcome change from all the myths of the relationship between oil pressure and lubrication.

[ January 14, 2005, 11:44 PM: Message edited by: pitzel ]

#635849 - 01/15/05 06:49 PM Re: Motor Oil 101
KW Offline

Registered: 09/04/03
Posts: 1686
Loc: Central Arkansas
I like the article, well written and informative.

Thanks for the good read!

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