Motor Oil 101

I have been accruing information again, this time on understanding oil. I have 7 chapters so far. Let me begin with chapter 1:

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.



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 pricipals 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

302...........................3
212..........................10
104..........................100
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 you 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.

 

Please continue

I know it has been talked to death here but I need convincing why I should switch from Castrol 20/50 to a synthetic oil in my 75 308 gt4? My drag racing brother in law workered for Conoco for 20 years and swears that dino oil is still better.

Sincerely,

Rob
Thats oil I have to say!

 

I would be glad to know how dino oil outperforms synthetic. Please give me specific, scientific examples. No chemist I have talked to has ever thought that.

Drag racers have opposing views from track racers. Dragsters are heavily blown engines producing thousands of BHP. The internal combustion pressures are far above those of cars.

The big problem with those engines is blow-by dilution of the oil from the gasoline/nitro/whatever they use. The engine starts with a 60 or 90 weight oil but ends up with a 10 weight oil by the end of the 1/4 mile race.

The problem is dilution. There is no relation to other types of engines whatsoever. Those with limited knowledge would think that all engines are better off with thicker oil. This is wrong. Most engines are better off with thinner oil.

aehaas

 

Very informative, and very plainly written. Kudos.

I look forward to the remaining five or six chapters/lessons.

 

One other anomoly that occurs when an engine cools is the increase of clearances between internal parts. The oil cools and gets thicker, the engine cools and clearances get larger.

Not to argue but to make an observation. An engine that rattles on start up isn't encouraging.

 

I'm all ears and I look forward to subsequent chapters.
Thanks for the info.

Philip

 

Ali, the only negative that I have been told by some experienced techs to using 0W-30 oil is that the oil light tends to start flickering at idle. The techs tell me that it is no big deal because there is not a problem. It is just that the sensors get fooled by the thinner oil. Have you experienced this in your cars?

Dale

 

Ali -

Thanks for the informative post, keep them coming. One question: you mention 302 deg several times in the post, is there some significance to the extra 2 deg beyond just saying 300?

>>On the track that temperature is up to 302F<<

>>in mid-summer the oil temperature would probably get up to 302 F<<

Thanks,

Gary

 

ALi, I am one who has always been confused by oil can numbers. Back in high school we would buy oil by brand and weight blindly based on what we were subjected to in advertisements or saw local shade tree mechanics put in
their hot rods. Glad to hear from you again, looking forward to next chapter.

 

"It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication."

I would insert the phrase 'high gauge' in front of the word 'pressure' to distinguish the location where pressure is critical to keep moving parts separated.

 

The biggest misconception is that 0W-30 is thinner than 10W-30 or a straight 30 weight oil. As you guys read the next chapters it will be more clear. This is the most difficult concept and most misunderstood. They all give the same thickness, the same , the same. They give the same viscosity, the same.
If you change from a straight 30 to a 0W-30 your engine pressure gauge will read the same pressure exactly. There is no difference in viscosity.

The reason I use 302 F is because I am converting all the standard temperatures used in the industry from Celsius. We use 40 C (104 F), 100 C (212 F) and 150 C (302 F) but people have trouble with Celsius in the US. It adds to the confusion in my experience so I am using what I find people understand best. We do not test at 75 F at all. I extrapolate the numbers to a temperature that is common for starting up our cars in the morning.

The current way of my writing is based on what I have found works best so that people can get some sort of understanding of this most difficult if not impossible topic.
I have been massaging my approach over the years and this is my current best effort. Time will tell if anybody actually gets it right.

aehaas

 

Great stuff Ali. I'll wait for chapter 2.

 

Ali, thanks for the great post. I certainly appreciate the new understanding. I have a couple of questions to calrify this understanding:

1. Do 5w30 and 5w40 behave similarly at start up?

2. If a car gets driven everyday would there be risidual lubrication left between the moving parts at each start up overnight or you would expect oil to drip down overnight and make no difference if a car is driven everyday or once a month.

Thanks,

Matt

 

DJ made the following point:
One other anomaly that occurs when an engine cools is the increase of clearances between internal parts. The oil cools and gets thicker, the engine cools and clearances get larger.
Not to argue but to make an observation. An engine that rattles on start up isn't encouraging.

I answer this in chapter 8 but the short is that most engine noise on startup is due to the exhaust system. It goes from room temperature to thousands of degrees in a minute. Numerous parts are rattling.

However, there are metallic engine noises and those are from the starvation of lubrication secondary to the massive thickening of oil at room temperature and below. This is the time that the 90 percent of the wear and tear is occurring. The oil is too thick to flow properly and therefore cannot lubricate. Remember that flow = lubrication.

The oil that falls off of parts has no adverse effects to my knowledge regardless of the time between starts.

0W-20 oil is less thick than 0W-40 at startup. I will go into this later.

aehaas

 

Speaking of oil...
Who knows of a US supplier for AGIP synthetic oil? (Other than the dealer)

thx
luke

 

Agip may be purchased directly from the importer:

800-922-9243

PS- I use the term importer loosely. My 5 gal. can of Agip SXA gear lube for my wife's Murcielago was made in Pennsylvania. Many products are made here to the specification from the parent company elsewhere.

 

Thank you Ali! Once you are done, your work can be compiled and included in resources. Thank you again.

 

The article is great and looking forawrd to cahpter 2 & Subs!!

The comment "Increased clearances when cold" is however incorrect.

When two components say a crankshaft and a connecting rod (Assume both are constructed of steel for the sake of argument) are heated or cooled equally they both expand at the same rate; the hole in the rod will expand and the crankshaft will expand. Essentially the gap will stay the same. The gap is only affected if the metals are dissimilar or the heating is not equal across both components.

Mark

 

Great article. Learned a lot. Do you know where we can get the 355 oil (Shell) and the 360 oil (shell). Given their prices, any help would be saving dollars.
Art

 

All synthetics that are API / SAE SL rated are essentially the same if you pick the same viscosity rating. I use Mobil 1 because it is readily available and relatively inexpensive. You do not need Shell. I do like Shell Helix Ultra, it is simply not sold here.

Some people argue all day that one brand is better than another. They are the same if they are SL rated and of the same viscosity. These are the facts.

aehaas

 

Most excellent post...next oil change will be 0-30...look forward to the rest...

 

Forgive me for pouring troubled water over oil , but I would like to add to the discussion some scientific facts about 'Viscosity'.

The main one is that there is no SI unit for viscosity. This is because 'thickness' varies with not only temperature, but also shear rate and other factors. When discussing thickness or resistance to shear, fluid dynamicists use the term Rheology. This is not a single measure, but a set of measures used to describe the complex behaviour of a fluid over a range of conditions.

The Rheology of synthetic oils is generally more stable over time, because they are based on the base fluid, whereas mineral oils tend to rely on polymers to give the required rheology. These polymers break down with time, temperature, and the chemical changes that occur in the oil when cycling between hot and cold.

This is why drag racers see little benefit in synthetic oils...the degradation is mostly down to fuel thinning the oil.

So my recommendation is to use the manufacturer's recommended oil if it is synthetic. It will have hopefully been properly tested and proved to provide acceptable performance under the range of shear rates experienced in their engine, and it's degradation will be acceptable within the service interval specified.

 

Ali, Please take no offense, strictly in the interest of knowledge and I guess being the devils advocate I offer the following;

I was alluding to the distinctive rattle of internal engine noises in the first 15 seconds of engine start up, namely valve train and wrist pin rattle/piston slap. Granted, I have heard exhaust rattle also and it is not easily confused with the other noises. My exhaust does not rattle.

I will wait to see what chapter 8 brings then maybe it will be clearer to me.

DJ

 

I stand corrected. I was thinking the differences in clearances would occur between dissimilar metals and their different rates of expansion, namely aluminum alloy pistons in a cast iron bore or for that matter, an aluminum piston in an aluminum engine with steel sleeves.

In order to achieve the correct (optimum) clearance at full operating tempurature the aluminum component would have to start out at a smaller size (hence larger clearance) to compensate for the higher rate of expansion than that of the bore itself.

More like it?

 

There is no rocket science here. 5W-30W has a viscosity = to the 5w when it is cold and 30W when it is hot. The oil is enhanced to thicken as it heats up. The problem here is when the additives start breaking down. This starts to bring the oil down to its base rate which will be 5W. Thus a worn engine with thin oil will be a problem. So weight is weight either syn. or dino oil , take your choise.

By the way doc you need to get out and play more golf.