<TABLE class=tborder cellSpacing=1 cellPadding=6 width="100%" align=center border=0><TBODY><TR><TD class=tcat>Motor Oil Basics</TD></TR><TR><TD class=alt1>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 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
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 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.
aehaas
Motor Oil 102
Chapter two. It gets more difficult.
We left off discussing that a 0W-30 weight oil is not thinner than a 10W-30 oil. They both have the same thickness at operating temperature. The 0W-30 simply does not get as thick on cooling as the 10W-30. Both are still way to thick to lubricate an engine at startup.
I have heard several people say that Porsche specifically prohibits a 0W-XX engine oil, that it is too thin. Now here is the partial truth I spoke of earlier. We will discuss multigrade oils. Earlier we said that a straight 30 weight oil has a thickness of 10 at the normal operating temperature of your engine. The multigrade oils 0W-30 and 10W-30 also have a thickness of 10 at 212 F.
The difference is at 75 F, your startup temperature in the morning.
Oil type... Thickness at 75 F...Thickness at 212 F
Straight 30...... 250......................10
10W-30............100......................10
0W-30..............40 ......................10
Straight 10........30....................... 6
Now you can see that the difference between the desired thickness your engine requires ( = 10 ) is closest to the 0W-30 oil at startup. It is still too thick for normal operation. But it does not have far to go before it warms up and thins to the correct viscosity. Remember that most engine wear occurs at startup when the oil is too thick to lubricate properly. It cannot flow and therefore cannot lubricate. Most of the thick oil at startup actually goes through the bypass valve back to the engine oil sump and not into your engine oil ways. This is especially true when you really step on that gas pedal. You really need more lubrication and you actually get less.
Note that a straight 10 weight oil is also too thick for your engine at startup. It has a thickness of 30. Yet at operating temperatures it is too thin having a thickness of 6. It needs to be around 10. The oil companies have added viscosity index improvers or VI to oils to solve this dilemma. They take a mineral based oil and add VI improvers so that it does not thin as as much when it gets hotter. Now instead of only having a thickness of 6 when hot it has a thickness of 10, just as we need.
The penalty is the startup thickness also goes up to 100. This is better than being up at 250 as a straight 30 weight oil though. Oil with a startup thickness of 100 that becomes the appropriate thickness of 10 when fully warmed up is called a 10W-30 weight motor oil. This is NOT as thick as a straight 30 weight oil at startup and it is NOT as thin as a straight 10 weight oil at full operating temperature.
The downside of a mineral based multigrade oil is that this VI additive wears out over time and you end up with the original straight 10 weight oil. It will go back to being too thin when hot. It will have a thickness of 6 instead of 10. This may be why Porsche (according to some people) does not want a 0W-30 but rather a 10W-30. If the VI wears out the 0W-30 will ultimately be thinner, a straight 0 weight oil. When the VI is used up in the 10W-30 oil it too is thinner. It goes back to a straight 10 weight oil. They are both still too thick at startup, both of them. The straight 0 weight oil, a 5 weight oil and a 10 weight oil are all too thick at startup.
This is just theory however. With normal oil change intervals the VI improver will not wear out and so the problem does not really exist. In fact, oils do thin a little with use. This is partly from dilution with blow by gasoline and partly from VI improvers being used up. What is more interesting is that with further use motor oils actually thicken and this is much worse than the minimal thinning that may have occurred earlier.
Synthetic oils are a whole different story. There is no VI improver added so there is nothing to wear out. The actual oil molecules never wear out. You could almost use the same oil forever. The problem is that there are other additives and they do get used up. I suppose if there was a good way to keep oil clean you could just add a can of additives every 6 months and just change the filter, never changing the oil.
When the additives wear out in a synthetic oil it still has the same viscosity. It will not thin as a mineral oil. The fear that some say Porsche has that oils thin when the VI runs out is not applicable to these synthetic oils. These oils will always have the correct thickness when hot and will still be too thick at startup as with all oils of all types, regardless of the API / SAE viscosity rating.
Automotive engine manufacturers know these principals of motor oils. They know there is thinning or thickening that will occur. They take these things into account when they write that owners manual. Mineral oil change recommendations will generally include shorter time intervals than those of synthetic oils.
The reality is that motor oils do not need to be changed because they thin with use. It is the eventual thickening that limits the time you may keep oil in your engine. The limit is both time itself (with no motor use) and/or mileage use.
End of part two.
aehaas
Motor Oil 103
Part Three. You have a synthetic mind.
Let us compare mineral and synthetic oils. I will not talk about chemical but rather functional differences. We discussed before how mineral oils are too thick at startup yet too thin when hot. The viscosity was corrected with the hot engine by adding VI improvers.
A 10W-30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 weight oil when hot. It acts more as a 10 weight oil at startup. I remind you that a 10 or 5 or 2 weight oil is still too thick to provide lubrication at startup. They are all too thick at startup. There is currently no engine oil thin enough to operate correctly at startup. They all cause excessive wear at startup. Again, we are discussing the needs of my single hypothetical engine for around town driving.
Oil type.. Thickness at 75 F ..Thickness at 212 F
Straight 30..........250....................10
10W-30...............100....................10
0W-30.................40.....................10
Straight 10..........30.....................6
Straight 5...........20.....................4
Straight 2...........15.....................3
Straight 0...........12.....................3 est.
A 10W-30 synthetic oil is based on a 30 weight oil. This is unlike the counterpart mineral oil based on a 10 weight oil. There is no VI improver needed. The oil is already correct for the normal operating temperature of 212 F. It has a thickness of 10 while you drive to work. It will never thin yet has the same long term problem as the mineral based oil. They both thicken with extended age.
Synthetic oils are derived in the laboratory. They are pure, usually nearly clear. I describe mineral based motor oils as a distilled, concentrated product. The impurities need to be removed from the raw petroleum. These oils are therefore less clean and contain many impurities. Again, the problem is really more of theory than practice but the difference does exist.
People repeatedly say that synthetic oils are more stable in a hot engine. I hear that they lubricate better. The answer is yes and no. Oil molecules do not break down, just the additives. Generally, the synthetic oils do not have VI improvers so have less to lose.
There are some properties of synthetic oils that actually result is less wear than with mineral oils. These help increase your gas mileage as well. Due to a reduction of internal friction of the synthetic oil your engine will run a bit cooler. Wear increases as temperature increases, all other things being constant.
A main advantage that the synthetic has over the mineral based oil is the ability to lubricate at startup. Both types of oil have the same specifications at 104 F, 212 F and 302 F. It is the startup viscosity characteristics that separate these oils. Synthetic oils do not thicken as much on cooling. They have better fluidity as the temperature drops.
A synthetic oil that is labeled as 10W-30 is less honey like as a mineral based 10W-30 motor oil at startup. They both have a thickness of 10 at normal operating temperatures. At 75 F the synthetic is not as thick. At 32 F the difference between the two is even greater. At 0 F the mineral oil is useless yet the synthetic works fairly well. Just keep the RPM to a minimum.
At temperatures below zero you will not be able to start your car with mineral oils while the synthetic oils may be used to -40 or - 50 F. Oils are so thick that the normal method of viscosity measurement is not possible. Instead we measure if the oil can even be pumped or poured. Again, we are only discussing a single category of oil, the multigrade 10W-30 API / SAE grade.
I took an except from the web about Mobil 1 oils. They compared a 5W-30 synthetic Mobil 1 oil to a mineral based 10W-30 and a 10W-40 in ice cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30 Mobil 1. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively. Neither of those engines started.
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.
To recap, synthetic oils have similar characteristics as mineral oils at operating temperatures. The synthetic oil will however be less honey - like at startup even though it has the same API / SAE rating. Yet the synthetic 10W-30 weight oil is based on a heavier 30 weight oil while the mineral based 10W-30 oil is based on a thinner 10 weight oil. They are both similar at operating temperatures yet the 30 weight based synthetic is actually less thick at startup and much less honey - like at low temperatures. This is the opposite of what common sense dictates.
This is worth repeating: The synthetic 10W-30 weight oil is based on a heavier 30 weight oil while the mineral based 10W-30 oil is based on a thinner 10 weight oil. They are both similar at operating temperatures yet the 30 weight based synthetic is actually less thick at startup and much less honey - like at low temperatures. This is the opposite of what common sense dictates.
As one can see this is no easy topic. Are you with me?</TD></TR></TBODY></TABLE>
Found this on a Ferrari site - probably more information than you need (or want) but it makes for an interesting read (the guy actually has 10 chapters devoted to this, but I only copied up to the part about synthetic oils.
