continued from the previous article:

RPM....Pressure..Flow
1,000......40 PSI....2
2,000......80 PSI....4
4,000....160 PSI....8 The maximum flow because of the oil pop off valve at 90 PSI will be 5
8,000... 320 PSI....16

Let us compare a 40 grade oil at operating temperature:
The oil is thicker, has more internal resistance and therefore requires more pressure to get the same flow (baseline engine).
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3
8,000....240 PSI....8

For a 40 grade oil at operating temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......45 PSI....1.5
2,000......90 PSI....3 The maximum flow because of the oil pop off valve at 90 PSI will be 3
4,000....180 PSI....6
8,000... 360 PSI....12

For a 40 grade oil at operating temperature
with the original pressures:
RPM....Pressure..Flow
1,000......20 PSI....0.5
2,000......40 PSI....1
4,000......80 PSI....2
8,000... 160 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3

Increasing the pressure while using the same oil will increase the oil flow but increasing the pressure by increasing the oil thickness will result in less flow. It takes more pressure to move a thicker oil. When you go to a thicker oil the pressure goes up because of the increased resistance, and therefore reduction of flow. Because the pressure is higher sooner, the relief valve cuts in sooner. Flow will actually be less when the RPM is up and the flow is needed the most.

There is more to these graphs but I will continue with the next chapter.

Furthermore, in review, pressure does not equal lubrication. Let us look again at a single closed “lifetime lubricated” bearing. We could hook up a system to pressurize the bearing. This can actually be done. We could have the oil at ambient pressure. We could then double, triple, quadruple the pressure of the oil. The oil is non-compressible. Regardless of the pressure we would have the exact same lubrication, that of the ambient pressure lubrication.

The physics of lubrication as I said earlier show a 1:1 relationship of flow to separation pressure. Lubrication itself is pressure independent. I will not go into the mathematical equations for this.

Even water can be used as a lubricant. This is partly because of its high surface tension. It is used in many medical devices and other systems that are under or exposed to water. It is just that water rusts metal parts making this unsuitable for automotive engines. It actually has a higher specific heat than oil. It can therefore carry away more heat than oil from bearing surfaces. In this respect water is a better lubricant than oil.

Motor Oil 201

I am going to bring up the constant flow pump concept. First, it goes back to the principal that doubling the pressure of the same grade oil does not exactly double the flow but it is close. Also doubling the RPM for the same reason does not exactly double the flow but again it is close.

This shows the problem best:

(A) For a 30 grade oil at operating temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off valve at 90 PSI will be 5

(B) For a 30 grade oil at operating temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......30 PSI....1.5
2,000......60 PSI....3
4,000....120 PSI....6 The maximum flow because of the oil pop off valve at 90 PSI will be 5
8,000... 240 PSI....12

If we stick with the same grade oil and increase the oil pump output we will increase the pressure and the oil flow too. If we double the oil pump output we will double the pressure and we will double the oil flow.

(C) For a 40 grade oil at operating temperature:
The oil is thicker, has more internal resistance and therefore requires more pressure to get the same flow. Compare this with (A):
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3
8,000....240 PSI....8

(D) For a 40 grade oil at operating temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......45 PSI....1.5
2,000......90 PSI....3 The maximum flow because of the oil pop off valve at 90 PSI will be 3
4,000....180 PSI....6
8,000... 360 PSI....12

The situations (A) and (C) are close to real life, assuming no loss in the system. This is what happens when you change the 30 grade oil to a 40 grade oil in your car:

(A) For a 30 grade oil at operating temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off valve at 90 PSI will be 5

(C) For a 40 grade oil at operating temperature:
The oil is thicker, has more internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3
8,000....240 PSI....8

At 6,000 RPM the maximum rate of flow has been reached with the thinner oil (A). When you go to 7, 8 or 9,000 RPM you do not get any more flow. You only get a maximum rate of 5. The internal forces on the bearings increase but there is no additional flow of oil.

With the thicker oil you reach maximum flow at 3,000 RPM (C). Worse yet is that the maximum flow is now only 3. As we increase RPM to 4, 5, 6, 7, 8, 9,000 RPM we get no additional pressure and no additional flow, no increase in lubrication.

Next let us look at a 20 grade oil at operating temperature. We get the same flow out of our constant volume pump but the thinner oil requires less pressure to move through the system. This even goes along with the rule that we should use an oil that gives us 10 PSI per 1,000 RPM:

(D) RPM....Pressure..Flow
1,000......10 PSI....1
2,000......20 PSI....2
4,000......40 PSI....4
8,000.. ...80 PSI....8

The maximum flow rate has not been reached. If the engine went to 9,000 RPM then the flow would be 9 at 90 PSI, our maximum pressure at pop off. The engine now has 3 times the flow rate as with the 40 grade oil at full RPM. The nozzles at the bottom of each cylinder are spraying 3 times the amount of oil lubricating and cooling this section. Everything runs cooler and the separation forces in the bearings are 3 times higher.

For engines that redline at 5,000 RPM they usually pop off the oil pressure at 50 to 60 PSI. For engines that go to 8-9,000 RPM the pressures max out at 90-100 PSI. You can now see that you can only get the maximum flow rate if you follow the 10 PSI / 1,000 RPM rule.

The winner: 0W-20 grade oil for my Maranello. I said earlier that I could have used a 10 grade oil. I actually only ran with 185 F oil temperatures around town and the pressures were similar to the 40 grade oil example in (C) above. This is why I also said that in the racetrack condition, with hotter, thinner (0W-20) oil, I may actually get the optimal results as in (D) above.

Now let us go back to the Ferrari recommended parameters in my 575 Maranello manual. It calls for 75 PSI at 6,000 RPM. The pop off pressure has not been reached. As we now increase the RPM we still get an increase in flow rate. This is what we need and this is exactly what they are recommending. We get our maximum flow at the maximum system pressure, at about the maximum engine RPM of 7,700. There is no bypassing of the oil. All oil pumped goes through the system. There is no wasted BHP pumping oil past the bypass valve back to the oil tank. It is the perfect system.

Finally I will compare a single, 30 grade oil, at normal (212 F) and at racetrack (302 F) temperatures:

(A) For a 30 grade oil at normal (212 F) operating temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off valve at 90 PSI will be 5

(E) For a 30 grade oil at elevated (302 F) operating temperature. The oil is thinner at 302 F. It requires less pressure to get the same flow:
RPM....Pressure..Flow
1,000......10 PSI....1
2,000......20 PSI....2
4,000......40 PSI....4
8,000......80 PSI....8 The maximum flow because of the oil pop off valve at 90 PSI will be 9

The hotter (302 F) 30 grade oil is thinner than the cooler (212 F) 30 grade oil. It has the same flow rate in the constant volume oil pump but at a lower pressure than the oil at normal operating temperature. This allows for a doubling of the flow rate at peak RPM. The thinning of oil at higher temperatures is a benefit. You get more flow, more cooling and more lubrication.

The 30 grade oil at 302 F has the exact same flow rate and pressures as the 20 grade oil at 212 F. See (D) above. Therefore, use the 20 grade for around town driving and the 30 grade on the hot track. You get maximum flow at each situation.

For YOUR engine, substitute the actual flow at 1,000 RPM. If your engine puts out 1.5 liters/min. at 1,000 RPM it would put out 3 liters/min. at 2,000 RPM and 6 liters/min. at 4,000 RPM and so on. The maximum flow in (A) would be 7.5 liters/min. In situations (D) and (E) you would get a maximum of 13.5 liters/min.

Conclusions:
The reason that multi-grade oils were developed in the first place was to address the problem of oil thickening after engine shutdown. Over the years we have been able to reduce the amount of thickening that occurs. Never-the-less there is no oil that does not thicken after you turn your engine off. This is why we have to warm up our engines before revving them up. Engine designers always pick the recommended oil based on a hot engine and hot oil. There is no issue with oil thinning as they are both matched when hot. The problem is oil thickening when the engine cools.

Cold engine showing very high pressures because of the thickened oil at startup:

For a 40 grade oil at 75 F at startup:
The oil is thicker, has more internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......60 PSI....1
2,000....120 PSI....2 The maximum flow because of the oil pop off valve at 90 PSI will be 1.5
4,000....240 PSI....4
8,000....480 PSI....8

At 1,500 RPM you reach the maximum oil flow rate and if you run to 8,000 RPM it is the same rate. The flow cannot increase and it is insufficient. This is why we must wait until our oil temperature comes up to 212 F or higher. The maximum flow rate in this case will then double, up to 3. To get even more flow in our test engine you need to use a lower viscosity grade.

If you have absorbed and digested the information here you should be able to pick out the proper operating oil grade for your car, be it a 30, 40, 50 or even 20 grade oil. I have always used oils that were a grade thinner than recommended even though many use a grade thicker than recommended. I showed evidence that the starting grade should always be 0 or 5 (0W-XX or 5W-XX for thicker oils). If you want the best protection and highest output from your motor use a synthetic based oil. The actual brand is not as critical as the viscosity. The rating must be the SL or SM rating. Change your oil every 3 - 5,000 miles and at least every spring.

THE END

Here's the test if you are interested...

Motor Oil Midterm Examination
Answer questions without looking back. This is a closed book exam. Base your answers on the information provided in these past chapters.

1- At normal operating temperature, 212 F, a straight 30 grade oil has a viscosity of how many centiStokes?
A- 3
B- 6
C- 10
D- 20
E- 30

2- While racing at 95 F, mid-summer in Florida, which of these synthetic oils gives the best protection at 302 F oil temperature?
A- 0W-40
B- 5W-40
C- 10W-40
E- They are all exactly the same

3- While starting up your car at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight 10 (ten) grade motor oil?
A- 3 cS
B- 6 cS
C- 10 cS
D- 20 cS
E- 30 cS or higher

4- The biggest problem with mineral based motor oils with long term use is:
A- Thinning
B- Thickening
C- Loss of VI (viscosity index) improvers
D- Both A and C
E- None of the above is correct

5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
D- All of the above
E- None are too thick

Answers to the Oil Midterm Exam
I feel these were all difficult questions. You would be doing well to get 3 correct.

1- At normal operating temperature, 212 F, a straight 30 grade oil has a viscosity of how many centiStokes?
A- 3
B- 6
C- 10
D- 20
E- 30
The correct answer is C- 10 cS.

2- While racing at 95 F, mid-summer in Florida, which of these synthetic oils gives the best protection at 302 F oil temperature?
A- 0W-40
B- 5W-40
C- 10W-40
E- They are all exactly the same
The correct answer is E- They are all exactly the same.

3- While starting up your car at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight 10 (ten) grade motor oil?
A- 3 cS
B- 6 cS
C- 10 cS
D- 20 cS
E- 30 cS or higher
The correct answer is E- 30 cS or higher.

4- The biggest problem with mineral based motor oils with long tern use is:
A- Thinning
B- Thickening
C- Loss of VI (viscosity index) improvers
D- Both A and C
E- None of the above is correct
The correct answer is B- Thickening

5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
D- All of the above
E- None are too thick
The correct answer is D- All of the above

Motor Oil Final Examination
Answer questions without looking back. This is a closed book exam. Base your answers on the information provided in these past chapters.

1- While starting up your car at 75 F, mid-winter in Florida, which of these synthetic oils provides the least startup resistance, minimal battery and starter motor load?
A- 0W-20
B- 0W-30
C- 0W-40
D- 0W-50
E- They are all exactly the same

2- While vacationing in Orlando, it is 104 F mid-summer in Florida. The rental car company put a straight mineral based 30 grade oil in their car because they wanted the operating temperature viscosity to be at 10 cS. What will be the approximate viscosity of the oil when you start up your engine now? (Closest answer)
A- 10 cS
B- 20 cS
C- 30 cS
D- 100 cS
E- 400 cS

3- While vacationing in Florida you are able to race your car at the Sebring track. At an oil temperature of 302 F what is the approximate difference in viscosity between a 20 and 40 grade oil. (Pick the closest number)
A- 1
B- 10
C- 20
D- 40
E- 400

4- Assume there are no losses in the system and your oil pump is truly volume based. Also assume there is no cut off pressure valve and you are using a 40 grade motor oil. If at 1,000 RPM your pressure is 30 and your pump output is 1 (one), what will the pressure and output be at redline, 8,000 RPM?
A- 240 PSI, flow = 8
B- 180 PSI, flow = 8
C- 240 PSI, flow = 4
D- 180 PSI, flow = 4
E- 120 PSI, flow = 8

5- Water can be used as a lubricant.
A- True
B- False

6- If you increase the pressure in a bearing, all other things being constant, the force of separation between the parts increases.
A- True
B- False

7- The best grade oil for racing any Ferrari or Lamborghini is a 40 grade multi-grade synthetic oil like Mobil One 0W-40.
A- True
B- False

8- For my Maranello 575 the 0W-20 grade Mobil 1 oil was actually too thick for my driving conditions.
A- True
B- False

9- The major problem with engine oil is that it thins with increasing temperature.
A- True
B- False

10- Your 1993 sports car manual states to use an API / SAE SH rated 10W-40 mineral based motor oil. Your engine has only 1,550 miles on the odometer. On your next oil change it would be better to use a SM rated 0W-40 synthetic oil.
A- True
B- False

11- According to SAE J300 a 30 grade oil has a viscosity of between 9.3 and 12.4 centiStokes at operating temperature (212 F).
A- True
B- False

12- In my list of recommended oils what did I list as the best mineral based motor oil in the 50 grade class?
B- Castrol GTX 15W-50
C- Red Line 10W-50
D- Valvoline Durablend 0W-50
E- No oil was recommended

13- You are running 5W-40 Shell Helix Ultra fully synthetic motor oil in your Mercedes Benz. You are in a K-Mart shopping center and checked your oil and it is 1 1/2 quarts low. You will need to add one can of oil. Which of the following is the best choice.
A- Mobil 1 - 0W-40
B- Pennzoil Synthetic 5W-40
C- Red Line Synthetic 5W-40
D- Castrol Syntec 0W-30
E- Shell mineral based 10W-40

14- Motor oils that are labeled “for racing only” should not be used for everyday driving because:
A- They do not have detergents
B- They may have harmful levels of some additives
C- They are generally unrated, there is no SJ, SL or SM approval
D- You would have to take your engine apart and clean it periodically
E- All of the above

15- ASTM stands for:
A- Automotive Standards and Test Methods
B- Automotive Society for Tooling and Machining
C- American Society for Testing and Materials
D- American Standards Trade and Manufacturing
E- Society for American Standard Testing Methods

16- If your engine is running too hot at higher RPM one thing you can try to bring the temperature down is to use a thinner oil.
A- True
B- False

17- Oil with a startup thickness of 100 (at 75 F) that becomes the appropriate thickness of 10 when fully warmed up (212 F) is called a 10W-30 grade motor oil.
A- True
B- False

18- A main advantage that the synthetic has over the mineral based oil of the same grade is the ability to lubricate better at startup.
A- True
B- False

19- In ASTM D 4485 3.1.4: Engine oil is defined as - - “a liquid that reduces friction and wear between moving parts within an engine, and also serves as a coolant.”
A- True
B- False

20- I am (single best answer):
A- Surgeon
B- Biochemist
C- ‘Halfass mechanic
D- Absurdly interested in motor oils
E- All of the above

Answers to the Oil Final Exam
I feel these were all very difficult questions. You would be doing well to get 10 correct.

1- While starting up your car at 75 F, mid-winter in Florida, which of these synthetic oils provides the least startup resistance, minimal battery and starter motor load?
A- 0W-20
B- 0W-30
C- 0W-40
D- 0W-50
E- They are all exactly the same
The correct answer is A- 0W-20.

2- While vacationing in Orlando, it is 104 F mid-summer in Florida. The rental car company put a straight mineral based 30 grade oil in their car because they wanted the operating temperature viscosity to be at 10 cS. What will be the approximate viscosity of the oil when you start up your engine now?
A- 10 cS
B- 20 cS
C- 30 cS
D- 100 cS
E- 400 cS
The correct answer is D- 100 cS

3- While vacationing in Florida you are able to race your car at the Sebring track. At an oil temperature of 302 F what is the approximate difference in viscosity between a 20 and 40 grade oil. Pick the closest number.
A- 1
B- 10
C- 20
D- 40
E- 400
The correct answer is A- 1

4- Assume there are no losses in the system and your oil pump is truly volume based. Also assume there is no cut off pressure valve and you are using a 40 grade motor oil. If at 1,000 RPM your pressure is 30 and your pump output is 1 (one), what will the pressure and output be at redline, 8,000 RPM?
A- 240 PSI, flow = 8
B- 180 PSI, flow = 8
C- 240 PSI, flow = 4
D- 180 PSI, flow = 4
E- 120 PSI, flow = 8
The correct answer is A- 240 PSI, flow = 8

5- Water can be used as a lubricant.
A- True
B- False
The correct answer is A- True

6- If you increase the pressure in a bearing, all other things being constant, the force of separation between the parts increases.
A- True
B- False
The correct answer is B- False

7- The best grade oil for racing any Ferrari or Lamborghini is a 40 grade multi-grade synthetic oil like Mobil One 0W-40.
A- True
B- False
The correct answer is B- False. It can best be determined by driving the car with one type of oil and follow the pressures and temperatures of your oil.

8- For my Maranello 575 the 0W-20 grade Mobil 1 oil was actually too thick for my driving conditions.
A- True
B- False
The correct answer is A- True

9- The major problem with engine oil is that it thins with increasing temperature.
A- True
B- False
The correct answer is B- False. The problem is thickening when the engine is turned off. With long term use the problem is also thickening. Engine oils grades are matched at operating temperature. It is after the engine cools that viscosities are an issue.

10- Your 1993 sports car manual states to use an API / SAE SH rated 10W-40 mineral based motor oil. Your engine has only 4,550 miles on the odometer. On your next oil change it would be better to use a SM rated 0W-40 synthetic oil.
A- True
B- False
The correct answer is A- True. Although it may actually be preferential to use a modern 0W-30 grade oil.

11- According to SAE J300 a 0W-30 and a straight 30 grade oil must have a viscosity of between 9.3 and 12.4 centiStokes at operating temperature (212 F).
A- True
B- False
The correct answer is A- True

12- In my list of recommended oils what did I list as the best mineral based motor oil in the 50 grade class?
B- Castrol GTX 20W-50
C- Red Line 15W-50
D- Valvoline Durablend 20W-50
E- No oil was recommended
The correct answer is E- No oil was recommended. They all are too thick at startup for daily use.

13- You are running 5W-40 Shell Helix Ultra fully synthetic motor oil in your Mercedes Benz. You are in a K-Mart shopping center and checked your oil and it is 1 1/2 quarts low. You will need to add one can of oil now. Which of the following is the best choice.
A- Mobil 1 - 0W-40
B- Pennzoil Synthetic 5W-40
C- Red Line Synthetic 5W-40
D- Castrol Syntec 0W-30
E- Shell mineral based 10W-40
The correct answer is E- Shell mineral based 10W-40. You can mix any SM rated oil in there but this is my first choice based on my research.

14- Motor oils that are labeled “for racing only” should not be used for everyday driving because:
A- They do not have detergents
B- They may have harmful levels of some additives
C- They are generally unrated, there is no SJ, SL or SM approval
D- You would have to take your engine apart and clean it periodically
E- All of the above
The correct answer is E- All of the above

15- ASTM stands for:
A- Automotive Standards and Test Methods
B- Automotive Society for Tooling and Machining
C- American Society for Testing and Materials
D- American Standards Trade and Manufacturing
E- Society for American Standard Testing Methods
The correct answer is C- American Society for Testing and Materials

16- If your engine is running too hot at higher RPM one thing you can try to bring the temperature down is to use a thinner oil.
A- True
B- False
The correct answer is A- True

17- Oil with a startup thickness of 100 (at 75 F) that becomes the appropriate thickness of 10 when fully warmed up (212 F) is called a 10W-30 grade motor oil.
A- True
B- False
The correct answer is A- True

18- A main advantage that the synthetic has over the mineral based oil of the same grade is the ability to lubricate better at startup.
A- True
B- False
The correct answer is A- True

19- In ASTM D 4485 3.1.4: Engine oil is defined as - - “a liquid that reduces friction and wear between moving parts within an engine, and also serves as a coolant.”
A- True
B- False
The correct answer is A- True

20- I am (single best answer):
A- Surgeon
B- Biochemist
C- ‘Halfass mechanic
D- Absurdly interested in motor oils
E- All of the above
The correct answer is E- All of the above

For More See:

FerrariChat.com - FAQ: Motor Oil Articles by Dr. Ali E. Haas (AEHaas)