Motor Oil 201
Chapter 10, The graduate.
I am going to again 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 in the Ferrari:
(A) For a 30 grade oil at normal 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 But: The maximum flow (because of the oil pop off bypass valve at 90 PSI ) will be 5. There are people who say the pressure is not limited and that it still increases as the RPM goes up. This is not my experience in any car I have owned. The pressure goes up to but not past the set relief pressure. If the pressure cannot increase, the flow cannot increase, plain physics.
(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. But only to the point where the bypass pressure is reached. As shown, the high output pump is still limited to the same flow as the lower output pump when bypass is reached.
(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. In no car I owned has the pressure increased above the maximum relief valve pressure despite increasing RPM. 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 may be higher.
For engines that redline at 5,000 RPM they usually pop off the oil pressure at 40 to 50 PSI. For engines that go to 8-9,000 RPM the pressures max out at 70-90 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.
Today they are making some variable rate oil pumps. This is so they only pump what can be used by the system (still pressure limited). There will be less waste of energy to pump oil that only ends up back in the sump because it was in bypass. The pump itself may also be protected from Cavitation wear and tear.
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. And the problem is not just for the first minute after start up. Remember that oil heats up slowly so 5 minutes later we still have almost the same pressures and flow with just a little improvement.
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 or get the engine oil to an even higher temperature..
Again, these examples are real. In all my cars the oil pressure rises linearly until the oil pump relief pressure is hit. Then there is no additional increase in pressure and there can be no additional increase in flow. When an oil is thicker by grade or by lowered temperature the relief pressure comes into play earlier resulting in limited flow. Engine damage occurs when people rev them up before the oil has warmed up to the normal operating temperature. And this damage occurs at moderate temperatures as 75 F, not even really cold temperatures.
The new stop-start engine “feature’ of many cars results in slower engine warming and has led to issues potentially causing wear, sludge, and varnish formation. New and thinner oils are being developed to protect better from these issues.
Big diesel railroad locomotive engines have been using straight 40 grade oils for years. But they have started using 20W-40 grade multi-viscosity oils and most are zinc free. Interesting that they are now concerned about thinner start up viscosities even though these engines are infrequently turned on and off.
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. But I have never used the car or truck to its full capacity of power.
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 should be the SN or SP. Change your oil every 4 - 5,000 miles if you are stressing your oil and at least every spring.
AEHaas
These chapters are based on my research, experimentation and experience.
Chapter 10, The graduate.
I am going to again 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 in the Ferrari:
(A) For a 30 grade oil at normal 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 But: The maximum flow (because of the oil pop off bypass valve at 90 PSI ) will be 5. There are people who say the pressure is not limited and that it still increases as the RPM goes up. This is not my experience in any car I have owned. The pressure goes up to but not past the set relief pressure. If the pressure cannot increase, the flow cannot increase, plain physics.
(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. But only to the point where the bypass pressure is reached. As shown, the high output pump is still limited to the same flow as the lower output pump when bypass is reached.
(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. In no car I owned has the pressure increased above the maximum relief valve pressure despite increasing RPM. 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 may be higher.
For engines that redline at 5,000 RPM they usually pop off the oil pressure at 40 to 50 PSI. For engines that go to 8-9,000 RPM the pressures max out at 70-90 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.
Today they are making some variable rate oil pumps. This is so they only pump what can be used by the system (still pressure limited). There will be less waste of energy to pump oil that only ends up back in the sump because it was in bypass. The pump itself may also be protected from Cavitation wear and tear.
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. And the problem is not just for the first minute after start up. Remember that oil heats up slowly so 5 minutes later we still have almost the same pressures and flow with just a little improvement.
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 or get the engine oil to an even higher temperature..
Again, these examples are real. In all my cars the oil pressure rises linearly until the oil pump relief pressure is hit. Then there is no additional increase in pressure and there can be no additional increase in flow. When an oil is thicker by grade or by lowered temperature the relief pressure comes into play earlier resulting in limited flow. Engine damage occurs when people rev them up before the oil has warmed up to the normal operating temperature. And this damage occurs at moderate temperatures as 75 F, not even really cold temperatures.
The new stop-start engine “feature’ of many cars results in slower engine warming and has led to issues potentially causing wear, sludge, and varnish formation. New and thinner oils are being developed to protect better from these issues.
Big diesel railroad locomotive engines have been using straight 40 grade oils for years. But they have started using 20W-40 grade multi-viscosity oils and most are zinc free. Interesting that they are now concerned about thinner start up viscosities even though these engines are infrequently turned on and off.
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. But I have never used the car or truck to its full capacity of power.
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 should be the SN or SP. Change your oil every 4 - 5,000 miles if you are stressing your oil and at least every spring.
AEHaas
These chapters are based on my research, experimentation and experience.