Is thicker synthetic run cooler?

[Brit33]

Originally Posted By: mechtech2
If thicker oil circulates slower, it wold have MORE time to pick up heat.
I can pass my hand through a bonfire quickly and not hardly feel it. A slow motion would burn me.


Very good point.
That is why they slow down the water pumps in high revving situations.
The water needs time to pick up the heat.

Too fast flow and it won't carry the heat away resulting in a heat build up.

Same principle can be applied to oil.

I have changed from 15w50 (factory specs) to 10w60 (due to bearing clearances) and haven't noticed any difference, just a better pressure at high revs and quieter cams/lifters especially at cold start ups.

 

[CATERHAM]

Originally Posted By: GMorg

And, thicker oil circulates slower ONLY when the the pump is in bypass mode. This is why thicker oil produces more pressure until the bypass is actuated.

Not true.
Thicker oil flows more slowly through an engine even when the oil pump is not in by-pass mode.
The reason thicker oil shows more oil pressure on an oil pressure gauge is because the OP gauge measures back pressure or the actual resistance to oil flow through an engine.
For example a 20W-50 will flow one gal/min less oil than a 0W-20
when the oil pump is not in by-pass. Of course if the oil is cold enough and therefore thick enough to activate the pressure release valve on the oil pump the oil flow will continue to decline.
BTW, depending on the engine, even with a light 0W-20, you'll still need at least 65-75C oils temp's to thin out the oil enough to avoid going into by-pass at elevated rev's. And another 20C to reach the optimum viscosity.

 

[FZ1]

Thinner runs cooler.

 

[GMorg]

Caterham: Help me understand your position.

The oil pumps that are familiar to me are gear pumps which are positive displacement pumps. In the absence of fluid slip past the gears, the output is fixed for a given rpm (given small clearances within the pump). The pressure differential and the viscosity of the fluid determines how much fluid slips past the gears (flow loss). With increase viscosity, the pressure differential is higher (as is oil pressure) but the fluid slip per unit of pressure is lower. With decreased viscosity, the fluid slip can increase, but the differential pressure is lower. For the range of viscosity used for PCMO, the differential pressure and the difference in viscosity seem to cancel-out each other.

The increase in oil pressure with higher viscosity fluids is due to the resistance force on flow, but not to lower flow. The observed pressure is a result of fixed fluid flow in the face of differences in viscosity.

Again, in bypass mode everything changes.

Through what mechanism does thinner oil flow faster from a positive displacement pump? I am not trying to argue. I am trying to understand the physics that must be invoked to see different flow rates from a fixed output pump.

 

[Brit33]

Originally Posted By: GMorg
Caterham: Help me understand your position.

The oil pumps that are familiar to me are gear pumps which are positive displacement pumps. In the absence of fluid slip past the gears, the output is fixed for a given rpm (given small clearances within the pump). The pressure differential and the viscosity of the fluid determines how much fluid slips past the gears (flow loss). With increase viscosity, the pressure differential is higher (as is oil pressure) but the fluid slip per unit of pressure is lower. With decreased viscosity, the fluid slip can increase, but the differential pressure is lower. For the range of viscosity used for PCMO, the differential pressure and the difference in viscosity seem to cancel-out each other.

The increase in oil pressure with higher viscosity fluids is due to the resistance force on flow, but not to lower flow. The observed pressure is a result of fixed fluid flow in the face of differences in viscosity.

Again, in bypass mode everything changes.

Through what mechanism does thinner oil flow faster from a positive displacement pump? I am not trying to argue. I am trying to understand the physics that must be invoked to see different flow rates from a fixed output pump.


I'm inlcined to believe you here also. The gears on the pump surely would pump the same amount of oil at the same rpm regardless of viscosity. It just takes a bit more force from the engine to pump the thicker stuff through the oil channels.

 

[CATERHAM]

Your correct that with a positive displacement oil pumps the output is fixed regardless of the viscosity of the oil for a given rpm.
An oil pressure gauge gauge measures the back pressure or resistance to oil flow through an engine. For a given engine rpm a lower viscosity oil provide a lower OP gauge reading than a higher viscosity oil because the resistance to flow through the engine (back pressure) is lower. This is because more oil is flowing through the engine.
It's also the reason why an OP gauge is an effective viscosity meter or viscometer.
The following artical on oil pumps also compares the different flow rates of a few oil grades (courtesy of Jeff_in_Vabch:
http://www.carcraft.com/techarticles/ccrp_0911_small_block_chevy_oil_pumps/viewall.html

 

[Mitch Alsup]

Actual data:
Vehicle: 1995 Ferrari F355
Conditions: Race track use at 100dF-103dF.
Oils: Redline 5W-30, 5W-40, 15W-50

These oils were tested over a several week period under as similar conditions as possible. The ambients were all typical of midSummer Texas heat paterns, the track was TWS just south of College Station Texas, running the same direction, and using the same tires, brake pads,... The car and driver are capable of lapping within 2 seconds of the lap record for the HP class and weight class of the car, considering street tires.

Results: 5W30 ran 2 degrees cooler than 5W-40. But 15W-50 ran 12 degrees hotter than 5W-40. Water temperatures remained between 225dF and 230dF.

I would call the 2 degrees cooler, insignificant and probably down close to the noise measurement floor, while I would say the 12 degrees hotter was significantly above the noise floor.

 

[Brit33]

Originally Posted By: Mitch Alsup
Actual data:
Vehicle: 1995 Ferrari F355
Conditions: Race track use at 100dF-103dF.
Oils: Redline 5W-30, 5W-40, 15W-50

These oils were tested over a several week period under as similar conditions as possible. The ambients were all typical of midSummer Texas heat paterns, the track was TWS just south of College Station Texas, running the same direction, and using the same tires, brake pads,... The car and driver are capable of lapping within 2 seconds of the lap record for the HP class and weight class of the car, considering street tires.

Results: 5W30 ran 2 degrees cooler than 5W-40. But 15W-50 ran 12 degrees hotter than 5W-40. Water temperatures remained between 225dF and 230dF.

I would call the 2 degrees cooler, insignificant and probably down close to the noise measurement floor, while I would say the 12 degrees hotter was significantly above the noise floor.


That is very significant. What's the factory recommendation for this engine?

I ran my alfa at 120 km.hr for an hour and the temp. never rose about 90 degrees C. with TWS 10w60. Would be interesting to see it run on 10w40. But 90 is a good temp for oil to keep it clean.

 

[GMorg]

Based on the viscosity chart, which shows averages, the SAE30 had had lower flow rate than the 20W50. The 0W10 had the SAME flow rate as the 0W20. Although the trend supports Caterham's conclusion, there are clearly other factors at play. This chart shows that sometimes a grade change does not affect flow rate, sometime thicker oil has higher flow, and sometimes thicker oil has lower flow. In addition, this data does not exempt measurements of flow when the bypass is active. I don't think that the chart proves the point.

I disagree that pressure is lower with lower viscosity due to lower flow. The pressure is lower due to less back pressure at a fixed flow. Clearly, flow can vary for the reasons described above. However, the pressure is the result of physical resistance to flow but not to flow rate.

 

[GMorg]

To correct the typo above,
I disagree that pressure is higher with higher viscosity due to lower flow.

 

[MolaKule]

Quote:
Which one absorb heat better? I would say syns right?



A fluid's temperature rises because thermal energy is put into it by transfer from the hot engine parts to the fluid. Thermal energy is transferred via conduction, radiation, or convection. Most heat transfer in an engine is done via convection and conduction. You can only allow a fluid to reach a certain temperature before it will change phase, in this case, to a vapor. So you have to conduct or convect this heat and transfer it to an oil cooler (convection) or to the oil pan (conduction).

Full synthetic oils have a slightly different specific heat value than does mineral oil, which means it has the potential to transfer thermal energy slightly better, all other things being equal.

Somewhere on here I did a calculation on just this topic but can't find it now.

The lower friction coefficient of full synthetic oils is what will show slightly lower temps than the specific heat value, assuming the same oil viscosity.

If you take a low viscosity oil and try to pump it through a pipe or orifice, it takes less energy to do so than with a higher viscosity oil. The increased mechanical energy to pump the thicker oil will result in this energy being transferred to the oil and the oil temperature will rise. In other words, it takes more mechanical energy to pump a thicker oil than a thinner oil.

 

[OVERKILL]

Originally Posted By: GMorg
To correct the typo above,
I disagree that pressure is higher with higher viscosity due to lower flow.


But that's exactly what the higher pressure means. Oil pressure is resistance to flow, higher pressure relative to another lubricant at the same temperature and RPM means less flow.

 

[KrisZ]

Originally Posted By: OVERK1LL
Originally Posted By: GMorg
To correct the typo above,
I disagree that pressure is higher with higher viscosity due to lower flow.


But that's exactly what the higher pressure means. Oil pressure is resistance to flow, higher pressure relative to another lubricant at the same temperature and RPM means less flow.


Something doesn't add up here. I think all it means is that the oil is thicker, and that there COULD be lees flow if the oil is significantly thicker.

If my fluid dynamics memory serves me right, which is a long shot,

, back pressure is directly related to flow and fluid viscosity, all else being equal.

So if you have a pipe with a constant diameter, it will always provide a certain back pressure that will be related to flow and fluid viscosity, just like oil system.

Let's say you're pumping water through that pipe. At certain flow the pipe will provide a certain back pressure and the only way to change that back pressure if to change flow. Higher flow will provide higher back pressure and vice versa. Now, if you want to pump oil through that same pipe and at the same flow, the back pressure will be higher than water because the oil is more viscous, but if you drop the flow, the back pressure will also drop, it has to because that's what the pipe sees. You cannot have lower flow with higher back pressure because that would mean that something else changed in the system, like the pump having not enough power to maintain flow.

I think you're confusing back pressure with pressure. Back pressure is like wind resistance, the faster you go (higher flow) the more drag (back pressure) the car will see. So if a compact car and an SUV go at the same speed, one will see less drag than the other, but simply looking at the drag (back pressure) will not tell you that the SUV is going slower. The SUV could see higher drag at a lower speed than the small compact, but that cannot be assumed by just looking at the drag value.

 

[TFB1]

Originally Posted By: KrisZ
You cannot have lower flow with higher back pressure because that would mean that something else changed in the system, like the pump having not enough power to maintain flow.


Got it, thank you!!!

Thicker oil flowing slower has been debunked, the higher pressure keeps oil flowing at same rate... Only if pressure climbed high enough to activate the bypass valve would flow be slower...

 

[Brit33]

Makes sense.
I get about 50 psi @3000 rpm with TWS 10w60 hot.
If I dropped to 10w40 I imagine the pressure would only reach about 30 psi @3000 rpm which would certainly concern me.
(15w50 was about 40psi @3000 rpm).
My bypass valve opens fully at 88 psi so I believe the fear of using thick oils is a myth. It only thins out less when hot.
If the pressure was over 70 psi then this would indicate the oil viscosity is getting a bit too much for the bearing clearances.

With the 10w60 I'm seeing oil temps of about 90 degrees (C) on the highway. I wouldn't want oil temps less than this as it wouldn't burn off all the contaminants.

Originally Posted By: TFB1
Originally Posted By: KrisZ
You cannot have lower flow with higher back pressure because that would mean that something else changed in the system, like the pump having not enough power to maintain flow.


Got it, thank you!!!

Thicker oil flowing slower has been debunked, the higher pressure keeps oil flowing at same rate... Only if pressure climbed high enough to activate the bypass valve would flow be slower...

 

[OVERKILL]

Originally Posted By: KrisZ
Originally Posted By: OVERK1LL
Originally Posted By: GMorg
To correct the typo above,
I disagree that pressure is higher with higher viscosity due to lower flow.


But that's exactly what the higher pressure means. Oil pressure is resistance to flow, higher pressure relative to another lubricant at the same temperature and RPM means less flow.


Something doesn't add up here. I think all it means is that the oil is thicker, and that there COULD be lees flow if the oil is significantly thicker.

If my fluid dynamics memory serves me right, which is a long shot,

, back pressure is directly related to flow and fluid viscosity, all else being equal.

So if you have a pipe with a constant diameter, it will always provide a certain back pressure that will be related to flow and fluid viscosity, just like oil system.

Let's say you're pumping water through that pipe. At certain flow the pipe will provide a certain back pressure and the only way to change that back pressure if to change flow. Higher flow will provide higher back pressure and vice versa. Now, if you want to pump oil through that same pipe and at the same flow, the back pressure will be higher than water because the oil is more viscous, but if you drop the flow, the back pressure will also drop, it has to because that's what the pipe sees. You cannot have lower flow with higher back pressure because that would mean that something else changed in the system, like the pump having not enough power to maintain flow.

I think you're confusing back pressure with pressure. Back pressure is like wind resistance, the faster you go (higher flow) the more drag (back pressure) the car will see. So if a compact car and an SUV go at the same speed, one will see less drag than the other, but simply looking at the drag (back pressure) will not tell you that the SUV is going slower. The SUV could see higher drag at a lower speed than the small compact, but that cannot be assumed by just looking at the drag value.




You are right. I got thinking about it again with no beer in me and a positive displacement pump moves X amount of fluid regardless. It is when the bypass comes into play (as indicated by the individual who posted after you) that what the SYSTEM sees changes.

At 30psi in the same system, a heavier oil will flow less than a lighter oil. However this would not occur at the same RPM (pump RPM). At a given RPM, regardless of pressure, as long as the bypass is not engaged, the same volume of lubricant will be seen by the system.

 

[Brit33]

I also find that using a lighter oil causes my hydraulic lifters to bleed out when oil is hot and start ticking (maybe due to the older housing design -1988) hence the need for the higher viscosity oils.
If I had mechanical tappets I would certainly use a lighter oil but that is not the case with my alfa.

Even if the flow is less(which was bunked already) with a 10w60 I need higher pressure for the tappets. (I had a costly cam/lifter replacement recently)
The OP is more important for the tappets than flow in my opinion, ok the bearings may be a little hotter but it's not used for racing and the temp never goes over 95c. (water 80-88)

 

[CATERHAM]

Originally Posted By: KrisZ
Originally Posted By: OVERK1LL
Originally Posted By: GMorg
To correct the typo above,
I disagree that pressure is higher with higher viscosity due to lower flow.


But that's exactly what the higher pressure means. Oil pressure is resistance to flow, higher pressure relative to another lubricant at the same temperature and RPM means less flow.


Something doesn't add up here. I think all it means is that the oil is thicker, and that there COULD be lees flow if the oil is significantly thicker.

If my fluid dynamics memory serves me right, which is a long shot,

, back pressure is directly related to flow and fluid viscosity, all else being equal.

So if you have a pipe with a constant diameter, it will always provide a certain back pressure that will be related to flow and fluid viscosity, just like oil system.

Let's say you're pumping water through that pipe. At certain flow the pipe will provide a certain back pressure and the only way to change that back pressure if to change flow. Higher flow will provide higher back pressure and vice versa. Now, if you want to pump oil through that same pipe and at the same flow, the back pressure will be higher than water because the oil is more viscous, but if you drop the flow, the back pressure will also drop, it has to because that's what the pipe sees. You cannot have lower flow with higher back pressure because that would mean that something else changed in the system, like the pump having not enough power to maintain flow.

I think you're confusing back pressure with pressure. Back pressure is like wind resistance, the faster you go (higher flow) the more drag (back pressure) the car will see. So if a compact car and an SUV go at the same speed, one will see less drag than the other, but simply looking at the drag (back pressure) will not tell you that the SUV is going slower. The SUV could see higher drag at a lower speed than the small compact, but that cannot be assumed by just looking at the drag value.

Yes GMorg is confusing the oil pump pressure and the back pressure that the an OP gauge measures.
Using your pipe analogy, the oil pump pressurizes the system or the pipe. At a given rpm the oil pump pressure is fixed regardless of the oil's viscosity. The fact that thicker oil results in more back pressure is measurement of the reduced oil flow. The thinking that the higher back pressure associated with pumping thicker oil will compensate fully and therefore flow at the same rate as lighter oil is simply not the case.

The oil grade comparison confirms this.
All testing was done below the oil pump by-pass point.
If we had the exact HTHSVs and VIs of the oils tested and not just the oil grades the differences between the light oils and heaviers oil would be more linear.

 

[GMorg]

I'm going to try again. The oil pump DOES NOT provide constant pressure at a given RPM. Positive displacement pumps provide constant flow at a fixed RPM (with the caveats described earlier). The pressure is higher at the pump and at the sending unit due to the resistance of the fluid to flow. The thicker the fluid, the more force that accumulates in the system, the more work that must be done at the pump, the more pressure that is seen at the sending unit. The flow is unchanged (at a given RPM). The pressures required to get that flow is changed. The energy that is wasted pumping is changed. The flow is not.

If you are given the task of moving a fluid through a pipe and the fluid flow must be constant, you will have to work harder to get a thick fluid through that pipe than if the fluid was less viscous. You would not have to turn the pump any faster. It would just be harder to turn.

 

[FZ1]

Originally Posted By: FZ1
Thinner runs cooler.
This^^^^^^^ Much adieu about nothing.