[sgiitk]

Originally Posted by Jeroen

No, thinner is not better, at some point thinner gets worse. As most oil pumps are positive displacement type thinner doesn't circulate faster perse.

Remembet we re talking of cold oil, which is far thicker than hot oil. The viscosity drops by orders of magnitude as you get hot. Thus 0W (actually more like 2-3W, since 0W is like a zero watt bulb, not achievable in reality) is thicker than 40 (hot). So the pump does work better on the thinner (cold) oil. Also, most cars have hydraulic lifters, so against faster circulation will help. Also, which in the days of Oil pressure gauges, I saw 70-80psi on cold oil, never saw anything like that on hot oil.

[bullrun87]

Realistically positive displacement pumps are not significantly affected by changes in viscosity. So a slightly thinner/ thicker oil will not significantly affect the flowrate/efficiency of these pumps. But sometimes you just have to deviate from manufacturer recommended specifications in order to use a better oil. So for example if my manual recommends 15w40 and I wish to use only synthetic oil for my ride, I usually have to choose either 5w40/ 0w40/ 0w50. I strongly believe that even though I have deviated from the manufacturer recommendations I am actually treating the engine better since I am using better quality synthetic oil

[sgiitk]

Originally Posted by bullrun87

So for example if my manual recommends 15w40 and I wish to use only synthetic oil for my ride, I usually have to choose either 5w40/ 0w40/ 0w50.

I will prefer the 5W40 or 0W40 for marginally better economy.

[Jeroen]

Originally Posted by sgiitk

Remembet we re talking of cold oil, which is far thicker than hot oil. The viscosity drops by orders of magnitude as you get hot. Thus 0W (actually more like 2-3W, since 0W is like a zero watt bulb, not achievable in reality) is thicker than 40 (hot). So the pump does work better on the thinner (cold) oil. Also, most cars have hydraulic lifters, so against faster circulation will help. Also, which in the days of Oil pressure gauges, I saw 70-80psi on cold oil, never saw anything like that on hot oil.

No, the pump does not work better. As pointed out before positive displacement pumps volumes are not, or hardly at all, affected by viscosity. The 70-80 psi on a cold engine is quite normal. On a little side note, the oil pressure is the best indication for the overall engine having been heated up to normal working temperatures. Never use the cooling water temperature for that. As very few cars have oil temperature indicators, pressure is the next best thing.

Engine oil serves a number of different purposes, chief amongst which not surprisingly lubrication. In this and other related thread people talk about for instance the proper lubrication of the various bearings. Truth be told, that is an area where you dont need to worry. You would be very hard pressed to find on this or other car forums a major engine bearing problem related to the quality or the specification of oil. Those few cases of serious problems is usually related to no or to little oil, a seized oil pump (i.e. No oil) or something blocking the oil inlet etc.

The engine parts that will always have the most wear and tear are in fact the piston, piston rings and cilinder liners. They are typically splash lubrication, piston movement is inline, from zero to max velocity and back to zero again. Top of the piston and the piston rings are open to the combustion chamber etc. etc.

So at the best of time a very difficult to get proper lubrication. You can open up any engine with 100-150.000 km and you are very likely not to find any wear on bearings, but you will always find significant wear and tear on piston, piston rings and the cilinder liners.

Most waer and tear happens during the first 5-10 minutes of an engine being started and warming up to its normal operating temperatures. A couple of hours driving on the motorway is likely to result in less wear and tear then those first 5-10 minutes of after engine start. I have posted somewhere on this forum my own hands on experience on empirical research into lubrication. You will find the same conclusion, cylinder temperature had a huge impact on wear.

The lubrication of the piston, piston rings and cilinder is amongst others a function of the cilinder liner temperature. So it is really important to have the most optimum viscosity during those first 5-10 minutes. So I don't think it is prudent to deviate from the manufacturer recommendation. If you think differently, please show me statistically significant measurements, showing no negative effects as a result of using thinner oil during engine warm up period.

In general discussing the properties and effect of different lub oils on car forums is completely devoid of any real live measurements as far as wear and tear is concerned. You need to take a lot of measurements and you need to take the respective engines apart a lot. Otherwise its at best just individual opinions based on no factual data.

This whole discussion also shows that very few people have a good understanding on what contributes to wear and tear and what parts are most susceptible to wear and tear under what circumstance. Again, offering advise without pointing out such factors i believe needs to be avoided.

Waer and tear, even with the best of lub oils is normal and can't really be avoided. Understanding what wears under what condition should br understood before making any changes in changing oil specifications.

On the upside, most car engines these days are pretty robust. To put it differently, even if you don't use the correct oil and or correct oil specification it might be quite a while before real problems occur. Never the less, I am an engineer at heart and I will stick to what the manufacturer recommends unless I have hard proof, statistically significant evidence to the contrary. On that note, the research I mentioned before was to figure out, scientifically, to find out if the expensive lub oil brands did a better job then the B-Brands. Our conclusion was they did not. When confronted by our research data the involved oil manufacturer gave us a huge discount which brought their price at a similar level as the B-brands.

stick to the manufacturers recommendation. if anything because people like me never buy cars with less then 150.000 km on the clock. That's the point where you will see the evidence of lub oil quality if any at all. Exception to the rule is cars which are used on relative short trips, ie lots of start ups. A five year old car with 200.000 km on the clock is likely to be in much better condition, engine wise then a car that has done 30.000 km in five years. Open up a few engines and measure the cilinder liners and you will find it holds true.

Jeroen

[khoj]

Cold oil will have higher viscosity and as viscosity increases, slip decreases and the liquid is able to better fill up the clearances thereby the volumetric efficiency of a pd pump increases. Of course that also means higher line losses and increased power requirements & such but then that is another tangent.

Originally Posted by sgiitk

So the pump does work better on the thinner (cold) oil.

The statements below are like smoking guns.

When read in a scenario where pd pumps are being compared to centrifugals they hold. However when these are read for pd pumps in isolation they are not entirely correct.

Originally Posted by bullrun87

Realistically positive displacement pumps are not significantly affected by changes in viscosity. So a slightly thinner/ thicker oil will not significantly affect the flowrate/efficiency of these pumps.

Originally Posted by Jeroen

No, the pump does not work better. As pointed out before positive displacement pumps volumes are not, or hardly at all, affected by viscosity.

As far as I know pd pump usage for engine lubrication is limited mainly to engines with dry sump design or let's say very large engines. Earlier external gear design was being commonly used in automotive applications but increasingly car OEMs prefer to use centrifugals 'cause any given day they are far more economical to manufacture compared to pd pumps.
That is my understanding & my resultant query is whether it is relevant to make pd pumps & the effects of changes in the oil's viscosity on them the basis of this discussion pertaining to four wheeler engines?

[Jeroen]

Originally Posted by khoj

Cold oil will have higher viscosity and as viscosity increases, slip decreases and the liquid is able to better fill up the clearances thereby the volumetric efficiency of a pd pump increases. Of course that also means higher line losses and increased power requirements & such but then that is another tangent.





The statements below are like smoking guns.

When read in a scenario where pd pumps are being compared to centrifugals they hold. However when these are read for pd pumps in isolation they are not entirely correct.





As far as I know pd pump usage for engine lubrication is limited mainly to engines with dry sump design or let's say very large engines. Earlier external gear design was being commonly used in automotive applications but increasingly car OEMs prefer to use centrifugals 'cause any given day they are far more economical to manufacture compared to pd pumps.
That is my understanding & my resultant query is whether it is relevant to make pd pumps & the effects of changes in the oil's viscosity on them the basis of this discussion pertaining to four wheeler engines?

Not sure I agree with your first statement. Please note that lots of rotary pumps are PD pumps and not centrifugal pumps. And yes, centrifugal pumps are cheaper than PD pumps. But they have at least one major drawback compared to PD pumps. By themselve a centrifugal pump is not self priming. So if you want to use a centrifugal pump in a car engine its needs to be positioned in such a way that the oil feeds into the actual pump house by gravity or you need to find another way of creating initial vacuum to prime on start up. On large diesels such as in marine application you will often find the oil pumps driven separately by e-motors. Some of those pumps Ive sailed with were centrifugal pumps, but with special provisions for the priming.

I own four cars at present and every single one has a PD oil pump. Usually some type of gear and or worm type. Rotary pump, but still a PD type. Just check this image, is it a centrifugal or a PD pump? http://aquaskier.com/articles/impeller_rotation.gif

Centrifugal pumps are more affected by viscosity then PD pumps. Either way, whatever is fitted to your engine, it is a conscientious choice of the design team and they would have taken all pump characteristics into consideration.

Irrespective of pump design I maintain you should not deviate from manufacturer recommendation unless you have a very thorough understanding of the (possible) issues at hand and have sufficient and meaningful data to reach a different conclusion then the manufacturer's design team.

One final comment on viscous oil not filling all edges/crevices in a PD pump. When that happens you will know more or less immediately. Because within seconds your oil will turn into foam. It has happened tome several times over on hydraulic systems on cranes, winches, forklifts etc. last time it even happened to me when I replaced the steering pump on My Mercedes. Its a cmbination of low pressure (ie vacuum) in combination with air molecules entrapped in the oil and the oils viscosity. Makes a huge mess.

Jeroen

[khoj]

That's Ok, I stand by what I have posted.

The picture is a doozy, the first glance giving a semblance of an impeller but then the eccentric placement for the shaft and the almost 'not there' crescent point towards a flexible vane design a pd pump. Confirmed by what else but the flexing vanes. BTW besides rotary there are quite a few reciprocating PD pumps too.

As I posted, cars earlier used to have pd pumps. IIRC your cars are from the "design over pennies" era.

I believe the phenomenon that you are describing is called cavitation and yes when a pd pump cavitates it is Diwali and July 4th fireworks rolled in to one.

I concur that the manufacturer's recommendations are best not taken lightly. However, we humans are at times inquisitive and mostly vain and therefore our oddball selections on stuff we think is best for, dare I say the World at large.

Originally Posted by Jeroen

I own four cars at present and every single one has a PD oil pump. Usually some type of gear and or worm type. Rotary pump, but still a PD type. Just check this image, is it a centrifugal or a PD pump? http://aquaskier.com/articles/impeller_rotation.gif


One final comment on viscous oil not filling all edges/crevices in a PD pump.

[bullrun87]

Originally Posted by khoj

Cold oil will have higher viscosity and as viscosity increases, slip decreases and the liquid is able to better fill up the clearances thereby the volumetric efficiency of a pd pump increases. Of course that also means higher line losses and increased power requirements & such but then that is another tangent.
As far as I know pd pump usage for engine lubrication is limited mainly to engines with dry sump design or let's say very large engines.

I completely agree with your assessment of PD pumps. But I have never heard of centrifugals being employed for engine oil circulation. I only know of gear pumps and vane type pumps being used in this application. Could you give an example of the use of a centrifugal for circulating engine oil? Are cars we see everyday using PD's or centrifugals? I ask this because in my experience the efficiency of centrifugals falls off rapidly if viscosity of fluid is over certain limits and quite frankly I dont think I have ever seen a centrifugal being used for circulating any sort of lubricating oil.

[Jeroen]

Originally Posted by khoj

That's Ok, I stand by what I have posted.

Be my guest, but the evidence to the contrary is utterly overwhelming. Check out Wikipedia, or google images for car engine oil pump and you see you are completely wrong with your centrifugal pumps for car engines. Also, please explain how you will go about them not priming themselves and how to solve that in your typical car engine application. I won't be holding my breath.

Originally Posted by khoj

The picture is a doozy, the first glance giving a semblance of an impeller but then the eccentric placement for the shaft and the almost 'not there' crescent point towards a flexible vane design a pd pump. Confirmed by what else but the flexing vanes. BTW besides rotary there are quite a few reciprocating PD pumps too.

Correct it is a PD pump, often mistaken for a centrifugal pump. Sure there are reciprocating PD pumps out there. I've designed, commissioned them and overhauled them many a times. But reciprocating PD pumps as oil pump on a car engine, I don't think I have come across.

Originally Posted by khoj

As I posted, cars earlier used to have pd pumps. IIRC your cars are from the "design over pennies" era.

See the above, trust me google images of car engine oil pump and you will find hundreds if not thousands of PD pumps, not centrifugal ones.

Originally Posted by khoj

I believe the phenomenon that you are describing is called cavitation and yes when a pd pump cavitates it is Diwali and July 4th fireworks rolled in to one.

No its not, cavitation is a very different phenomena, although it does also start with very local low pressure areas, releasing gasses that subsequently implode on the pressure building up as the gas bubbles move along the surface of the impeller/propellor whatever. it can happen on ship propellors, but also on the impellers of for instance centrifugal pumps. It shows as pitting on the impeller/propellor and can destroy it completely. However, it doesn't necessarily impact the normal operation of the pump. That is up to the moment where the impeller is really damaged and bits begin to fall off. So its a real concern to designers. I have overhauled dozens and dozens of pumps and nearly always the impellers of centrifugal pumps had more or less evidence of cavitation. I have seen impellers more than half eaten away by cavitation. Much to my surprise these pumps were working fine. With sufficient pressure and flow. Which might indicate they were heavily over dimensioned in the first place.

What I described earlier is simple foaming of the oil. Much more destructive, if you are not careful as you loose all oil pressure immediately. Whereas cavitation is really an occurrence on a micro level at certain parts of the impeller/propellor, foaming occurs across a large part of the impeller/propellor/worm whatever. Its' best compared by sticking a mixer into a think viscous fluid and see what happens. It will start foaming. Once it starts foaming there is nothing you can do. You need to shut down the engine immediately as the oil pump will simply not work anymore. Then you might have to wait for hours, if not days for the foam to settle and turn back into normal regular oil. Its all down to viscosity/temperature and how fast the pump turns etc. So the only thing you can do to prevent is to heat the oil. So we installed heaters in our cranes on the hydraulic reservoir. We kept blankets wrapped around reservoirs and pumps etc.

You need to be particularly careful after maintenance if you have drained the complete circuit and start refilling it. PD pumps are self priming, but if the oil is to thick, it won't fill the pump quickly enough and this might happen. I've had it happen to me a number of times.

Originally Posted by khoj

I concur that the manufacturer's recommendations are best not taken lightly. However, we humans are at times inquisitive and mostly vain and therefore our oddball selections on stuff we think is best for, dare I say the World at large.

You're telling me. I know of people who fool heartily, against overwhelming evidence, insist on their own stories/opinion without even showing their own data to substantiate their claim. For instance, they would say, most car engine have centrifugal oil pumps, but fail to substantiate their claim. How silly is that?

Originally Posted by bullrun87

I completely agree with your assessment of PD pumps. But I have never heard of centrifugals being employed for engine oil circulation. I only know of gear pumps and vane type pumps being used in this application. Could you give an example of the use of a centrifugal for circulating engine oil? Are cars we see everyday using PD's or centrifugals? I ask this because in my experience the efficiency of centrifugals falls off rapidly if viscosity of fluid is over certain limits and quite frankly I dont think I have ever seen a centrifugal being used for circulating any sort of lubricating oil.

I completely agree with you. Just so everybody understands, gear and vane pumps are PD pumps. On car engines, the fast majority uses some sort of PD pump. I have seen centrifugal pumps being used on engines as I stated earlier, but not on car engines.

The viscosity point you bring up is true and as I mentioned before another real short fall is their inability of self priming.

Jeroen

[Jeroen]

a little empirecal test:

Do a google image search for "car engine oil pump"

You will get hundreds if not thousands of hits. Now count the number of centrifugal pumps amongst all these thousand of images. I counted zero, but i got tired/bored after a couple of hundred images.

Next do a google image search for "car engine centrifugal oil pump"

Try and find an actual centrifugal oil pump of a car engine. Remarkebly you will find quite a few of the PD pumps listed under the first search here as well. Never mind they are still PD pumps, even though they show up on a search for centrifugal pumps. What do the google boys know.

Next, pick you car manufacturer and google image for your car manufacturer and add engine oil pump. So for instance, Nissan. Search google image for Nissan engine oil pump. you will find PD pumps. Try it for any manufacturer and lets see how many pictures/images there are on the internet of centrifugal oil pumps versus PD pumps.

Never believe what you read on the internet, obviously! But sometimes, only sometimes, I hate to admit, it concurs with my own believes and experiences. Rats, I hate it when the internet does that!

Ignorance is bliss!

Jeroen

[sgiitk]

Let me add my two bits, the oil pumps are in the category of gear pumps. Most high pressure low volume pumps are those. Except there are not true gear pumps either.

[Jeroen]

Originally Posted by sgiitk

Let me add my two bits, the oil pumps are in the category of gear pumps. Most high pressure low volume pumps are those. Except there are not true gear pumps either.

If its a gear pump (and I believe lots of car engine oil pumps are one way or another) its a PD pump!

Thanks

Jeroen

[sgiitk]

Originally Posted by Jeroen

If its a gear pump (and I believe lots of car engine oil pumps are one way or another) its a PD pump!

Exactly. I think most pumps excluding centrifugal pumps are positive displacement. The oil pump basically has some lobes which are powered, and there is an idler which has one lobe more or less.

[khoj]

There is no need to take a statement made w.r.t. to a specific comment and apply it universally to an entire post. I still stand by what I said on the pd pumps performance vis a vis viscosity change.

Similarly the attempt to relate my general comment on existence of reciprocating type pd pumps to their perceived usage w.r.t. cars is indeed amusingly silly.

As for type of pumps used in the cars, I have already said that it is "my understanding" never claimed to be a know all like some others. If pd or some other type of pump is used, fine so be it.

Trolling the internet and wikipedia etc etc is not my cup of tea. One does not know how much of the information is genuine and how much is coming from an armchair expert. The very reason I posted here was to find out what type of pumps are being used in vehicles. However it seems the focus is on trivialising rather than healthy discussion. So in order to seek a definitive reply and being stuck with a bricks and mortar kind of thinking, I contacted the local MSM and the General Manager there will be sending in a scanned image of the type of PD pump that is being used now a days by Maruti.

Meanwhile outside of a car's bonnet the World moves on. Industrial production floors are replete with self priming centrifugals, that too without the help of any external priming aides and I am not talking about submerged pumps either.

Dozens of pump overhauls later if you feel cavitation is a minor issue compared to frothing then obviously you have not seen a PD pump cavitate. When I said it is like a bomb going off I meant it literally. A cavitating PD pump such as a twin/multi screw, especially a gear pump can not only self destruct (in a matter of minutes) but also take down a fair amount of plumbing with it. The foaming as you called it is destructive for the pumpage rather than the pump. Frothing still happens but now a days these episodes are less frequent compared to how often one sees cavitation. This because more often than not the effects of changes in viscosity on a pd pump's performance are ignored amongst other overlooked criterion. Again before this is generally applied to vehicles, I am stating this w.r.t. industrial applications.

Originally Posted by Jeroen

Be my guest, but the evidence to the contrary is utterly overwhelming. Check out Wikipedia, or google images for car engine oil pump and you see you are completely wrong with your centrifugal pumps for car engines. Also, please explain how you will go about them not priming themselves and how to solve that in your typical car engine application. I won't be holding my breath.



Correct it is a PD pump, often mistaken for a centrifugal pump. Sure there are reciprocating PD pumps out there. I've designed, commissioned them and overhauled them many a times. But reciprocating PD pumps as oil pump on a car engine, I don't think I have come across.



See the above, trust me google images of car engine oil pump and you will find hundreds if not thousands of PD pumps, not centrifugal ones.




No its not, cavitation is a very different phenomena, although it does also start with very local low pressure areas, releasing gasses that subsequently implode on the pressure building up as the gas bubbles move along the surface of the impeller/propellor whatever. it can happen on ship propellors, but also on the impellers of for instance centrifugal pumps. It shows as pitting on the impeller/propellor and can destroy it completely. However, it doesn't necessarily impact the normal operation of the pump. That is up to the moment where the impeller is really damaged and bits begin to fall off. So its a real concern to designers. I have overhauled dozens and dozens of pumps and nearly always the impellers of centrifugal pumps had more or less evidence of cavitation. I have seen impellers more than half eaten away by cavitation. Much to my surprise these pumps were working fine. With sufficient pressure and flow. Which might indicate they were heavily over dimensioned in the first place.

What I described earlier is simple foaming of the oil. Much more destructive, if you are not careful as you loose all oil pressure immediately. Whereas cavitation is really an occurrence on a micro level at certain parts of the impeller/propellor, foaming occurs across a large part of the impeller/propellor/worm whatever. Its' best compared by sticking a mixer into a think viscous fluid and see what happens. It will start foaming. Once it starts foaming there is nothing you can do. You need to shut down the engine immediately as the oil pump will simply not work anymore. Then you might have to wait for hours, if not days for the foam to settle and turn back into normal regular oil. Its all down to viscosity/temperature and how fast the pump turns etc. So the only thing you can do to prevent is to heat the oil. So we installed heaters in our cranes on the hydraulic reservoir. We kept blankets wrapped around reservoirs and pumps etc.

You need to be particularly careful after maintenance if you have drained the complete circuit and start refilling it. PD pumps are self priming, but if the oil is to thick, it won't fill the pump quickly enough and this might happen. I've had it happen to me a number of times.




You're telling me. I know of people who fool heartily, against overwhelming evidence, insist on their own stories/opinion without even showing their own data to substantiate their claim. For instance, they would say, most car engine have centrifugal oil pumps, but fail to substantiate their claim. How silly is that?



I completely agree with you. Just so everybody understands, gear and vane pumps are PD pumps. On car engines, the fast majority uses some sort of PD pump. I have seen centrifugal pumps being used on engines as I stated earlier, but not on car engines.

The viscosity point you bring up is true and as I mentioned before another real short fall is their inability of self priming.

Jeroen

[bullrun87]

Originally Posted by khoj

I still stand by what I said on the pd pumps performance vis a vis viscosity change.

Similarly the attempt to relate my general comment on existence of reciprocating type pd pumps to their perceived usage w.r.t. cars is indeed amusingly silly.

As for type of pumps used in the cars, I have already said that it is "my understanding" never claimed to be a know all like some others. If pd or some other type of pump is used, fine so be it.

I contacted the local MSM and the General Manager there will be sending in a scanned image of the type of PD pump that is being used now a days by Maruti.

Meanwhile outside of a car's bonnet the World moves on. Industrial production floors are replete with self priming centrifugals, that too without the help of any external priming aides and I am not talking about submerged pumps either.
.

So what did maruti's GM say? Do all maruti's use the same type of PD pump?
In my experience too cavitation is a far bigger issue leading to disastrous failure and downtime than any frothing concerns. But I guess frothing would depend largely on the fluids being pumped. But I would like to point out that centrifugals are much more reliable (and usually cheaper) and hence the preferred types of pump in most applications. In general PD's whether rotary or reciprocating are used only when centrifugals can not be used to do that job. PD's in industry will be used mostly in high head, low flow applications or when fluid is viscous and pumping a viscous fluid with a centrifugal is a huge waste of energy .