Why so much oil? Water-cooled v. Air-cooled
09-08-2007, 10:46 AM
#1
Racer
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Why so much oil? Water-cooled v. Air-cooled
The M96 engines in the 996 and Boxster are water-cooled. The idea being that the coolent is circulated through the block, thus helping cool the cylinders and the heat is eventually released (in part) via the radiators. The Boxster (and I assume the 996) still uses over 9 quarts of oil.
The older 911's (993 and earlier) are air-cooled. There is no radiator in this design and most heat is simply dissipated through the exhaust. In addition, the cylinders have metal “fins” around them that aid in the cooling process. Rather than circulating coolant through the block, oil aids in dispersing heat and is circulated through an oil cooler (similar, I guess, in theory to a radiator). As a result of this design, these older 911’s need to use more oil - I think my SC used in the neighborhood of 11 quarts of oil.
Now, here comes my question, assuming my basic understanding above is true, why do the M96 water-cooled engines require so much oil?
With the M96 there is nearly as much as the air-cooled cars and significantly more than most other water-cooled cars that I’ve had – which only require 5-6 quarts of oil.
The older 911's (993 and earlier) are air-cooled. There is no radiator in this design and most heat is simply dissipated through the exhaust. In addition, the cylinders have metal “fins” around them that aid in the cooling process. Rather than circulating coolant through the block, oil aids in dispersing heat and is circulated through an oil cooler (similar, I guess, in theory to a radiator). As a result of this design, these older 911’s need to use more oil - I think my SC used in the neighborhood of 11 quarts of oil.
Now, here comes my question, assuming my basic understanding above is true, why do the M96 water-cooled engines require so much oil?
With the M96 there is nearly as much as the air-cooled cars and significantly more than most other water-cooled cars that I’ve had – which only require 5-6 quarts of oil.
09-08-2007, 01:57 PM
#3
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09-08-2007, 04:21 PM
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Isn't it a 4 cylinder? and would you really try to drive it like a Boxster? As a guess i'd say you'd want the extra cooling driving a roadster than in a "familyish" type vehicle. I assume the requirements are less.
But then again, what do i know. I drive so slow that even the HWFMR folks look fast. :P
But then again, what do i know. I drive so slow that even the HWFMR folks look fast. :P
Last edited by Sputter; 09-08-2007 at 04:40 PM.
09-08-2007, 04:56 PM
#5
Racer
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Isn't it a 4 cylinder? and would you really try to drive it like a Boxster? As a guess i'd say you'd want the extra cooling driving a roadster than in a "familyish" type vehicle. I assume the requirements are less.
But then again, what do i know. I drive so slow that even the HWFMR folks look fast. :P
But then again, what do i know. I drive so slow that even the HWFMR folks look fast. :P
http://www.roadandtrack.com/article....article_id=592
Whether it's a roadster or a sedan doesn't have anything to do with it. The only cooling issues where that matters are in the the pasenger compartment - top up v. top down.
Last edited by J-RAD; 09-08-2007 at 05:32 PM.
09-08-2007, 07:26 PM
#6
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Subscribed...I'm kinda curious myself. I'm sure the quantity is because these cars are (partial) dry sump systems, so a question to tie into yours is why go with the dry sump system (even partial) if the cars are water cooled?
09-08-2007, 08:10 PM
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Evidently you're not familiar with the STi. Here's some info..
http://www.roadandtrack.com/article....article_id=592
Whether it's a roadster or a sedan doesn't have anything to do with it. The only cooling issues where that matters are in the the pasenger compartment - top up v. top down.
http://www.roadandtrack.com/article....article_id=592
Whether it's a roadster or a sedan doesn't have anything to do with it. The only cooling issues where that matters are in the the pasenger compartment - top up v. top down.
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09-08-2007, 09:00 PM
#8
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more oil in the engine gives the oil more time to cool down before it is cycled back through the engine. Each oil molecule has to "work" less. also the oil service interval is now 15k. I am sure if you only had 6 quarts the oil would wear out before that many miles were covered. (I still change my oil 2x per year) 5-7k
09-09-2007, 09:40 AM
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Dry sump = smaller oil pan = lower center of gravity for the motor = better handling.
Also, doesn't the boxster have an external oil cooler? If so, need some extra oil simply to circulate to and from the cooler, which is no doubt mounted in the front of the car.
Water cooling the engine doesn't necessarily mean less oil, just means you've added water to the equation to aid in cooling.
Also, doesn't the boxster have an external oil cooler? If so, need some extra oil simply to circulate to and from the cooler, which is no doubt mounted in the front of the car.
Water cooling the engine doesn't necessarily mean less oil, just means you've added water to the equation to aid in cooling.
09-09-2007, 09:50 AM
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Yeah the 928 takes 8 litres not sure what that works out to be in the U.S...
its got an oil cooler and radiator. Its allot of oil but i guess thats cleaner oil
running around and as stated the oil would stay cooler.
Takes a while to get to optimum operating temperatures.
Sam
its got an oil cooler and radiator. Its allot of oil but i guess thats cleaner oil
running around and as stated the oil would stay cooler.
Takes a while to get to optimum operating temperatures.
Sam
09-09-2007, 02:04 PM
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Post your question on http://theoildrop.server101.com/forums/ubbthreads.php and you will appreciate the crankcase capacity!
09-11-2007, 06:31 PM
#12
Race Director
It is a big engine not in displacement but in size. There are longer and more oil ...
The M96 engines in the 996 and Boxster are water-cooled. The idea being that the coolent is circulated through the block, thus helping cool the cylinders and the heat is eventually released (in part) via the radiators. The Boxster (and I assume the 996) still uses over 9 quarts of oil.
The older 911's (993 and earlier) are air-cooled. There is no radiator in this design and most heat is simply dissipated through the exhaust. In addition, the cylinders have metal “fins” around them that aid in the cooling process. Rather than circulating coolant through the block, oil aids in dispersing heat and is circulated through an oil cooler (similar, I guess, in theory to a radiator). As a result of this design, these older 911’s need to use more oil - I think my SC used in the neighborhood of 11 quarts of oil.
Now, here comes my question, assuming my basic understanding above is true, why do the M96 water-cooled engines require so much oil?
With the M96 there is nearly as much as the air-cooled cars and significantly more than most other water-cooled cars that I’ve had – which only require 5-6 quarts of oil.
The older 911's (993 and earlier) are air-cooled. There is no radiator in this design and most heat is simply dissipated through the exhaust. In addition, the cylinders have metal “fins” around them that aid in the cooling process. Rather than circulating coolant through the block, oil aids in dispersing heat and is circulated through an oil cooler (similar, I guess, in theory to a radiator). As a result of this design, these older 911’s need to use more oil - I think my SC used in the neighborhood of 11 quarts of oil.
Now, here comes my question, assuming my basic understanding above is true, why do the M96 water-cooled engines require so much oil?
With the M96 there is nearly as much as the air-cooled cars and significantly more than most other water-cooled cars that I’ve had – which only require 5-6 quarts of oil.
Plus all the pistons have oil jets that squirt a considerable amount of oil at the underneath surfaces of the pistons to help keep piston crown temps down and provide good lubrication to the cylinders/pistons/rings/small rod end bearings.
But this causes alot of oil to be in suspension.
Another factor is the horizontal layout with DOHC sees a lot of oil under the camshaft covers -- DOHC require alot of oil to ensure proper lubrication -- and under hard cornering can see some build up of oil that is out of the reach of the oil scavenge pumps. Which brings me to this: And because the Boxster engine does not have a dry sump oiling system and doesn't have the proper number of oil scavenge pumps under the camshaft covers. It really should have 4, 2 per side, one at each end of the camshaft cover.
But it didn't get these. Instead it gets a larger oil supply. Cheaper.
So, the larger amount of oil is to ensure that there is always sufficient defoamed oil so the oil pump never sees anything but defoamed oil.
Sincerely,
Macster.
09-16-2007, 09:38 PM
#13
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Dry sumps 'n things
Hi,
there are a variety of reasons why an engine designer may opt for, or be "forced" to use, a dry sump lubrication system
These range from the need for a larger oil supply than would be possible otherwise to "simple" things like the lateral and longitudinal "G" forces likely to encountered in use, cost, to the overall engine design and its application etc.
The need for more than one oil pump - usually only a supply pump is needed - places special requirements on the lubricant. The scavenge and supply pumps (sometimes up to eight or nine) introduce the real risks of cavitation and foaming caused by air saturation. This can have a very serious negative effect on overall engine durability. If more than one pump is used they may be of different designs/construction
Porsche have for some decades opted for a large oil supply which has enabled long oil change intervals. This has been a design principle and it offers potentially lower servicing costs aligned with managing some of the "issues" mentioned earlier.
Oil coolers that are an integral part of the cooling system (oil to water intercooler) enable the oil to be warmed quickly (oil can trail coolant by 20C or more from a cold warm up) and for it to enter the engine without a great "thermal shock" if thermostatically controlled. Air to oil coolers controlled by a thermostat can be used to "contain" the temperature limits when at elevated temperatures. This has a positive effect on the liquid cooling system's thermal capacity
Approved oils to be used in Porsche engines have very good thermal characteristics up to and beyond 130C. Ideally the Approved lubricants should be kept within a range from about 90C to around 115C. In each case too cold is much worse than containment within the ideal range
The use of a dry sump system can either raise or lower the vehicle's roll centre and not all "storage" containers are mounted remotely from the engine
Both coolant and oil play vital roles in minimising temperature variances within the engine when it reaches its designed "core" operating temperature. A large oil capacity gives the oil time to dissipate more heat when in "bulk holding mode" and enables the regeneration of the temporary shearing "abilities" of the lubricant. As a matter of interest it takes up to five minutes or so for some lubricants to enter and leave the ring pack area! The more viscous the lubricant the longer the "cycle" time!!!
Air cooled engines are usually very well sorted out by the designers in regard to the expected oil temperatures and the rate of oil degradation. Most cooling problems with air cooled engines are NOT oil related - it is usually an air flow issue
Viscous mineral oils do NOT do as good a job as a synthetic oil in the correct viscosity range. This is principally a factor of oil FLOW rather than anything else - the more linear molecular structure of a synthetic lubricant reduces internal friction and speeds the dissipation of heat
Macster - the M96 engine in the Boxster has three oil pumps (two types) and an integral "dry" sump - some of your comments may be unintentionally misleading
Regards
there are a variety of reasons why an engine designer may opt for, or be "forced" to use, a dry sump lubrication system
These range from the need for a larger oil supply than would be possible otherwise to "simple" things like the lateral and longitudinal "G" forces likely to encountered in use, cost, to the overall engine design and its application etc.
The need for more than one oil pump - usually only a supply pump is needed - places special requirements on the lubricant. The scavenge and supply pumps (sometimes up to eight or nine) introduce the real risks of cavitation and foaming caused by air saturation. This can have a very serious negative effect on overall engine durability. If more than one pump is used they may be of different designs/construction
Porsche have for some decades opted for a large oil supply which has enabled long oil change intervals. This has been a design principle and it offers potentially lower servicing costs aligned with managing some of the "issues" mentioned earlier.
Oil coolers that are an integral part of the cooling system (oil to water intercooler) enable the oil to be warmed quickly (oil can trail coolant by 20C or more from a cold warm up) and for it to enter the engine without a great "thermal shock" if thermostatically controlled. Air to oil coolers controlled by a thermostat can be used to "contain" the temperature limits when at elevated temperatures. This has a positive effect on the liquid cooling system's thermal capacity
Approved oils to be used in Porsche engines have very good thermal characteristics up to and beyond 130C. Ideally the Approved lubricants should be kept within a range from about 90C to around 115C. In each case too cold is much worse than containment within the ideal range
The use of a dry sump system can either raise or lower the vehicle's roll centre and not all "storage" containers are mounted remotely from the engine
Both coolant and oil play vital roles in minimising temperature variances within the engine when it reaches its designed "core" operating temperature. A large oil capacity gives the oil time to dissipate more heat when in "bulk holding mode" and enables the regeneration of the temporary shearing "abilities" of the lubricant. As a matter of interest it takes up to five minutes or so for some lubricants to enter and leave the ring pack area! The more viscous the lubricant the longer the "cycle" time!!!
Air cooled engines are usually very well sorted out by the designers in regard to the expected oil temperatures and the rate of oil degradation. Most cooling problems with air cooled engines are NOT oil related - it is usually an air flow issue
Viscous mineral oils do NOT do as good a job as a synthetic oil in the correct viscosity range. This is principally a factor of oil FLOW rather than anything else - the more linear molecular structure of a synthetic lubricant reduces internal friction and speeds the dissipation of heat
Macster - the M96 engine in the Boxster has three oil pumps (two types) and an integral "dry" sump - some of your comments may be unintentionally misleading
Regards
09-17-2007, 02:13 PM
#14
Race Director
The Boxster engine has 1 oil pump that has a scavenge and high...
Integral dry sump is just marketing hooey. It is a wet sump oil system.
I fail to see how my comments could be misleading, unintentional or intentional.
Longer times between oil changes is not due to a larger oil capacity. Many other car makers have been extending the time between oil changes and have not increased the oil capacity of their engines. Even Porsche was IIRC up to 20,000 miles between oil changes and AFAIK the newer Boxster/Carrera engines have the same oil capacity as the older ones for which shorter oil change intervals were specified.
Longer oil change intervals is more marketing hooey. It is done to lower the cost of ownership to make the higher sales prices more attractive, well, more tolerable. Longer oil change intervals has nothing much to do with improved oil, improved engine manufacturing. It does have something to do with the removal of lead from gasoline, but modern engines with the burden of emissions controls in other ways cancels out the absence of lead in modern gasolines.
Sincerely,
Macster.
09-17-2007, 09:16 PM
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It's located on the lower driver side,underneath the throttle body. The base Boxster cooler has it's own smaller design,the Boxster S/996 cooler is almost twice the size.