Cold-Blooded Engine it seems
01-05-2013, 07:57 PM
#16
Race Director
Oil takes longer to warm up so that's the determining factor. It should be at normal operating temperature, which means at least 190-200 degrees F. At that point, water temp will already have reached "normal", also at around 200 degrees. Max numbers may vary slightly with ambient temperature combined with hard driving but your oil should always be at the minimum 190-200 mark before high revs.
01-05-2013, 09:35 PM
#18
Back in 1963 I graduated from college and bought a new 1963 340hp Corvette. Since I was designing Temp Controls a few years later I put a thermocouple in the oil drain plug. So I had oil temp meter in the car. Even though the Vett only had 5 quarts of oil the relationship between water temp warm up and oil temp is exactly what I see now. It is related to ambient temp but always lags water by quite a lot.
01-05-2013, 10:47 PM
#19
Burning Brakes
Back in 1963 I graduated from college and bought a new 1963 340hp Corvette. Since I was designing Temp Controls a few years later I put a thermocouple in the oil drain plug. So I had oil temp meter in the car. Even though the Vett only had 5 quarts of oil the relationship between water temp warm up and oil temp is exactly what I see now. It is related to ambient temp but always lags water by quite a lot.
01-06-2013, 05:00 AM
#20
Rennlist Member
Thread Starter
Join Date: Dec 2009
Location: Southern California
Posts: 1,429
Likes: 0
Received 15 Likes
on
15 Posts
Neither my 997.2 S or my Cayenne V8 (which has the same "info screen" bar graph options for engine temp etc. that Gary refers to on his 991) are anywhere close to full operating oil temperature in 6 miles, especially this time of year. I haven't done a timed check but off the top of my head I'd estimate it takes twice as long to reach 200-210 on the oil temp gauge versus the water temp gauge.
Interesting topic, Gary. I'll pay more attention to the exact mileage next time I drive my cars.
Interesting topic, Gary. I'll pay more attention to the exact mileage next time I drive my cars.
Once the water temp reachs its stability target, the oil temp starts rising abruptly. It rises 15° to 20° F for each mile after that. Since the engine workload hasn't increased, it's best to think of that as 15-20°F per minute instead. Finally, the oil reaches something around the same 200°F about the time my attention was needed elsewhere so I didn't spot where it stopped rising. From previous observations, I'd say it stopped rising around 185-190°F and stayed there until I began asking more of the engine. Thereafter, the number of degrees of oil temp above 190° seems to be proportional to how hard I'm working the engine, with a max of about 225°F on a warm day running close to maximum power for several miles. (viz track conditions.)
I didn't have occasion to explore the issue of the oil cooler that engages with sport mode.
Obviously, Porsche have done something that intentionally moves the heat into the coolant preferentially until that comes up to the temperature that other subsystems are designed to expect. Very interesting.
Incidentally, with the small size and relatively low cost of temp sensors I wouldn't put too much attention on placement of the temp sensors. I can't confirm their competence, but I presume that Porsche chose placements that give a result that is representative and most consistently useful for evaluating the engine's condition. I certainly would, so I grant them the same foresight.
Gary
01-06-2013, 05:58 AM
#21
Nordschleife Master
doesn't coolant warm much faster in every car ever made? when i first bought a sports car i was always taught to watch the oil temp and not the water temp because the water heats up faster but the oil temp is what tells you when the engine is actually warmed up and ready.
driving today at 50* my coolant temp hit 180 in 3-4 minutes in the atom, and oil temp didn't reach operating temps for over 10 minutes.
driving today at 50* my coolant temp hit 180 in 3-4 minutes in the atom, and oil temp didn't reach operating temps for over 10 minutes.
01-06-2013, 08:15 AM
#22
Race Car
I've had other things on my mind, so no time to think about causes, but I do have more data. I observed more closely next time and noticed something that is almost certainly an effect of computer control. The oil temp drifts gradually higher, from 48° F in my moderate ambient, to about 70°F after six miles. At that point, I'm on the freeway about a mile south of the on-ramp. The water temp has been climbing sharply all that time until it reaches 200°F, which is the stabilized target it never exceeds unless conditions are approaching unmanageable.
Once the water temp reachs its stability target, the oil temp starts rising abruptly. It rises 15° to 20° F for each mile after that. Since the engine workload hasn't increased, it's best to think of that as 15-20°F per minute instead. Finally, the oil reaches something around the same 200°F about the time my attention was needed elsewhere so I didn't spot where it stopped rising. From previous observations, I'd say it stopped rising around 185-190°F and stayed there until I began asking more of the engine. Thereafter, the number of degrees of oil temp above 190° seems to be proportional to how hard I'm working the engine, with a max of about 225°F on a warm day running close to maximum power for several miles. (viz track conditions.)
I didn't have occasion to explore the issue of the oil cooler that engages with sport mode.
Obviously, Porsche have done something that intentionally moves the heat into the coolant preferentially until that comes up to the temperature that other subsystems are designed to expect. Very interesting.
Incidentally, with the small size and relatively low cost of temp sensors I wouldn't put too much attention on placement of the temp sensors. I can't confirm their competence, but I presume that Porsche chose placements that give a result that is representative and most consistently useful for evaluating the engine's condition. I certainly would, so I grant them the same foresight.
Gary
Once the water temp reachs its stability target, the oil temp starts rising abruptly. It rises 15° to 20° F for each mile after that. Since the engine workload hasn't increased, it's best to think of that as 15-20°F per minute instead. Finally, the oil reaches something around the same 200°F about the time my attention was needed elsewhere so I didn't spot where it stopped rising. From previous observations, I'd say it stopped rising around 185-190°F and stayed there until I began asking more of the engine. Thereafter, the number of degrees of oil temp above 190° seems to be proportional to how hard I'm working the engine, with a max of about 225°F on a warm day running close to maximum power for several miles. (viz track conditions.)
I didn't have occasion to explore the issue of the oil cooler that engages with sport mode.
Obviously, Porsche have done something that intentionally moves the heat into the coolant preferentially until that comes up to the temperature that other subsystems are designed to expect. Very interesting.
Incidentally, with the small size and relatively low cost of temp sensors I wouldn't put too much attention on placement of the temp sensors. I can't confirm their competence, but I presume that Porsche chose placements that give a result that is representative and most consistently useful for evaluating the engine's condition. I certainly would, so I grant them the same foresight.
Gary
Last edited by chuckbdc; 01-06-2013 at 03:57 PM.
01-06-2013, 11:17 AM
#23
With respect to auto engines, and in the absence of CHT probes & gauge, utilizing oil temp for the purpose makes sense to me.
Ken
01-06-2013, 05:45 PM
#24
Rennlist Member
Thread Starter
Join Date: Dec 2009
Location: Southern California
Posts: 1,429
Likes: 0
Received 15 Likes
on
15 Posts
In my past experience of operating large, high-HP radial engines, cylinder head temps (CHTs) were always used to indicate the point at which the engine was ready to go. In the T-6, I wouldn't even taxi until CHTs were 200+.
With respect to auto engines, and in the absence of CHT probes & gauge, utilizing oil temp for the purpose makes sense to me.
Ken
With respect to auto engines, and in the absence of CHT probes & gauge, utilizing oil temp for the purpose makes sense to me.
Ken
Just curious, did Porsche include a cylinder-head-temperature gauge in the early air-cooled models?
Gary
01-06-2013, 07:36 PM
#25
Race Car
Ken's hit on the real issue: temperature in the hardest working parts of the engine is what tells us whether they are ready to accept the rapid injection of more heat that comes from high power operation. Checking the temp of the working fluids at various points is a way to infer those temps we used to measure directly in aircraft engines.
Just curious, did Porsche include a cylinder-head-temperature gauge in the early air-cooled models?
Gary
Just curious, did Porsche include a cylinder-head-temperature gauge in the early air-cooled models?
Gary
PS I did a cruise in normal and sport modes and can verify that going to sport lowers the oil temp. So clearly the oil is getting routed through a cooler in sport mode.
01-06-2013, 10:44 PM
#26
Interesting I never drive my car in normal always sport. In fact I was considering a hack that would put it in sport mode on startup. When I wake the beast up in the spring I'll have to try normal mode to see this effect.
01-07-2013, 01:52 AM
#27
I observed more closely next time and noticed something that is almost certainly an effect of computer control. The oil temp drifts gradually higher, from 48° F in my moderate ambient, to about 70°F after six miles. At that point, I'm on the freeway about a mile south of the on-ramp. The water temp has been climbing sharply all that time until it reaches 200°F, which is the stabilized target it never exceeds unless conditions are approaching unmanageable.
Once the water temp reachs its stability target, the oil temp starts rising abruptly. It rises 15° to 20° F for each mile after that. Since the engine workload hasn't increased, it's best to think of that as 15-20°F per minute instead. Finally, the oil reaches something around the same 200°F about the time my attention was needed elsewhere so I didn't spot where it stopped rising. From previous observations, I'd say it stopped rising around 185-190°F and stayed there until I began asking more of the engine. Thereafter, the number of degrees of oil temp above 190° seems to be proportional to how hard I'm working the engine, with a max of about 225°F on a warm day running close to maximum power for several miles.
Once the water temp reachs its stability target, the oil temp starts rising abruptly. It rises 15° to 20° F for each mile after that. Since the engine workload hasn't increased, it's best to think of that as 15-20°F per minute instead. Finally, the oil reaches something around the same 200°F about the time my attention was needed elsewhere so I didn't spot where it stopped rising. From previous observations, I'd say it stopped rising around 185-190°F and stayed there until I began asking more of the engine. Thereafter, the number of degrees of oil temp above 190° seems to be proportional to how hard I'm working the engine, with a max of about 225°F on a warm day running close to maximum power for several miles.
Virtually all the heat an engine makes is combustion waste energy. The vast majority of coolant flow goes to dissipating this heat from the cylinder heads. (The real reason by the way Porsche went to water cooling, they couldn't continue designing powerful, efficient, low emissions engines within the design limitations imposed by air cooling the heads.) So you start the car and right away combustion is heating the heads and the coolant in the heads.
Not so much the oil though. Because, while coolant is channeled to dissipate heat, oil is only pumped where its needed for lubrication- and as its needed for lubrication all the time, its pumped all the time. Coolant, meanwhile, is controlled by temperature. Very little flows below a certain point, while maximum flow is only attained under conditions of high ambient temp and full engine load. There is in other words a great deal of coolant overhead capacity. The distinction here perfectly explains the varying temps, with no computer and just one rheostat.
There is maybe one detail to fill in, just to make everything crystal clear: the reason oil temp seems to rise faster once water temp has stabilized.
Remember the coolant overhead capacity? Once 200F is reached, the reason it maintains steady at 200F is not that the engine heat output is steady, but that coolant flow is able to increase by whatever amount necessary to hold 200F. Excess heat however is also being conducted away via pistons, con rods and crank- none of which are water cooled, all of which are now rapidly heating the oil.
So, at this point the engine is warmed up- as far as Porsche is concerned anyway, or they would have chosen some higher water temp set point. QED. But we're continuing to drive and while the coolant flow is free to increase by whatever amount necessary to maintain 200F, the oil flow is not, and so naturally enough it starts getting hot even faster- at least that is until it begins to approach whatever temp equilibrates with load, ambient temp and, apparently, Sport setting.
01-07-2013, 04:25 AM
#28
Rennlist Member
Thread Starter
Join Date: Dec 2009
Location: Southern California
Posts: 1,429
Likes: 0
Received 15 Likes
on
15 Posts
There's plenty of computer controlled stuff on these cars, but no reason to think this "almost certainly" is one of them. Its easily explained by the action of the same old ordinary coolant rheostat on virtually any water cooled car on the road today.
Virtually all the heat an engine makes is combustion waste energy. The vast majority of coolant flow goes to dissipating this heat from the cylinder heads. (The real reason by the way Porsche went to water cooling, they couldn't continue designing powerful, efficient, low emissions engines within the design limitations imposed by air cooling the heads.) So you start the car and right away combustion is heating the heads and the coolant in the heads.
Not so much the oil though. Because, while coolant is channeled to dissipate heat, oil is only pumped where its needed for lubrication- and as its needed for lubrication all the time, its pumped all the time. Coolant, meanwhile, is controlled by temperature. Very little flows below a certain point, while maximum flow is only attained under conditions of high ambient temp and full engine load. There is in other words a great deal of coolant overhead capacity. The distinction here perfectly explains the varying temps, with no computer and just one rheostat.
There is maybe one detail to fill in, just to make everything crystal clear: the reason oil temp seems to rise faster once water temp has stabilized.
Remember the coolant overhead capacity? Once 200F is reached, the reason it maintains steady at 200F is not that the engine heat output is steady, but that coolant flow is able to increase by whatever amount necessary to hold 200F. Excess heat however is also being conducted away via pistons, con rods and crank- none of which are water cooled, all of which are now rapidly heating the oil.
So, at this point the engine is warmed up- as far as Porsche is concerned anyway, or they would have chosen some higher water temp set point. QED. But we're continuing to drive and while the coolant flow is free to increase by whatever amount necessary to maintain 200F, the oil flow is not, and so naturally enough it starts getting hot even faster- at least that is until it begins to approach whatever temp equilibrates with load, ambient temp and, apparently, Sport setting.
Virtually all the heat an engine makes is combustion waste energy. The vast majority of coolant flow goes to dissipating this heat from the cylinder heads. (The real reason by the way Porsche went to water cooling, they couldn't continue designing powerful, efficient, low emissions engines within the design limitations imposed by air cooling the heads.) So you start the car and right away combustion is heating the heads and the coolant in the heads.
Not so much the oil though. Because, while coolant is channeled to dissipate heat, oil is only pumped where its needed for lubrication- and as its needed for lubrication all the time, its pumped all the time. Coolant, meanwhile, is controlled by temperature. Very little flows below a certain point, while maximum flow is only attained under conditions of high ambient temp and full engine load. There is in other words a great deal of coolant overhead capacity. The distinction here perfectly explains the varying temps, with no computer and just one rheostat.
There is maybe one detail to fill in, just to make everything crystal clear: the reason oil temp seems to rise faster once water temp has stabilized.
Remember the coolant overhead capacity? Once 200F is reached, the reason it maintains steady at 200F is not that the engine heat output is steady, but that coolant flow is able to increase by whatever amount necessary to hold 200F. Excess heat however is also being conducted away via pistons, con rods and crank- none of which are water cooled, all of which are now rapidly heating the oil.
So, at this point the engine is warmed up- as far as Porsche is concerned anyway, or they would have chosen some higher water temp set point. QED. But we're continuing to drive and while the coolant flow is free to increase by whatever amount necessary to maintain 200F, the oil flow is not, and so naturally enough it starts getting hot even faster- at least that is until it begins to approach whatever temp equilibrates with load, ambient temp and, apparently, Sport setting.
Gary
01-07-2013, 08:20 AM
#29
Race Car
There's plenty of computer controlled stuff on these cars, but no reason to think this "almost certainly" is one of them. Its easily explained by the action of the same old ordinary coolant rheostat on virtually any water cooled car on the road today.
Virtually all the heat an engine makes is combustion waste energy. The vast majority of coolant flow goes to dissipating this heat from the cylinder heads. (The real reason by the way Porsche went to water cooling, they couldn't continue designing powerful, efficient, low emissions engines within the design limitations imposed by air cooling the heads.) So you start the car and right away combustion is heating the heads and the coolant in the heads.
Not so much the oil though. Because, while coolant is channeled to dissipate heat, oil is only pumped where its needed for lubrication- and as its needed for lubrication all the time, its pumped all the time. Coolant, meanwhile, is controlled by temperature. Very little flows below a certain point, while maximum flow is only attained under conditions of high ambient temp and full engine load. There is in other words a great deal of coolant overhead capacity. The distinction here perfectly explains the varying temps, with no computer and just one rheostat.
There is maybe one detail to fill in, just to make everything crystal clear: the reason oil temp seems to rise faster once water temp has stabilized.
Remember the coolant overhead capacity? Once 200F is reached, the reason it maintains steady at 200F is not that the engine heat output is steady, but that coolant flow is able to increase by whatever amount necessary to hold 200F. Excess heat however is also being conducted away via pistons, con rods and crank- none of which are water cooled, all of which are now rapidly heating the oil.
So, at this point the engine is warmed up- as far as Porsche is concerned anyway, or they would have chosen some higher water temp set point. QED. But we're continuing to drive and while the coolant flow is free to increase by whatever amount necessary to maintain 200F, the oil flow is not, and so naturally enough it starts getting hot even faster- at least that is until it begins to approach whatever temp equilibrates with load, ambient temp and, apparently, Sport setting.
Virtually all the heat an engine makes is combustion waste energy. The vast majority of coolant flow goes to dissipating this heat from the cylinder heads. (The real reason by the way Porsche went to water cooling, they couldn't continue designing powerful, efficient, low emissions engines within the design limitations imposed by air cooling the heads.) So you start the car and right away combustion is heating the heads and the coolant in the heads.
Not so much the oil though. Because, while coolant is channeled to dissipate heat, oil is only pumped where its needed for lubrication- and as its needed for lubrication all the time, its pumped all the time. Coolant, meanwhile, is controlled by temperature. Very little flows below a certain point, while maximum flow is only attained under conditions of high ambient temp and full engine load. There is in other words a great deal of coolant overhead capacity. The distinction here perfectly explains the varying temps, with no computer and just one rheostat.
There is maybe one detail to fill in, just to make everything crystal clear: the reason oil temp seems to rise faster once water temp has stabilized.
Remember the coolant overhead capacity? Once 200F is reached, the reason it maintains steady at 200F is not that the engine heat output is steady, but that coolant flow is able to increase by whatever amount necessary to hold 200F. Excess heat however is also being conducted away via pistons, con rods and crank- none of which are water cooled, all of which are now rapidly heating the oil.
So, at this point the engine is warmed up- as far as Porsche is concerned anyway, or they would have chosen some higher water temp set point. QED. But we're continuing to drive and while the coolant flow is free to increase by whatever amount necessary to maintain 200F, the oil flow is not, and so naturally enough it starts getting hot even faster- at least that is until it begins to approach whatever temp equilibrates with load, ambient temp and, apparently, Sport setting.
A bit more after a chat with a Porsche service tech: there are 9 computer controlled modes for routing water and oil for thermal management on the 991, mostly but not all related to emisions control.
Last edited by chuckbdc; 01-07-2013 at 10:52 AM.
01-07-2013, 01:14 PM
#30
Oh, I'm sure its much more elaborate than one simple rheostat. My point was that I'd expect to see pretty much the same temp rise changes either way. More dramatically of course with 9 modes but different only in degree not the general trend.
Back when I was reading everything they had on-line I could have sworn somewhere it said they use 7 different electric oil pumps. But last night, only found one reference to thermal management that mentioned "an" electric oil pump. I'm sure they must use more than just one.
Back when I was reading everything they had on-line I could have sworn somewhere it said they use 7 different electric oil pumps. But last night, only found one reference to thermal management that mentioned "an" electric oil pump. I'm sure they must use more than just one.