LAGUNA SECA SCCA RACE Sept 2nd, 2017 this weekend!
09-01-2017, 10:41 PM
#16
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Thread Starter
was on the track today. 100F degrees. FLIPPING way too HOT !!! anyway, i did an experiment again. no bleeding and normal coolant level. it over heated after a few laps. (very close to the light coming on and oil temp over 260) however, still lots of pressure in the system. (not like last years failure). Then, i burped the system and fillled the reservoir to 1" below the top. qualified and temp only went to half way, and was pegged there. near the end, it started to creep up and turned on the second of two fans, and went down to the normal horizontal level. no issues.
race tomorrow 12 noon forcast 100f temps
race tomorrow 12 noon forcast 100f temps
09-04-2017, 01:56 PM
#19
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09-04-2017, 02:04 PM
#20
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The Laguna Seca race was fun until the temps started to climb and the ole 928 started to overheat. Laguna was the highest ever seen by any racer i know. 105F at the track!! oil was highest ive ever seen, going past 280F and water stabilized after being right at the middle area for 5 laps... climbing to just short of the warning light. so, i had to back off and let it cool while losing 2 positions and the 1st place in GT2 ..............but , thought i might have been able to grab them back on a restart near the end of the race , but they through the checker instead of a green 
Not a huge field , but ended up in 2nd in GT2, just loosing to the WC GTS Cayman who i had to point by when i was overheating. 
anyway, it was brutal.. worse than any Thunderhill race too and we have had a few of them over 100F over the years. no place to hide very little shade, and laguna is not a super fast track, so you dont get the high speed air flow that you get at the longer tracks in the heat. anyway, ill never do that again, unless i get a bigger radiator .
(and an oil cooler).
Here is the video. front view cam for the start and restarts, and the last part of the video shows the rear cam starts.
Not a huge field , but ended up in 2nd in GT2, just loosing to the WC GTS Cayman who i had to point by when i was overheating. anyway, it was brutal.. worse than any Thunderhill race too and we have had a few of them over 100F over the years. no place to hide very little shade, and laguna is not a super fast track, so you dont get the high speed air flow that you get at the longer tracks in the heat. anyway, ill never do that again, unless i get a bigger radiator .
(and an oil cooler). Here is the video. front view cam for the start and restarts, and the last part of the video shows the rear cam starts.
09-05-2017, 04:21 AM
#22
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Your 928 is now handling noticeably better than your group competitors or so it seemed to me and more so in the Corkcrew.
Remember if you do not get the heat out of the engine oil it only adds to the heat load on the main cooling system. I take it you run your coolant mix a bit lean possibly with water wetter?
Remember if you do not get the heat out of the engine oil it only adds to the heat load on the main cooling system. I take it you run your coolant mix a bit lean possibly with water wetter?
09-05-2017, 12:09 PM
#23
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Originally Posted by mark kibort
Thanks for coming out Rick and Richard! great to catch up and cool off over lunch!
Mark
Mark
Just helping to support the 928 flag ⛳️ 😁
09-05-2017, 12:20 PM
#24
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Your 928 is now handling noticeably better than your group competitors or so it seemed to me and more so in the Corkcrew.
Remember if you do not get the heat out of the engine oil it only adds to the heat load on the main cooling system. I take it you run your coolant mix a bit lean possibly with water wetter?
Remember if you do not get the heat out of the engine oil it only adds to the heat load on the main cooling system. I take it you run your coolant mix a bit lean possibly with water wetter?
as far as cooling, i think the oil tied to the water was too much for the water, for sure. 280F oil hitting 220F water cant be a good thing!
Richard and i were talking about it at the track. If we can keep the water from boiling, it doesnt form the air pockets which limits flow in the cooling system. im running straight water (with a little coolant 5%), and water wetter, but if i run some coolant (kind-of illegal in racing) i might be able to raise the boiling point
which would keep the water in the normal range and help with the oil temp.
Laguna just doesnt have enough speed as other tracks to keep the coolant temp down when the temps are over 100F. this is the first time we have ever had temps this high in over 20 years! the most we ever see was near 90F and that was no problem at all. just last month, we were 80 and the fans actually turned off mid race...
09-05-2017, 01:51 PM
#25
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Mark,
If your coolant was boiling you would be totally buggered- it would not be air in the system it would be steam and when that forms it will seriously disrupt coolant flow and the rate of heat exchange will drop dramatically- game, set and match type of thing..
That being said you must be pretty close to the boiling point but as long as you do not get there it will be fine. A leaner mix is optimal because water has a greater specific heat capacity compared to the glycol but as you get closer to pure water the boiling point drops and in your case there will be negligible difference between pure water and the mix you use. Thus at 5 psig your boiling point will be about 230F and at 15 psig it will be 250F. To get the pressure up as high as possible you need to keep the air space above the coolant level minimal so that the pressure increases more with thermal expansion of the coolant compressing the air space- worst case scenario is a little vents out of the cap and then you are optimal.
If your coolant was boiling you would be totally buggered- it would not be air in the system it would be steam and when that forms it will seriously disrupt coolant flow and the rate of heat exchange will drop dramatically- game, set and match type of thing..
That being said you must be pretty close to the boiling point but as long as you do not get there it will be fine. A leaner mix is optimal because water has a greater specific heat capacity compared to the glycol but as you get closer to pure water the boiling point drops and in your case there will be negligible difference between pure water and the mix you use. Thus at 5 psig your boiling point will be about 230F and at 15 psig it will be 250F. To get the pressure up as high as possible you need to keep the air space above the coolant level minimal so that the pressure increases more with thermal expansion of the coolant compressing the air space- worst case scenario is a little vents out of the cap and then you are optimal.
09-05-2017, 03:11 PM
#26
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terminology.. yes, i was speaking of boiling and steam. again. we ahve been down this route. proof in the fact that 1/2 gallon was missing and boiled out the overflow. the engine cooled during caution laps and when i came in the pits, the temp was second white line, and oil back to normal racing 250F. but it took a while . hoses were colapsed meaning, steam condensed back to liquid and there was no pressure in the system....
Yes, it was boiling, and yes it was a game over situation when temps got near red and oil started to go ballistic toward 300F. so, just cruised and slowly after 5 miles of near part throttle and lower RPM, temps came down.
prior overheating in practice for the test....... had air in the lines and it did what i expected. started to overheat quickly.. with air in the system. bled it before qualifying.. no issues during hotter conditions during qualifying 2.5 hours later.
the one thing i did ive never did, was make the coolant level very close to the top. i figured worst case, it would just bleed off any excess... but in thinking about it, could that be the issue? instead of compressing the air, there is no compressing to lower boiling point so the water boils??? when there is no air, isnt there still a pressure needed to push water out the overflow that can keep the boiling point up?
another bit of logic was that by using more antifreeze, the boiling point goes up, , so that it doesnt boil and the coolant continues to circulate effectively..event though i was hot, and maybe coolant doesnt work quite as well as gycol, its beter than greatly reduced circulation. again, the difference between this day and a thunderhill day at the same temp outside, is that thunderhill had such higher speeds for much longer periods of time... probably just keeping it under the boiling point.
Yes, it was boiling, and yes it was a game over situation when temps got near red and oil started to go ballistic toward 300F. so, just cruised and slowly after 5 miles of near part throttle and lower RPM, temps came down.
prior overheating in practice for the test....... had air in the lines and it did what i expected. started to overheat quickly.. with air in the system. bled it before qualifying.. no issues during hotter conditions during qualifying 2.5 hours later.
the one thing i did ive never did, was make the coolant level very close to the top. i figured worst case, it would just bleed off any excess... but in thinking about it, could that be the issue? instead of compressing the air, there is no compressing to lower boiling point so the water boils??? when there is no air, isnt there still a pressure needed to push water out the overflow that can keep the boiling point up?
another bit of logic was that by using more antifreeze, the boiling point goes up, , so that it doesnt boil and the coolant continues to circulate effectively..event though i was hot, and maybe coolant doesnt work quite as well as gycol, its beter than greatly reduced circulation. again, the difference between this day and a thunderhill day at the same temp outside, is that thunderhill had such higher speeds for much longer periods of time... probably just keeping it under the boiling point.
Mark,
If your coolant was boiling you would be totally buggered- it would not be air in the system it would be steam and when that forms it will seriously disrupt coolant flow and the rate of heat exchange will drop dramatically- game, set and match type of thing..
That being said you must be pretty close to the boiling point but as long as you do not get there it will be fine. A leaner mix is optimal because water has a greater specific heat capacity compared to the glycol but as you get closer to pure water the boiling point drops and in your case there will be negligible difference between pure water and the mix you use. Thus at 5 psig your boiling point will be about 230F and at 15 psig it will be 250F. To get the pressure up as high as possible you need to keep the air space above the coolant level minimal so that the pressure increases more with thermal expansion of the coolant compressing the air space- worst case scenario is a little vents out of the cap and then you are optimal.
If your coolant was boiling you would be totally buggered- it would not be air in the system it would be steam and when that forms it will seriously disrupt coolant flow and the rate of heat exchange will drop dramatically- game, set and match type of thing..
That being said you must be pretty close to the boiling point but as long as you do not get there it will be fine. A leaner mix is optimal because water has a greater specific heat capacity compared to the glycol but as you get closer to pure water the boiling point drops and in your case there will be negligible difference between pure water and the mix you use. Thus at 5 psig your boiling point will be about 230F and at 15 psig it will be 250F. To get the pressure up as high as possible you need to keep the air space above the coolant level minimal so that the pressure increases more with thermal expansion of the coolant compressing the air space- worst case scenario is a little vents out of the cap and then you are optimal.
09-05-2017, 04:29 PM
#27
Rennlist Member
terminology.. yes, i was speaking of boiling and steam. again. we ahve been down this route. proof in the fact that 1/2 gallon was missing and boiled out the overflow. the engine cooled during caution laps and when i came in the pits, the temp was second white line, and oil back to normal racing 250F. but it took a while . hoses were colapsed meaning, steam condensed back to liquid and there was no pressure in the system....
Yes, it was boiling, and yes it was a game over situation when temps got near red and oil started to go ballistic toward 300F. so, just cruised and slowly after 5 miles of near part throttle and lower RPM, temps came down.
prior overheating in practice for the test....... had air in the lines and it did what i expected. started to overheat quickly.. with air in the system. bled it before qualifying.. no issues during hotter conditions during qualifying 2.5 hours later.
the one thing i did ive never did, was make the coolant level very close to the top. i figured worst case, it would just bleed off any excess... but in thinking about it, could that be the issue? instead of compressing the air, there is no compressing to lower boiling point so the water boils??? when there is no air, isnt there still a pressure needed to push water out the overflow that can keep the boiling point up?
another bit of logic was that by using more antifreeze, the boiling point goes up, , so that it doesnt boil and the coolant continues to circulate effectively..event though i was hot, and maybe coolant doesnt work quite as well as gycol, its beter than greatly reduced circulation. again, the difference between this day and a thunderhill day at the same temp outside, is that thunderhill had such higher speeds for much longer periods of time... probably just keeping it under the boiling point.
Yes, it was boiling, and yes it was a game over situation when temps got near red and oil started to go ballistic toward 300F. so, just cruised and slowly after 5 miles of near part throttle and lower RPM, temps came down.
prior overheating in practice for the test....... had air in the lines and it did what i expected. started to overheat quickly.. with air in the system. bled it before qualifying.. no issues during hotter conditions during qualifying 2.5 hours later.
the one thing i did ive never did, was make the coolant level very close to the top. i figured worst case, it would just bleed off any excess... but in thinking about it, could that be the issue? instead of compressing the air, there is no compressing to lower boiling point so the water boils??? when there is no air, isnt there still a pressure needed to push water out the overflow that can keep the boiling point up?
another bit of logic was that by using more antifreeze, the boiling point goes up, , so that it doesnt boil and the coolant continues to circulate effectively..event though i was hot, and maybe coolant doesnt work quite as well as gycol, its beter than greatly reduced circulation. again, the difference between this day and a thunderhill day at the same temp outside, is that thunderhill had such higher speeds for much longer periods of time... probably just keeping it under the boiling point.
As I can tell you are describing something similar to what happened previously. The information you have presented is not consistent with sound engineering logic. Either your temperature indication readings are wrong or you are not making pressure. Your cooling system cannot possibly boil up until the coolant temperature hits 250C if the system is holding pressure up to 15 psig- no need for debate on this.
Your description of events suggests to me that when your motor is hot it can only hold pressure up to about 5 psig as this is the equilibrium point corresponding to a water temperature of 220F. You stated that at this point the oil temperature soared- quite logical as the coolant has started boiling and thus the heat transfer coefficient has gone to rat sh*t , heat is staying in the motor so the oil temp goes up. However the indicated coolant temperature stays the same because it is now boiling. You slow down and reduce the heat load the system comes back to equilibrium. Now the question is do you know how and where the coolant is getting out? Do you know for a fact that the pressure cap is lifting or are you assuming that is the case? Either way the cooling system pressure cannot be higher than 5 psig. So the question that logic says needs to be answered is where is the pressure escaping from? Maybe the expansion tank has a leak?
Once the system has heated up and has reached equilibrium the system pressure should not relax until the system has cooled down.
If you have not done so already you need to carry out a static pressure test at 15 psig and record the pressure versus time. If everything is working OK it should hold that pressure for a long time with a very slow rate of decay. Whether this test can replicate what happens when the motor is hot remains to be seen but it is about as close as one can get. If the system holds 15 psig then we need to scratch our heads a bit more.
09-05-2017, 05:05 PM
#28
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Thread Starter
yes, this can happen, check this engineering logic . see if you agree.
if the water boils and pushes out 1/2 gallon of water, and steam has replaced the water in the cooling system, the level of the overflow is full and water is being pushed out at 15psi. as the steam condenses, or gas has moved out of the system, the level goes down showing normal level. (not the overfill i started with). the hoses are flat... temps are still over mid white line but below boiling point at no pressure.
the same thing happened with air in the sytem in the pior day practice. it was high pressure for about 45min before i could open the vent with no air escaping. it takes a long time for the pressure to go down normally.
yes, temps rose to 250 water to boil it the temps were just before the red. the red didnt go on, so just before. ( i dont know that temp limit)
i did this in practice, but backed off so no coolant was lost and started with a normal (half way line ) fill of water. pressure was near max. lines were hard as rocks. same thing after a fill to higher level for qualifying 105 track temp too. no issues, but it was a short session. fulll pressure, and it lasted 30 to 45min before it was softer. 1 hours before i could open and not have any air escape. why do you say, im limited to 220F or 5psi.. the cap is tested and the system has No leaks to 15psi . lasted perfectly for over an hour.
you are forgetting that if the cooliing system water boiled, pushed out 1/2 gallon, then was cooled.. the air cant return from the cap its a one way valve, so the condencing steam and the now, non boiling coolant, find a situation where there is no pressure and under 210F water temps, as was achieved during the cool down laps. no smoke from the car either so its not being pushed into the cylinders. rear view camera of entire race proves that.
again, its why im asking. im puzzeled and only coming up with theories. the cap doesnt leak and holds pressure. the system pressure holds for an hour normally. ill go drive it right now and check again.....
EDIT: forgot to mention that i did tests.. with Richard there too. fans kicked on by the radiator temp sensor, matching the temp gauge temp points where fans kick on. (that sensor is in the lower radiator driver side that switchs the fans on) hoses still had no pressure
if the water boils and pushes out 1/2 gallon of water, and steam has replaced the water in the cooling system, the level of the overflow is full and water is being pushed out at 15psi. as the steam condenses, or gas has moved out of the system, the level goes down showing normal level. (not the overfill i started with). the hoses are flat... temps are still over mid white line but below boiling point at no pressure.
the same thing happened with air in the sytem in the pior day practice. it was high pressure for about 45min before i could open the vent with no air escaping. it takes a long time for the pressure to go down normally.
yes, temps rose to 250 water to boil it the temps were just before the red. the red didnt go on, so just before. ( i dont know that temp limit)
i did this in practice, but backed off so no coolant was lost and started with a normal (half way line ) fill of water. pressure was near max. lines were hard as rocks. same thing after a fill to higher level for qualifying 105 track temp too. no issues, but it was a short session. fulll pressure, and it lasted 30 to 45min before it was softer. 1 hours before i could open and not have any air escape. why do you say, im limited to 220F or 5psi.. the cap is tested and the system has No leaks to 15psi . lasted perfectly for over an hour.
you are forgetting that if the cooliing system water boiled, pushed out 1/2 gallon, then was cooled.. the air cant return from the cap its a one way valve, so the condencing steam and the now, non boiling coolant, find a situation where there is no pressure and under 210F water temps, as was achieved during the cool down laps. no smoke from the car either so its not being pushed into the cylinders. rear view camera of entire race proves that.
again, its why im asking. im puzzeled and only coming up with theories. the cap doesnt leak and holds pressure. the system pressure holds for an hour normally. ill go drive it right now and check again.....
EDIT: forgot to mention that i did tests.. with Richard there too. fans kicked on by the radiator temp sensor, matching the temp gauge temp points where fans kick on. (that sensor is in the lower radiator driver side that switchs the fans on) hoses still had no pressure
Mark,
As I can tell you are describing something similar to what happened previously. The information you have presented is not consistent with sound engineering logic. Either your temperature indication readings are wrong or you are not making pressure. Your cooling system cannot possibly boil up until the coolant temperature hits 250C if the system is holding pressure up to 15 psig- no need for debate on this.
Your description of events suggests to me that when your motor is hot it can only hold pressure up to about 5 psig as this is the equilibrium point corresponding to a water temperature of 220F. You stated that at this point the oil temperature soared- quite logical as the coolant has started boiling and thus the heat transfer coefficient has gone to rat sh*t , heat is staying in the motor so the oil temp goes up. However the indicated coolant temperature stays the same because it is now boiling. You slow down and reduce the heat load the system comes back to equilibrium. Now the question is do you know how and where the coolant is getting out? Do you know for a fact that the pressure cap is lifting or are you assuming that is the case? Either way the cooling system pressure cannot be higher than 5 psig. So the question that logic says needs to be answered is where is the pressure escaping from? Maybe the expansion tank has a leak?
Once the system has heated up and has reached equilibrium the system pressure should not relax until the system has cooled down.
If you have not done so already you need to carry out a static pressure test at 15 psig and record the pressure versus time. If everything is working OK it should hold that pressure for a long time with a very slow rate of decay. Whether this test can replicate what happens when the motor is hot remains to be seen but it is about as close as one can get. If the system holds 15 psig then we need to scratch our heads a bit more.
As I can tell you are describing something similar to what happened previously. The information you have presented is not consistent with sound engineering logic. Either your temperature indication readings are wrong or you are not making pressure. Your cooling system cannot possibly boil up until the coolant temperature hits 250C if the system is holding pressure up to 15 psig- no need for debate on this.
Your description of events suggests to me that when your motor is hot it can only hold pressure up to about 5 psig as this is the equilibrium point corresponding to a water temperature of 220F. You stated that at this point the oil temperature soared- quite logical as the coolant has started boiling and thus the heat transfer coefficient has gone to rat sh*t , heat is staying in the motor so the oil temp goes up. However the indicated coolant temperature stays the same because it is now boiling. You slow down and reduce the heat load the system comes back to equilibrium. Now the question is do you know how and where the coolant is getting out? Do you know for a fact that the pressure cap is lifting or are you assuming that is the case? Either way the cooling system pressure cannot be higher than 5 psig. So the question that logic says needs to be answered is where is the pressure escaping from? Maybe the expansion tank has a leak?
Once the system has heated up and has reached equilibrium the system pressure should not relax until the system has cooled down.
If you have not done so already you need to carry out a static pressure test at 15 psig and record the pressure versus time. If everything is working OK it should hold that pressure for a long time with a very slow rate of decay. Whether this test can replicate what happens when the motor is hot remains to be seen but it is about as close as one can get. If the system holds 15 psig then we need to scratch our heads a bit more.
Last edited by mark kibort; 09-05-2017 at 06:47 PM.
09-05-2017, 07:11 PM
#29
Rennlist Member
Mark,
In post 24 you said that the water temps were 220F- that being the case the pressure would be limited to 5 psig. If your water temps did hit 250F then I would expect boiling to occur at the set pressure of the cap and that would be straight forward overheating causing coolant to puke out. The cap itself serves two functions- the primary one being to protect against over pressure and the secondary one is to act as a vacuum breaker so that when it cools off it sucks in air rather than collapsing the expansion tank due to vacuum.
Are you using a stock radiator? If you are and if you are using the in-tank coil as an oil cooler [as the earlier S4 models did] then it is not surprising that you are overheating at those ambient temperatures considering your power output. Indeed if that is your configuration it surprises me that you have got away with it for so long. Presumably you do not have the a/c condenser physically in the way? You certainly do not need the engine oil trying to re-heat the coolant.
In post 24 you said that the water temps were 220F- that being the case the pressure would be limited to 5 psig. If your water temps did hit 250F then I would expect boiling to occur at the set pressure of the cap and that would be straight forward overheating causing coolant to puke out. The cap itself serves two functions- the primary one being to protect against over pressure and the secondary one is to act as a vacuum breaker so that when it cools off it sucks in air rather than collapsing the expansion tank due to vacuum.
Are you using a stock radiator? If you are and if you are using the in-tank coil as an oil cooler [as the earlier S4 models did] then it is not surprising that you are overheating at those ambient temperatures considering your power output. Indeed if that is your configuration it surprises me that you have got away with it for so long. Presumably you do not have the a/c condenser physically in the way? You certainly do not need the engine oil trying to re-heat the coolant.
09-05-2017, 07:22 PM
#30
Rennlist Member
Thread Starter
Oh, that was a ball park guess.
yes, it was hot.. very hot. i dont know the exact temp, but it was boiling, as the fluild escaped the reservior. so, based on pressure of 15psi, yes, 250F would be the temp.
and yes, you are right, there is no chance of vacuum as we tested that cap last time, so that we know that function works
it cooled to a point where there was no boiling. mid scale i imagine. fans turning on, but no pressure in the lines. i was expecting vacuum when i opened it up, but there was nothing.. no pressure or sound when the cap was removed with lines soft and radiator hot enough to trigger fans activation. (standard 84 radiator sensor)
yes, stock radiator, nothing in the way... no condenser of course
works find if you have air flow... one time at thunderhill it started to over heat (top white line) so i cut a large hole in the front bumper. that solved it for the race , also a 100 degree day back in 2008. due to more power of the engine vs the stock motor.
obviously at the edge and yes, once the radiator starts to boil, that 260F oil doesnt help anything.. just goes thermal run away at that point.
so now you believe me that the engine can boil, condense and have no pressure in the lines after it cools on cool down lap? i should have let it run and build in the paddock to test the theory further.
yes, it was hot.. very hot. i dont know the exact temp, but it was boiling, as the fluild escaped the reservior. so, based on pressure of 15psi, yes, 250F would be the temp.
and yes, you are right, there is no chance of vacuum as we tested that cap last time, so that we know that function works
it cooled to a point where there was no boiling. mid scale i imagine. fans turning on, but no pressure in the lines. i was expecting vacuum when i opened it up, but there was nothing.. no pressure or sound when the cap was removed with lines soft and radiator hot enough to trigger fans activation. (standard 84 radiator sensor)
yes, stock radiator, nothing in the way... no condenser of course
works find if you have air flow... one time at thunderhill it started to over heat (top white line) so i cut a large hole in the front bumper. that solved it for the race , also a 100 degree day back in 2008. due to more power of the engine vs the stock motor.
obviously at the edge and yes, once the radiator starts to boil, that 260F oil doesnt help anything.. just goes thermal run away at that point.
so now you believe me that the engine can boil, condense and have no pressure in the lines after it cools on cool down lap? i should have let it run and build in the paddock to test the theory further.
Mark,
In post 24 you said that the water temps were 220F- that being the case the pressure would be limited to 5 psig. If your water temps did hit 250F then I would expect boiling to occur at the set pressure of the cap and that would be straight forward overheating causing coolant to puke out. The cap itself serves two functions- the primary one being to protect against over pressure and the secondary one is to act as a vacuum breaker so that when it cools off it sucks in air rather than collapsing the expansion tank due to vacuum.
Are you using a stock radiator? If you are and if you are using the in-tank coil as an oil cooler [as the earlier S4 models did] then it is not surprising that you are overheating at those ambient temperatures considering your power output. Indeed if that is your configuration it surprises me that you have got away with it for so long. Presumably you do not have the a/c condenser physically in the way? You certainly do not need the engine oil trying to re-heat the coolant.
In post 24 you said that the water temps were 220F- that being the case the pressure would be limited to 5 psig. If your water temps did hit 250F then I would expect boiling to occur at the set pressure of the cap and that would be straight forward overheating causing coolant to puke out. The cap itself serves two functions- the primary one being to protect against over pressure and the secondary one is to act as a vacuum breaker so that when it cools off it sucks in air rather than collapsing the expansion tank due to vacuum.
Are you using a stock radiator? If you are and if you are using the in-tank coil as an oil cooler [as the earlier S4 models did] then it is not surprising that you are overheating at those ambient temperatures considering your power output. Indeed if that is your configuration it surprises me that you have got away with it for so long. Presumably you do not have the a/c condenser physically in the way? You certainly do not need the engine oil trying to re-heat the coolant.