Cooling a Supercharged S4
05-21-2015, 11:09 AM
#16
Three Wheelin'
I recall - correct me if I am wrong here please - that there is an oil cooler thermostat that has a large effect on cooling at high temperatures as it allows the max flow of oil through the oil cooler. This happens when the water (for lack of a better word) cooling system max's out.
When I did the supercharger on my '91 GT, I recall that we put in a new oil cooler thermostat to ensure that the oil cooling system would be operating effectively.
When I did the supercharger on my '91 GT, I recall that we put in a new oil cooler thermostat to ensure that the oil cooling system would be operating effectively.
05-21-2015, 06:20 PM
#17
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Too bad the prior owner screwed up what used to be a pretty nice 14 sec 1/4 mile 170 MPH car that could drive anywhere with A/C..... sounds like he too drank the Kool-Aid.
Using a lower temp thermostat might give you a few more minutes before melt down but is really not a fix.
Using a lower temp thermostat might give you a few more minutes before melt down but is really not a fix.
05-21-2015, 09:02 PM
#19
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I agree with much of what has been said. I have a 16V 928 Motorsports stage II kit. The IC radiator is in front of the driver's side wheel. Frankly I rarely use it. I have removed the fuse for the fan in normal use. I use the IC itelf as a heat sink intercooler which works great for intermittant surges of power. Between power surges, the IC is cooled off by air being sucked through it, then when on boost, the IC cools that air too. Obviously this would not work on a constant level, but it works fine for me.
I also agree that you should remove the ICR and put a 16" fan. I use FF Dynamics, and they make a great fan. The ICR is acting as a major obstruction. I use 4 8" puller fans as well, also FF Dynamics.
Make sure your cooling system is completely burped and not leaking. Check the radiator cap. Check your AFR. Lean conditions can cause heat. If you live in a frost free area, look into what the best coolant mix would be.
Just some ideas.
Good luck,
Dave
I also agree that you should remove the ICR and put a 16" fan. I use FF Dynamics, and they make a great fan. The ICR is acting as a major obstruction. I use 4 8" puller fans as well, also FF Dynamics.
Make sure your cooling system is completely burped and not leaking. Check the radiator cap. Check your AFR. Lean conditions can cause heat. If you live in a frost free area, look into what the best coolant mix would be.
Just some ideas.
Good luck,
Dave
05-21-2015, 10:36 PM
#20
Track Day
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Thanks Dave. I wondered how on earth this car could be adequately cooled with 3 stacked radiators & only one small pusher fan mounted on the front of the I/C radiator. I doubt whether much (if any) cool air is making it's way to the engine radiator. Summer in Western Australia is pretty brutal: this cooling system will need to be well-sorted.
What is involved in relocating the I/C radiator + fan? I have a Euro (RHD) spec - which side would the I/C radiator fit in?
What is involved in relocating the I/C radiator + fan? I have a Euro (RHD) spec - which side would the I/C radiator fit in?
I agree with much of what has been said. I have a 16V 928 Motorsports stage II kit. The IC radiator is in front of the driver's side wheel. Frankly I rarely use it. I have removed the fuse for the fan in normal use. I use the IC itelf as a heat sink intercooler which works great for intermittant surges of power. Between power surges, the IC is cooled off by air being sucked through it, then when on boost, the IC cools that air too. Obviously this would not work on a constant level, but it works fine for me.
I also agree that you should remove the ICR and put a 16" fan. I use FF Dynamics, and they make a great fan. The ICR is acting as a major obstruction. I use 4 8" puller fans as well, also FF Dynamics.
Make sure your cooling system is completely burped and not leaking. Check the radiator cap. Check your AFR. Lean conditions can cause heat. If you live in a frost free area, look into what the best coolant mix would be.
Just some ideas.
Good luck,
Dave
I also agree that you should remove the ICR and put a 16" fan. I use FF Dynamics, and they make a great fan. The ICR is acting as a major obstruction. I use 4 8" puller fans as well, also FF Dynamics.
Make sure your cooling system is completely burped and not leaking. Check the radiator cap. Check your AFR. Lean conditions can cause heat. If you live in a frost free area, look into what the best coolant mix would be.
Just some ideas.
Good luck,
Dave
05-21-2015, 10:36 PM
#21
Track Day
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Thanks Cameron, I will investigate this option 
I recall - correct me if I am wrong here please - that there is an oil cooler thermostat that has a large effect on cooling at high temperatures as it allows the max flow of oil through the oil cooler. This happens when the water (for lack of a better word) cooling system max's out.
When I did the supercharger on my '91 GT, I recall that we put in a new oil cooler thermostat to ensure that the oil cooling system would be operating effectively.
When I did the supercharger on my '91 GT, I recall that we put in a new oil cooler thermostat to ensure that the oil cooling system would be operating effectively.
05-21-2015, 10:43 PM
#22
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Thank you Carl. The radiator is well sealed at the top and sides however it's possible the belly pan is missing (there is no cover underneath the front of the car - not sure if this is normal). I should check to make sure the 3 small fans on the rear of the engine radiator are "pulling". The 2 fans on the right side (facing the front of the car) don't have a full shroud over them, they are just attached to the back of the radiator. Perhaps fitting a shroud over both of them and that section of the radiator might help them to work more efficiently.
You could move the heat exchanger into the fender well - thats where we put it on the 16v cars. I saw a picture above that looked right. That would help.
Other ideas:
Use a Water Wetter or similar to bring the temps down, a lower thermostat that opens sooner, remove the temp switch from the fans and wire the fans so they are just ON when the key is on, make damn sure the radiator is sealed top, bottom, and sides so that air cannot go around it (common mistake), and check your coolant level and do not run a lower freezing point than you need to. Less anti-freeze and more water will lower your temps.
Other ideas:
Use a Water Wetter or similar to bring the temps down, a lower thermostat that opens sooner, remove the temp switch from the fans and wire the fans so they are just ON when the key is on, make damn sure the radiator is sealed top, bottom, and sides so that air cannot go around it (common mistake), and check your coolant level and do not run a lower freezing point than you need to. Less anti-freeze and more water will lower your temps.
05-21-2015, 10:47 PM
#23
Rennlist Member
Thanks Dave. I wondered how on earth this car could be adequately cooled with 3 stacked radiators & only one small pusher fan mounted on the front of the I/C radiator. I doubt whether much (if any) cool air is making it's way to the engine radiator. Summer in Western Australia is pretty brutal: this cooling system will need to be well-sorted.
What is involved in relocating the I/C radiator + fan? I have a Euro (RHD) spec - which side would the I/C radiator fit in?[/QUOTE]
I would pull the wheelwell liner from both front wheels and look and see what kind of room you have. There are also slightly smaller coolers with 8" fan that will serve the function. The rest is just wiring and rubber hose work. You will possibly lose part of the liner on one side. Here's mine in front of left side wheel.
[QUOTE=juju;12300731]
Dave
What is involved in relocating the I/C radiator + fan? I have a Euro (RHD) spec - which side would the I/C radiator fit in?[/QUOTE]
I would pull the wheelwell liner from both front wheels and look and see what kind of room you have. There are also slightly smaller coolers with 8" fan that will serve the function. The rest is just wiring and rubber hose work. You will possibly lose part of the liner on one side. Here's mine in front of left side wheel.
[QUOTE=juju;12300731]Dave
05-21-2015, 10:49 PM
#24
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Cheers Alan, this is what I'm thinking too. The 3 fans installed at the rear of the radiator, I think, came with the 928 Motorsports Stage 2 kit. I'm not sure of their specs. There is definitely no room at the back of the radiator to fit a large puller fan because the supercharger is in the way. I'm wondering whether fitting a shroud over the 2 fans mounted on the passenger side of the rear of the radiator might improve their efficiency.
As for the oil cooler suggestion: is there any type you recommend? Where would you locate an oil cooler?
As for the oil cooler suggestion: is there any type you recommend? Where would you locate an oil cooler?
This is what I am thinking too. That IC rad looks silly there, impedes airflow and heats up what it doesn't impede - but mainly it stops you putting a big pusher fan on the front - which I think you should consider also... take it in steps...
1) Measure accurately
2) Test functionally
3) Improve heat exchanges
- water wetter
- remove airflow restrictions
- ensure good flow through shrouding for the pullers
4) Remove additional heat loads
- intercooler rad
- add late model air/oil cooler before rad side tank to reduce oil thermal load
5) Better fans
The thermostat temp makes little difference - you either have enough cooling capacity or not - and if you don't: starting lower hardly has any effect - it has exactly no effect on the worst case conditions => always a waste of time.
Set the thermostat for the temp you want to run at for best results - and that isn't cold.
Alan
1) Measure accurately
2) Test functionally
3) Improve heat exchanges
- water wetter
- remove airflow restrictions
- ensure good flow through shrouding for the pullers
4) Remove additional heat loads
- intercooler rad
- add late model air/oil cooler before rad side tank to reduce oil thermal load
5) Better fans
The thermostat temp makes little difference - you either have enough cooling capacity or not - and if you don't: starting lower hardly has any effect - it has exactly no effect on the worst case conditions => always a waste of time.
Set the thermostat for the temp you want to run at for best results - and that isn't cold.
Alan
05-21-2015, 10:58 PM
#25
Rennlist Member
Hi Juju,
Here's a thread I ran about adding to the cooling capacity of my 16V SC.
https://rennlist.com/forums/928-foru...or-16v-sc.html
Dave
Here's a thread I ran about adding to the cooling capacity of my 16V SC.
https://rennlist.com/forums/928-foru...or-16v-sc.html
Dave
05-22-2015, 02:14 AM
#26
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there comes a time in the year here in Vegas where my car will always run hot. The cooling system is basically maxed out in a NA car at the temps we see out here in the summer. If i put any long stretches of boost in it during stop and go traffic it will get hot. Many times it will never fully cool down on the freeway either with more than adequate airflow..
Im thinking about adding more radiator capacity some how.
Im thinking about adding more radiator capacity some how.
05-22-2015, 06:54 AM
#27
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As you can see from the various inputs the 928 cooling system is just about adequate in a hot climate if everything is working as designed. When a power booster is added the demand on the cooling system increases although by exactly how much I do not know.
On your [89] model I have a feeling the engine oil cooler is still in the end tank [hot side] of the radiator. For sure 90 onwards have the oil cooler under the radiator and that has been challenged with some re-introducing the radiator into the oil cooling circuit for additional oil cooling effect. Unfortunately the stock system does not monitor oil temperature but it is a fair bet that if the cooling system temperature is too high so will the oil temperature.
Given your current [lower] ambient temperatures I remain suspicious of the numbers you reported- they may be false or something could indeed be working incorrectly but I am far from convinced that it is the s/c kit that is solely responsible for what you are seeing based on what you have reported but as Tony indicates on his T/S setup it will be limiting in summer time.
As someone with 16 years of 928 ownership experience in one of the hottest climates in the world you can consider the following to enhance:
1. Coolant composition- pure water is facilitates heat transfer significantly better than a 50/50 glycol mix. Do you ever see frost in Perth? You can run with a 75/25 mix providing you ensure you have adequate anti corrosion chemicals in the mix [glycol lasts forever- the chemical package about 2 years- modern super-coolants excluded].
2. Redline water wettter should be mandatory for your 928. I use a 70/30 mix with a bottle of this stuff and stick another bottle in after two years- after 4 years I change the job lot.
3. Fans help the car at idle and low speeds- personally I think they make little to no difference when cruising/powering along.
4. I have serious doubts about the adequacy of the external oil cooler on my model but I feel it is better than placing additional load on the radiator.
5. The earlier 32V manual transmission models have no transmission oil cooler and their a/c condenser fills the gap taken by transmission coolers- their a/c systems work better in hot climates. I am not sure of the air temperature leaving the condenser [or the transmission cooler] but I suspect it will add in the region of 20 degrees C to the air temperature hitting the radiator. Get rid of these obstacles and the radiator will perform better. I have not done this but it is on my project radar. A French chap over here modified his 928 to place the a/c condenser at the back of the car- I thought it would not work -in fact it worked very well- looked a bit crappy of course but not that bad to be fair.
6. Sticking an intercooler in front of this "already challenged lot" is just not too clever in a hot climate- I would say this has to be relocated no matter what your problems are caused by.
7. Air cannot flow through through blocked radiator matrices. Make sure you radiator is externally cleaned- you may be amazed at how much crap can accumulate between the a/c condenser and the radiator and end up trapped in the air fins . If you remove the fan shroud you can easily undo the top mounts and ease the radiator back a bit to see what it looks like in there. You can also back flush with a hose pipe to help wash any gunge out. I do not know whether the s/c location will let you do this though.
8. The radiator- the stock radiator is a pretty good piece of kit- it can be improved upon with a thicker matrix but the heat rejection rate at best will only improve by about 5% to 10%- still worth having if you have to replace the radiator.
9. I took the auto transmission cooler out of the radiator on my 928 and rely on the air cooler only. I mitigate this by changing the ATF more frequently. I would not be happy with this if I was producing a lot more power though.
So, if I was going to run with your setup in a hottish climate I would do all that I have done to date plus consider the following in order of priority:
1. relocate the intercooler
2. Take oil cooling out of the radiator and at the very least upgrade to the 90 oil cooler- preferably a better cooler with auxiliary fan.
3. Upgrade the transmission cooling
4. Move the a/c condenser to the rear of the car[ if the above prove to be inadequate].
The wheel wells offer two location spots-obviously space is the limiting factor.
The above reflects my experience running the 928 in a very hot climate.
Rgds
Fred
On your [89] model I have a feeling the engine oil cooler is still in the end tank [hot side] of the radiator. For sure 90 onwards have the oil cooler under the radiator and that has been challenged with some re-introducing the radiator into the oil cooling circuit for additional oil cooling effect. Unfortunately the stock system does not monitor oil temperature but it is a fair bet that if the cooling system temperature is too high so will the oil temperature.
Given your current [lower] ambient temperatures I remain suspicious of the numbers you reported- they may be false or something could indeed be working incorrectly but I am far from convinced that it is the s/c kit that is solely responsible for what you are seeing based on what you have reported but as Tony indicates on his T/S setup it will be limiting in summer time.
As someone with 16 years of 928 ownership experience in one of the hottest climates in the world you can consider the following to enhance:
1. Coolant composition- pure water is facilitates heat transfer significantly better than a 50/50 glycol mix. Do you ever see frost in Perth? You can run with a 75/25 mix providing you ensure you have adequate anti corrosion chemicals in the mix [glycol lasts forever- the chemical package about 2 years- modern super-coolants excluded].
2. Redline water wettter should be mandatory for your 928. I use a 70/30 mix with a bottle of this stuff and stick another bottle in after two years- after 4 years I change the job lot.
3. Fans help the car at idle and low speeds- personally I think they make little to no difference when cruising/powering along.
4. I have serious doubts about the adequacy of the external oil cooler on my model but I feel it is better than placing additional load on the radiator.
5. The earlier 32V manual transmission models have no transmission oil cooler and their a/c condenser fills the gap taken by transmission coolers- their a/c systems work better in hot climates. I am not sure of the air temperature leaving the condenser [or the transmission cooler] but I suspect it will add in the region of 20 degrees C to the air temperature hitting the radiator. Get rid of these obstacles and the radiator will perform better. I have not done this but it is on my project radar. A French chap over here modified his 928 to place the a/c condenser at the back of the car- I thought it would not work -in fact it worked very well- looked a bit crappy of course but not that bad to be fair.
6. Sticking an intercooler in front of this "already challenged lot" is just not too clever in a hot climate- I would say this has to be relocated no matter what your problems are caused by.
7. Air cannot flow through through blocked radiator matrices. Make sure you radiator is externally cleaned- you may be amazed at how much crap can accumulate between the a/c condenser and the radiator and end up trapped in the air fins . If you remove the fan shroud you can easily undo the top mounts and ease the radiator back a bit to see what it looks like in there. You can also back flush with a hose pipe to help wash any gunge out. I do not know whether the s/c location will let you do this though.
8. The radiator- the stock radiator is a pretty good piece of kit- it can be improved upon with a thicker matrix but the heat rejection rate at best will only improve by about 5% to 10%- still worth having if you have to replace the radiator.
9. I took the auto transmission cooler out of the radiator on my 928 and rely on the air cooler only. I mitigate this by changing the ATF more frequently. I would not be happy with this if I was producing a lot more power though.
So, if I was going to run with your setup in a hottish climate I would do all that I have done to date plus consider the following in order of priority:
1. relocate the intercooler
2. Take oil cooling out of the radiator and at the very least upgrade to the 90 oil cooler- preferably a better cooler with auxiliary fan.
3. Upgrade the transmission cooling
4. Move the a/c condenser to the rear of the car[ if the above prove to be inadequate].
The wheel wells offer two location spots-obviously space is the limiting factor.
The above reflects my experience running the 928 in a very hot climate.
Rgds
Fred
Last edited by FredR; 05-22-2015 at 09:23 AM.
05-22-2015, 08:54 AM
#28
Three Wheelin'
One last thought. On my '91 GT I found that the bottom part of the stock radiator had been pretty clogged up with debris - old leaves and stuff that over time had plugged up a good 10 or 15% of the radiator. This was all near the bottom more concentrated in the middle where stuff was being sucked up off the road over many years I guess. There was no airflow through that part of the rad.
If you haven't checked that, you might want to. Of course, this idea or the oil cooler and thermostat idea don't help if your issue of overheating is at idle or off idle. Only in motion.
If you haven't checked that, you might want to. Of course, this idea or the oil cooler and thermostat idea don't help if your issue of overheating is at idle or off idle. Only in motion.
05-22-2015, 08:58 AM
#29
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Too bad the prior owner screwed up what used to be a pretty nice 14 sec 1/4 mile 170 MPH car that could drive anywhere with A/C..... sounds like he too drank the Kool-Aid.
Using a lower temp thermostat might give you a few more minutes before melt down but is really not a fix.
Using a lower temp thermostat might give you a few more minutes before melt down but is really not a fix.
"My 928 runs hot" threads are probably only outnumbered by "what oil should I use" and "Does this watch go with stitching on the seats in my Porsche"...........well, that last one is mostly in the 997/991 forum.
05-22-2015, 10:01 AM
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Thank you very much Fred - and Alan, Dave, Erik, Cameron & everyone else - for taking the time to contribute your thoughts to this thread, I greatly appreciate it.
One thing I need to clarify: the stock radiator in my 928 has been removed - the previous owner replaced the stock radiator with a larger 928 Motorsports aluminium radiator when the s/c was fitted. My radiator has at least one end tank (it has oil lines running into it) on the passenger (LH) side. I haven't been able to get a good look at the driver (RH) side of the tank to see if it has an end tank. The surface area of the front of the radiator is about 85% - 90% covered by the A/C condenser so it's hard to see how clean / debris free it is but it looks pretty good. I will take a few photos tomorrow morning.
It is booked in for a service on 10 June however I think I will change the oil (just need to find where to buy Mann filters in Perth, or else something equivalent!) and flush the radiator ASAP (using a 25/75 coolant/water mix) and just ask the mechanic to perform some diagnostics on the cooling system and engine. The hoses all look good but I have no idea when the water pump, thermostat, seals etc were last checked/replaced.
I like the idea of the intercooler radiator wheel-well relocation as a nice little weekend DIY but I don't want to get ahead of my self or my limited skill set!
One thing I need to clarify: the stock radiator in my 928 has been removed - the previous owner replaced the stock radiator with a larger 928 Motorsports aluminium radiator when the s/c was fitted. My radiator has at least one end tank (it has oil lines running into it) on the passenger (LH) side. I haven't been able to get a good look at the driver (RH) side of the tank to see if it has an end tank. The surface area of the front of the radiator is about 85% - 90% covered by the A/C condenser so it's hard to see how clean / debris free it is but it looks pretty good. I will take a few photos tomorrow morning.
It is booked in for a service on 10 June however I think I will change the oil (just need to find where to buy Mann filters in Perth, or else something equivalent!) and flush the radiator ASAP (using a 25/75 coolant/water mix) and just ask the mechanic to perform some diagnostics on the cooling system and engine. The hoses all look good but I have no idea when the water pump, thermostat, seals etc were last checked/replaced.
I like the idea of the intercooler radiator wheel-well relocation as a nice little weekend DIY but I don't want to get ahead of my self or my limited skill set!
As you can see from the various inputs the 928 cooling system is just about adequate in a hot climate if everything is working as designed. When a power booster is added the demand on the cooling system increases although by exactly how much I do not know.
On your [89] model I have a feeling the engine oil cooler is still in the end tank [hot side] of the radiator. For sure 90 onwards have the oil cooler under the radiator and that has been challenged with some re-introducing the radiator into the oil cooling circuit for additional oil cooling effect. Unfortunately the stock system does not monitor oil temperature but it is a fair bet that if the cooling system temperature is too high so will the oil temperature.
Given your current [lower] ambient temperatures I remain suspicious of the numbers you reported- they may be false or something could indeed be working incorrectly but I am far from convinced that it is the s/c kit that is solely responsible for what you are seeing based on what you have reported but as Tony indicates on his T/S setup it will be limiting in summer time.
As someone with 16 years of 928 ownership experience in one of the hottest climates in the world you can consider the following to enhance:
1. Coolant composition- pure water is facilitates heat transfer significantly better than a 50/50 glycol mix. Do you ever see frost in Perth? You can run with a 75/25 mix providing you ensure you have adequate anti corrosion chemicals in the mix [glycol lasts forever- the chemical package about 2 years- modern super-coolants excluded].
2. Redline water wettter should be mandatory for your 928. I use a 70/30 mix with a bottle of this stuff and stick another bottle in after two years- after 4 years I change the job lot.
3. Fans help the car at idle and low speeds- personally I think they make little to no difference when cruising/powering along.
4. I have serious doubts about the adequacy of the external oil cooler on my model but I feel it is better than placing additional load on the radiator.
5. The earlier 32V manual transmission models have no transmission oil cooler and their a/c condenser fills the gap taken by transmission coolers- their a/c systems work better in hot climates. I am not sure of the air temperature leaving the condenser [or the transmission cooler] but I suspect it will add in the region of 20 degrees C to the air temperature hitting the radiator. Get rid of these obstacles and the radiator will perform better. I have not done this but it is on my project radar. A French chap over here modified his 928 to place the a/c condenser at the back of the car- I thought it would not work -in fact it worked very well- looked a bit crappy of course but not that bad to be fair.
6. Sticking an intercooler in front of this "already challenged lot" is just not too clever in a hot climate- I would say this has to be relocated no matter what your problems are caused by.
7. Air cannot flow through through blocked radiator matrices. Make sure you radiator is externally cleaned- you may be amazed at how much crap can accumulate between the a/c condenser and the radiator and end up trapped in the air fins . If you remove the fan shroud you can easily undo the top mounts and ease the radiator back a bit to see what it looks like in there. You can also back flush with a hose pipe to help wash any gunge out. I do not know whether the s/c location will let you do this though.
8. The radiator- the stock radiator is a pretty good piece of kit- it can be improved upon with a thicker matrix but the heat rejection rate at best will only improve by about 5% to 10%- still worth having if you have to replace the radiator.
9. I took the auto transmission cooler out of the radiator on my 928 and rely on the air cooler only. I mitigate this by changing the ATF more frequently. I would not be happy with this if I was producing a lot more power though.
So, if I was going to run with your setup in a hottish climate I would do all that I have done to date plus consider the following in order of priority:
1. relocate the intercooler
2. Take oil cooling out of the radiator and at the very least upgrade to the 90 oil cooler- preferably a better cooler with auxiliary fan.
3. Upgrade the transmission cooling
4. Move the a/c condenser to the rear of the car[ if the above prove to be inadequate].
The wheel wells offer two location spots-obviously space is the limiting factor.
The above reflects my experience running the 928 in a very hot climate.
Rgds
Fred
On your [89] model I have a feeling the engine oil cooler is still in the end tank [hot side] of the radiator. For sure 90 onwards have the oil cooler under the radiator and that has been challenged with some re-introducing the radiator into the oil cooling circuit for additional oil cooling effect. Unfortunately the stock system does not monitor oil temperature but it is a fair bet that if the cooling system temperature is too high so will the oil temperature.
Given your current [lower] ambient temperatures I remain suspicious of the numbers you reported- they may be false or something could indeed be working incorrectly but I am far from convinced that it is the s/c kit that is solely responsible for what you are seeing based on what you have reported but as Tony indicates on his T/S setup it will be limiting in summer time.
As someone with 16 years of 928 ownership experience in one of the hottest climates in the world you can consider the following to enhance:
1. Coolant composition- pure water is facilitates heat transfer significantly better than a 50/50 glycol mix. Do you ever see frost in Perth? You can run with a 75/25 mix providing you ensure you have adequate anti corrosion chemicals in the mix [glycol lasts forever- the chemical package about 2 years- modern super-coolants excluded].
2. Redline water wettter should be mandatory for your 928. I use a 70/30 mix with a bottle of this stuff and stick another bottle in after two years- after 4 years I change the job lot.
3. Fans help the car at idle and low speeds- personally I think they make little to no difference when cruising/powering along.
4. I have serious doubts about the adequacy of the external oil cooler on my model but I feel it is better than placing additional load on the radiator.
5. The earlier 32V manual transmission models have no transmission oil cooler and their a/c condenser fills the gap taken by transmission coolers- their a/c systems work better in hot climates. I am not sure of the air temperature leaving the condenser [or the transmission cooler] but I suspect it will add in the region of 20 degrees C to the air temperature hitting the radiator. Get rid of these obstacles and the radiator will perform better. I have not done this but it is on my project radar. A French chap over here modified his 928 to place the a/c condenser at the back of the car- I thought it would not work -in fact it worked very well- looked a bit crappy of course but not that bad to be fair.
6. Sticking an intercooler in front of this "already challenged lot" is just not too clever in a hot climate- I would say this has to be relocated no matter what your problems are caused by.
7. Air cannot flow through through blocked radiator matrices. Make sure you radiator is externally cleaned- you may be amazed at how much crap can accumulate between the a/c condenser and the radiator and end up trapped in the air fins . If you remove the fan shroud you can easily undo the top mounts and ease the radiator back a bit to see what it looks like in there. You can also back flush with a hose pipe to help wash any gunge out. I do not know whether the s/c location will let you do this though.
8. The radiator- the stock radiator is a pretty good piece of kit- it can be improved upon with a thicker matrix but the heat rejection rate at best will only improve by about 5% to 10%- still worth having if you have to replace the radiator.
9. I took the auto transmission cooler out of the radiator on my 928 and rely on the air cooler only. I mitigate this by changing the ATF more frequently. I would not be happy with this if I was producing a lot more power though.
So, if I was going to run with your setup in a hottish climate I would do all that I have done to date plus consider the following in order of priority:
1. relocate the intercooler
2. Take oil cooling out of the radiator and at the very least upgrade to the 90 oil cooler- preferably a better cooler with auxiliary fan.
3. Upgrade the transmission cooling
4. Move the a/c condenser to the rear of the car[ if the above prove to be inadequate].
The wheel wells offer two location spots-obviously space is the limiting factor.
The above reflects my experience running the 928 in a very hot climate.
Rgds
Fred