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I was reading in another thread that the 720S has two separate cooling systems with a common fill system and expansion tank. Evidently they have a high temp and low temp circuit with the engine and trans on the high temp circuit and the clutch and intercoolers on the low temp circuit.

Does anyone have any more info than this? Maybe a detailed explanation on how this setup works? Are there two temp sensors, one for the high temp and one for the low temp? It would be interesting to know the temp of the intercoolers versus the temp of the engine.
 

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i don't know for sure but since there is only 1 fill point and 1 expansion tank, my guess is that regular engine coolant gets routed to the low temp exchangers in front then coolant goes to intercoolers and returned to engine cooling system.
i've never heard of a second pump to circulate low temp fluid either,which would confirm my thought.
system works well but if it is setup as i've described,a separate system would be superior to control temps in intercoolers.
just my opinion! ymmv.
 

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All McLaren's have two circuits. The low temp as you said is for the chargecoolers. They are the small radiators up front, and purely are used to cool down the intake air temp through the chargecoolers (typically the term "intercooler" describes air-to-air cooling, and "chargecooler" describes a water-to-air system to cool the intake temps - though some people use them interchangeably).

The high temp circuit is the conventional radiators for the engine, and get their airflow from the side scoops.

Generally speaking, the temp of the low circuit is kinda irrelevant - what is relevant is the IAT (Intake Air Temp) which can be read via the OBD2 port. The temp of the high circuit of course is highly relevant, and thats your engine water temp gauge in the dash.

Thanks!

Z.
 

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Discussion Starter #4
Thanks for the responses guys.

Generally speaking, the temp of the low circuit is kinda irrelevant - what is relevant is the IAT (Intake Air Temp) which can be read via the OBD2 port. The temp of the high circuit of course is highly relevant, and thats your engine water temp gauge in the dash.
Wouldn't lowering the low circuit coolant temp lower the IAT's? I was hoping that there was some kind of temperature control of the low temp side but it doesn't look like there is.
 

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Thanks for the responses guys.


Wouldn't lowering the low circuit coolant temp lower the IAT's? I was hoping that there was some kind of temperature control of the low temp side but it doesn't look like there is.
Yes it will.
This applies to all cars that have air to water intercoolers. You isolate the low and high temp circuit. Add a larger reservoir tank with a pump to drive the fluid in the low temp circuit. This will increase fluid capacity which in turn will lower IATs and reduce heat soak.
 

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Thanks for the responses guys.


Wouldn't lowering the low circuit coolant temp lower the IAT's? I was hoping that there was some kind of temperature control of the low temp side but it doesn't look like there is.
There is no temp control - the system always runs at the highest efficiency that it can. In practice, the lower the IAT's the better under all circumstances (there's a possibility that you could go too cold, but it would be hypothetical as ambient temps are never low enough really to be an issue). Lowering the temp is just the easiest way for us to control air density - and the more dense, the more oxygen present, so we can put more fuel (to maintain the correct air to fuel ratio), and thus generate more power.

The low temp circuit therefore just tries to keep it as low as is practically possible by using a water jacket around an air chamber (chargecooler) to carry the heat away, cool it down via the front radiators, and back again - so there wouldn't be any kind of control on it.

Here are the main two ways you can bring the IAT's down further (for better power, or just to maintain power in hot weather):

1) Increase the capacity of the chargecooling circuit with larger radiators and larger volume of water. The larger radiators will help cool the water down faster while you're moving, and the larger volume will help the water absorb more heat and reduce heat soak (the increase in temps when you're sitting still). Road racing or spirited street driving doesn't experience much heat soak, whereas standing start racing (e.g. drag racing) does, and the power drop can be quite noticeable.

2) In practice, increasing the chargecooling capacity is not easy (as it requires physical space). Therefore, the easiest way is to use water injection after the intercooler/chargecooler. This injects highly atomized water directly in to the intake. As the water enters the cylinders, the water absorbs the heat, then evaporates, reducing the temperature of the air/fuel charge. This is highly effective in combating heat soak, and maintaining power levels. You can also mix in methanol (e.g. 50/50 mix of meth/water) to increase power (by increasing octane), but then you will need a tune to account for the extra fuel. Aquamist, Snow Performance and AEM are probably the most well known systems (in general stay away from on/off systems - a progressive system is much better).

Thanks!

Z.
 

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There is no temp control - the system always runs at the highest efficiency that it can. In practice, the lower the IAT's the better under all circumstances (there's a possibility that you could go too cold, but it would be hypothetical as ambient temps are never low enough really to be an issue). Lowering the temp is just the easiest way for us to control air density - and the more dense, the more oxygen present, so we can put more fuel (to maintain the correct air to fuel ratio), and thus generate more power.

The low temp circuit therefore just tries to keep it as low as is practically possible by using a water jacket around an air chamber (chargecooler) to carry the heat away, cool it down via the front radiators, and back again - so there wouldn't be any kind of control on it.

Here are the main two ways you can bring the IAT's down further (for better power, or just to maintain power in hot weather):

1) Increase the capacity of the chargecooling circuit with larger radiators and larger volume of water. The larger radiators will help cool the water down faster while you're moving, and the larger volume will help the water absorb more heat and reduce heat soak (the increase in temps when you're sitting still). Road racing or spirited street driving doesn't experience much heat soak, whereas standing start racing (e.g. drag racing) does, and the power drop can be quite noticeable.

2) In practice, increasing the chargecooling capacity is not easy (as it requires physical space). Therefore, the easiest way is to use water injection after the intercooler/chargecooler. This injects highly atomized water directly in to the intake. As the water enters the cylinders, the water absorbs the heat, then evaporates, reducing the temperature of the air/fuel charge. This is highly effective in combating heat soak, and maintaining power levels. You can also mix in methanol (e.g. 50/50 mix of meth/water) to increase power (by increasing octane), but then you will need a tune to account for the extra fuel. Aquamist, Snow Performance and AEM are probably the most well known systems (in general stay away from on/off systems - a progressive system is much better).

Thanks!

Z.
Well put, and might I add impressive :)
 

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Discussion Starter #8
Thanks Z! I really appreciate your explanation.

It would be interesting to find out the actual temperature of the low temp circuit. I would assume the high temp circuit's actual temperature is what is displayed on the dash.

I have a DynoJet 248 at my home that I am using to make a lot of dyno runs with my 720S. I am using a HP Tuners MPVI2 to log the data that is available. I plan on sharing my results after I get to a point where I have a better understanding of how this car operates.
 

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Im
Thanks Z! I really appreciate your explanation.

It would be interesting to find out the actual temperature of the low temp circuit. I would assume the high temp circuit's actual temperature is what is displayed on the dash.

I have a DynoJet 248 at my home that I am using to make a lot of dyno runs with my 720S. I am using a HP Tuners MPVI2 to log the data that is available. I plan on sharing my results after I get to a point where I have a better understanding of how this car operates.
I’m sure that the system is monitoring temps on the low circuit (at least for fan actuation and fault monitoring). I wouldn’t be surprised if there is a PID available on the OBD2 live data stream that displays it - I’ve just never looked for it 😜

Might also only be available on proprietary channels too (so only MDS or an MDS clone can read it).

I can check next time I’m in the technical manuals if there is an actual sensor. Might be able to just tap its signal - it’s probably going to either be a linear 0-5v or 0-12v (3-wire), or a basic thermistor (proportional resistance to temperature 2-wire) sensor. If the latter would just need to make sure whatever is rigged up to read it has a very high input impedance so as not to affect the actual signal to the control modules.

Thanks!

Z.
 

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There is no temp control - the system always runs at the highest efficiency that it can. In practice, the lower the IAT's the better under all circumstances (there's a possibility that you could go too cold, but it would be hypothetical as ambient temps are never low enough really to be an issue). Lowering the temp is just the easiest way for us to control air density - and the more dense, the more oxygen present, so we can put more fuel (to maintain the correct air to fuel ratio), and thus generate more power.

The low temp circuit therefore just tries to keep it as low as is practically possible by using a water jacket around an air chamber (chargecooler) to carry the heat away, cool it down via the front radiators, and back again - so there wouldn't be any kind of control on it.

Here are the main two ways you can bring the IAT's down further (for better power, or just to maintain power in hot weather):

1) Increase the capacity of the chargecooling circuit with larger radiators and larger volume of water. The larger radiators will help cool the water down faster while you're moving, and the larger volume will help the water absorb more heat and reduce heat soak (the increase in temps when you're sitting still). Road racing or spirited street driving doesn't experience much heat soak, whereas standing start racing (e.g. drag racing) does, and the power drop can be quite noticeable.

2) In practice, increasing the chargecooling capacity is not easy (as it requires physical space). Therefore, the easiest way is to use water injection after the intercooler/chargecooler. This injects highly atomized water directly in to the intake. As the water enters the cylinders, the water absorbs the heat, then evaporates, reducing the temperature of the air/fuel charge. This is highly effective in combating heat soak, and maintaining power levels. You can also mix in methanol (e.g. 50/50 mix of meth/water) to increase power (by increasing octane), but then you will need a tune to account for the extra fuel. Aquamist, Snow Performance and AEM are probably the most well known systems (in general stay away from on/off systems - a progressive system is much better).

Thanks!

Z.
I believe the 991 Porsche GT2 RS addresses the heat-soak issue causing high IAT by spraying water as you described in '2' above. A third method (or is this the GT2 RS method?) would be to spray the outside of the charge coolers with water since the ability for water to absorb heat is much greater than air.
 

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All Mclarens with stock cooling system suffer from heat soak.
Back to back runs on the dyno you will see the power curve drop.
Common trick in street racing when you are roll racing a Mclaren, do a few false starts to get the Mclaren heat soaked and then race them.
 

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Discussion Starter #12
All Mclarens with stock cooling system suffer from heat soak.
Back to back runs on the dyno you will see the power curve drop.
Common trick in street racing when you are roll racing a Mclaren, do a few false starts to get the Mclaren heat soaked and then race them.
I'm a little lost. You state that heat soak on the dyno will result in a power curve drop. However, when street racing getting the Mclaren heat soaked will increase the performance?
 

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heat soak applies to all vehicles. what makes the mclaren more prone? the turbos? the lack of low temp system cooling fans? the location of the h2o cooled intercoolers?
many non atmospherically charged vehicles have similar issues.

Also,there is only 1 cooling system unless someone can show me the existence of a second entirely separate system with it's own pump.
the way i understand it ,besides the physics and lexical semantics lessons given out here,the intercoolers (chargecoolers or whatever you opt to call them) are fed the exact same coolant the engine,clutch and tranny use.
the only difference is that this coolant is taken from the engine cooling system and bypassed into the intercooler system. All this means is that hot engine coolant (hopefully plucked coming out of the engine side mounted radiators and not going into them) is sent into the 2 front low temp radiators and then forwarded to the intercoolers after which it is returned to the engine cooling system.
If this is so,we are starting with an already fairly hot coolant and cooling it down as much as those 2 little radiators will allow.not an enviable system imo! And those low temp jobs do not have cooling fans,so there are no ptc,ntc,hall or molecular sensors that would attempt to regulate or control temperature. The only form of control is done via the intake air temp sensors which alter ecu info.
A real separate system would not intermingle high and low temp coolant,so NO,we do not have separate systems!
 
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