| The cooling system in the Z32 is quite robust even in stock form and it can dissipate an appreciable quantity of heat even in the most severe conditions, however, there are several facets to this system that must be in proper working order else it will quickly fail in adequacy. The components of the system are quite simple in and of themselves, mostly crude devices actually, but they all work in tandem to form a somewhat complex system. Even when all of the components of the system are working properly, not always will you have adequate cooling capacity. I wanted to share some of my expertise here mostly for the fact that if you overheat the engine, it can cause a number of catastrophic failures to occur, and no one wants to see that happen. The system layout:
 AIRFLOW There are two forces at work here and a third additional "switched" source. 1) Primary Radiator Fan: mechanical or electric
2) Ram-Air force: when vehicle is in forward motion
3) Auxiliary Fan: Switched based on temp, AC, and speed condition Airflow is critical to the operation of the cooling system. Without proper airflow, the radiator will not be able to dissipate the heat into the air and the system will overheat as soon as your heat input exceeds your heat output. The order in which these elements are given is arbitrary as the actual path of airflow is a bit different as seen in the diagram. The airflow route is always the same: In through the fascia's opening, through the auxiliary fan, through the AC Condenser, into the radiator, and finally out through the mechanical/electric fan. There are a couple of different components that the air must move through before it finally moves through the radiator core and works its magic. The fascia inlet duct is of some importance - you obviously dont want to have this blocked off but that probably goes without mention. However, what apparently seems to elude most people is not the next item either (Aux Fan), but rather, the AC Condenser. I can't count the number of Z32s that have aftermarket radiators in them - I've seen more than I can count, but, I'd be willing to bet that out of the people reading this post, I can count the number of them on both hands that, prior to installation of their aftermarket radiator, they flushed out the AC condenser. Most people will pull out their old radiator and say, "Wow, look at all the crud in the face of this thing!" and never consider that what you see is the aftermath of what the AC condenser has already filtered out. BACKWASH YOUR AC CONDENSER. This is quite easily done and will only take about an hour to an hour.5. The process is simple: Remove radiator, unbolt oil cooler (leave lines connected), remove auxiliary fan, remove fascia underpanel (the wide black plastic underskirt). Obtain a spray bottle of Purple Power (most automotive stores carry this) and liberally spray down the back and front of the AC condenser. Let it sit for 20 minutes while you connect your garden hose to your hot-water heater and attach a suitable spray nozzle. BACKFLUSH the AC condenser: this means spraying the water jet into the backside of the AC condenser; the side closest to the engine. You will be AMAZED at how much sand and debris comes out of it. Repeat process two more times as one round definately will not remove 10+ years of collected road grime. You can spray out the water with a compressed air tip if you have one, but not a necessary procedure. Just doing this one simple procedure will undoubtedly lower your operating temperatures. In the summer heat, the system will not be able to maintain a 170-180F temperature while just cruising, which tells you that the system is already operating at full duty: as you lay more and more into the long pedal on the right, you are only going to see an increase in coolant temperature from there. However, the efficiency of the system is profoundly improved as airflow through the radiator is increased. A clean AC condenser will suprise you with how much cooler the system will operate: not just engine temperature, but also your AC system will work more efficiently and provide better cabin cooling, so, take a little time to do yourself a favor. :) Primary Radiator Fan (mechanical or electric):
The mechanical fan is driven by the same belt that drives the water pump and the alternator, however, the mechanical fan incorporates a thermostatic clutch mechanism that varies the amount of torque transferred into driving the fan. The clutch is a passive mechanical device that manipulates the torque transfer quantity based on temperature. At the front of the fan clutch assembly is a bi-metallic coil ([ http://en.wikipedia.org/wiki/Bi-metal ]) that adjusts the amount of resistance the clutch offers: the more resistance, the faster it will drive the fan speed. The bi-metal coil and clutch assembly is designed to increase the torque transfer as the temperature increases. Since the thermostatic clutch is positioned directly behind the radiator and the radiator is dissipating heat into the air, it is in perfect position to control the fan speed. Over time and use, the clutch mechanism will begin to slip and not offer as much driving force for the fan. The internal mechanism of the fan clutch is similar to that of a viscous slip differential and it contains a fluid. The thermatic control mechanism has a control input shaft which also has a seal - over time, this seal will begin to leak and the fluid will be spun out of the clutch. Eventually this will reach a breaking point where you cannot move enough air through the radiator to keep the engine within normal operating temperatures. But, just because you dont see traces of fluid leakage from the input control shaft does not mean your clutch isn't defective. There are other items within the device that can cause it to function improperly. Given the expense of this part as compared to the rest, it is advised to go through all other checkpoints prior to replacing this. If you have an electric fan setup, you will avoid the pitfalls of a failing fan clutch, but an electric setup presents both its own benefits as well as potential pitfalls. Given the nature of electronic systems, eventually something will wear out: be it the electric motor or the fan control device (thermatic or simple relay). The best thing to rely on here is the temperature gauge, but even with an improperly installed setup or a clogged up AC condenser, this system will not work properly: it isn't magic.
Auxiliary Fan
The auxiliary fan's purpose is primarily to aid your AC system's operation. The aux fan is controlled via the ECU and is dependent on a few factors, namely temperature, but also dependent on whether the AC is on or not, and also based on vehicle speed. Refer to FSM EF&EC-31 for a detailed description of the operating parameters.
The other components within the system:
Water pump
Thermostat
Heater Core
Radiator Cap
Overflow Tank Water Pump:
This should be obvious what it does. I have not once seen a pump that has had defective impeller blades. I have seen otherwise in other severely neglected vehicles though: where the owner just kept putting straight water into the coolant system and without the ethylene glycol to act as a corrosion inhibitor and lubricant, it will quickly corrode the impeller blades into little pieces of rust, OR, trash the pump seal from lack of lubrication. If you are having overheating problems and your pump isn't leaking, so long as you haven't been just adding water to the system for months on end, your pump is not the culprit. Thermostat:
This device has a critical function in the system: it regulates the temperature of the water within the engine. Without this device, the cooling system will run constantly at 100% duty and the engine will take forever to warm up and not hold a consistent temperature. This unit works on the thermal expansion properties of materials. There is a control cylinder that is filled with wax and connected to the valve shaft portion of the thermostat. As the coolant increases in temperature, the wax will expand enough that it overcomes the resistance of the return spring and it will open. For kicks, I put an OEM thermostat in a pot of water and began heating the water up and monitoring the temperature of the water. The OEM thermostat is set to 76.5C (170F) and when the heated water achieved 170F, the valve in the thermostat just barely cracked open. So, the temperature stated on the thermostat is the cracking temperature, not the temperature at which it will maintain the engine at. When the engine duty increases, about 30% of the total energy of combustion is put directly into the cooling system. So, as engine duty increases, so will the cooling system's duty: this is facilitated by the thermostat. Its goal is to maintain the engine at a temperature slightly higher than the cracking temperature of the thermostat, but as I am sure most of you are aware, in summer temps and spirited driving, the cooling system will be working at full potential and engine temperatures will not maintain the same as on a cool day at idle. The most common failure mode of the thermostat is when the control cylinder's shaft seal fails. This will prohibit the thermostat from opening at all and it will quickly lead to an overheating condition. Given the amount of time required to replace this inexpensive part, it would be advised to eliminate other possibilities first such as backwashing the condenser and/or the radiator itself. Heater Core:
Although this is a component within the cooling system, it will never be a source of an overheating condition unless it is actually leaking coolant. Otherwise, this component can actually improve an overheating condition as I am sure most of you are aware of. Radiator Cap:
This is actually a critical component within the system - it isn't just a device used to cap off the radiator so that coolant doesn't splash out. The radiator cap's function is to control the cooling system's operating pressure as well as to handle the overflow/recovery system. The most widely known principle is that for every pound of pressure in a closed system the boiling point is increased three degrees. For example a 16-lbs. cap increases your boil-over point to 260 degrees (16x3=48). In most cases your motor will be junk after running above 230 for any length of time. But this pressure will suppress boiling while running and boil-over during heat swell that occurs when the engine is shut off. Getting back to the 230-degree mark, it is at this temperature that the incoming water is unable to control hot spots in the water jacket and steam pockets form. The water is diverted around these steam pockets and then all those really bad things happen; cracks, surface distortion and metal fatigue. The pressure produced by the water pump also controls these hot spots which occur around the combustion chambers and exhaust ports. The same boiling point law is in affect here. Overflow Tank:
Sometimes referred to as an expansion tank or air separator. Keeping the system full reduces aeration and allows it build pressure faster. As temperature increases the water expands and pressure builds. If the system is completely full the expansion pressure will exceed the cap pressure and over-flow into the recovery tank. Since our pressure cap is properly located at the highest point of the system, the air will be pushed out first. When the system cools and contracts a vacuum is created. Your radiator cap is equipped with a valve that opens under this negative pressure and will draw coolant back into the system through the tube that extends to the bottom of the recovery tank. If the recovery tank is kept half full (with the engine cold) every heat cycle will automatically purge more air out of the system. Potentially, the opposite is true without a recovery system. With every heat cycle water will be pushed out, leaving more air space this air space reduces the system pressure and boiling point. In closing: Recommended Operating Temperatures
There are a few different theories on coolant temperature and most have their place. Cold water (under 170F) and hot oil (230F) make power; this is a proven fact and the rule for drag racing. In most other forms of racing and street applications the engine is under power for minutes or hours rather than a few seconds. In this case higher temperatures in the range of 190 to 210F are necessary for engine components to normalize. Many inherent or design factors determine this temperature; block and head castings, metal properties, proper fuel combustion and machined clearances. Either inherently or by design the VG appears to prefer 180 to 195F for optimum power output but they appear to mechanically "sound" the best when they are running 200-210F as we tend to run larger piston-wall cleanrances for our boosted applications. Fuels react to temperatures related to engine temp and combustion pressure. Pumpfuel gasolines burn more completely at higher temperatures, so engines operating above 210F have reduced emissions and improved economy. Hopefully this will help some of you guys out even if you dont have a noted problem - given that we are likely going to see even higher temperatures this summer than the previous, it may even be a good idea to set aside some time to spend on inspecting and ensuring that your cooling system is operating the best it can. There's nothing worse than being stranded on the side of a hot summer road with a dead Z waiting for the flatbed to shovel you up..
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PSA: A good bit of something cool for the summer heat >>>> - 
15:53:26 06/07/06
