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My fans come on all the time, coming back from ATL last weekend, I stopped to get gas and the fans ran for about a minute after I turned off the car.
It was 82f outside, fans should not have come on in my opinion, is the temp range that low that the fans come on all the time after car is turned off or is my coolant that old, that it does not keep the car cool or worse, do I have a cooling issue?
I don't think it a problem. Note that they are activated whenever you turn on the AC. In addition they almost always come on for sometime after engine shutdown.
Heat soak is the phenomenon where the temp rises when you shut off the engine and the lack of coolant flow allows the temp in the radiator to increase which will kick on the fans even if they were not running while driving (with circulation and air flow).
Be sure you have the coolant topped up and that it is recent. If not flush and fill with proper coolant mixed with distilled water.
Before Christmas I had been stripping down my V8V to better understand some of the systems used and although the car has very few miles (7K) the components are a decade old and need inspection and possible replacement.
I'll note now that although I have not been overly impressed with the actual components used (this car is a Frankenstein of regular parts from other cars) the quality of workmanship in assembling the various components by AML employees is impressive. I.e. the use of thread lock and torque markings is better than I've seen in 3 decades of working on many Euro car makes.
I'll share a couple of discoveries - not sure if this is applicable to models after 2008 and this may already be well known but the fan setup in my V8V is derived from an older Ford design that is also used in Volvo, Mazda, Jaguar, BMW & a few others. I have found this to be a very efficient design and the only weakness I've witnessed comes from the terminal connections exposure to road salt (which is highly unlikely for most Aston Martins which are likely stored in winter months where road salt is used).
The situation of the fan assembly in the AM (behind the rad) is optimal and also serves to protect the fan module (which is also placed on the inward side and covered). Better yet, this method creates a "puller fan" effect which is more efficient for air movement through the rad fins.
How the system works:
The fans are activated via a PWM signal (pulse width modulation) from the PCM (Powertrain control module) The speed the each fan is commanded to spin is determined by various input factors, (Velocity, RPM, Engine coolant temperature, AC compressor request status, battery voltage etc) which PCM interprets and responds to by sending a variable PWM signal (fan speed) to the fan module (bolted on the fan shroud). AML refers to it as the Cooling fan motor control module. (CFMCM)
This fan module (CFMCM) takes the PWM signal and modifies the speed of fan motors using the DC 12V that is also supplied to the fan module (thick black & brown wires on a separate pigtail connector). The PWM signal wires are the thin green/yellow brown/yellow wires - on a separate connector pigtail.
The electric fans are activated by means of a fan module attached to the shroud. On the shroud the DC12v atthe pigtail are the thick Red(+) and Black(-) wires with the PWM signals carried through the thin white/green(+) & white/blue(+) wires. The motor control unit activates this power output stage by means of a square-wave signal with duty factors (variable pulse width) between 10 and 90 % thus controlling the various speeds of each electric fan. Pulse duty factors less than 5 % and greater than 95 % do not trigger activation but rather they are used for fault detection purposes.
It will be a while before I am able to analyse the full logic of Aston PCM but if it follows suit with this common Ford design then there are certain conditions that will be used to calculate the speed or activation of one or more fans.
1. Coolant temperature
2. Calculated catalyst temperature
3. Vehicle speed
4. Battery voltage
5. Air Conditioning pressure status
Other factors affecting Fan operation:
For the AC fan inputs the V8V uses a Trinary switch in the compressor discharge tube. This sends a signal to the PCM, to switch the
cooling fans to HIGH speed at 22 bar rising pressure and to LOW speed at 17,5 bar falling pressure. It also sends a hard-wired signal to the PCM, to switch the radiator cooling fans to LOW speed at 12 bar rising pressure and to switch the fans OFF at 8 bar falling pressure
After the engine is switched off, one or both fans may continue to operate at varying speeds (based on the PCM calculated catalyst and or ECT temperature). This will cool the radiator down from a heat surge.
As noted the fan speed is influenced by the engine coolant temperature and the pressure in the air conditioning system. The fan speed is also reduced as the vehicle speed increases. On other vehicles with similar systems (I.e. BMW M3) the same logic prevents fans from being turned on at speeds > 140 km/h as they are deemed unnecessary. I have not determined that speed for this setup however it is likely similar.
BTW - the fan in our V8V and DB9 is the same one used in the 97-02 Jaguar XK8. It is manufactured by the GATE division of Johnson Controls.
The Fan assembly (motors, shroud and control unit) is sold via a Jaguar part number: Part # MJB4270AB
The Fan shroud ONLY is part number: 824-0168
One last note - the radiator that the fan assembly in my V8V is connected to was also used in the Jaguar XK8 (Jaguar Part Number MJB4190AF) and is a very common part. The labels on both the rad and ac condenser from AML are from Visteon (a division of Ford - also acquired Johnson Controls - makers of the fan) Visteon UK plants were closed in 2010). Manufacturing was transferred to Mexico & USA. The same rad is made by Nissens and another version made by Spectra.
Last edited by BMW-North; Jan 14, 2017 at 05:46 PM.
