the two different speeds of the auxiliary fan. I have an electric fan in the car which is my primary cooling fan and still have the auxiliary fan in place.
I have changed the first turn-on temperature of the "low speed" circuit in the ECU to 170F. At 170F the ECU turns on the primary fan. Convenient too - once I start her up I'll let her idle until I hear the fan kick on.The second temperature parameter is set to 214F which pulls the "high speed" circuit to ground which is connected to a single-speed OEM auxiliary fan via a relay AND it pulls a ground on a small red led mounted into the lower bezel of the instrument cluster - can't miss it when it turns on but more than small enough that it goes unnoticed. Externally controlling these systems with a home-built temperature/speed pwm loop will work, but you are adding more complexity to the system than what the increase in failure probability is worth, not to mention the time and materials cost just to build a simple little controller. The ECU is already equipped with everything you need to achieve the same result with a lot less modification and using a lot more reliable circuitry. FWIW, if the OEM temp sensor fails (the one that the ECU uses, not the sensor for the gauge), the ECU will detect the fault and it treats the condition as if the engine is at -40C. This also forces the fans to run anytime the engine is running regardless of engine temperature and will indicate to you that the sensor has failed... not to mention the car wont run very well either since the enrichment value for the lowest temperature in the temp/enrichment table is some ridiculously high value that will make her run pig rich..... in short, the system will have fail safe, reliability, and can be done with virtually 99% of already existing control hardware that is already in the car. Additionally, concerning your desire to keep things quiet at idle/parking, the control loop for the aux fan also has parameters for vehicle speed that I believe can be tailored as well to meet your goal. Email me - I like this idea and I can help you out with the ECU side of this.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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