| I've been concerned with potential overheating issues as a result of the electric water pump mod failing. Not that I expect it to, but on that same token I wanted to implement some form of warning to indicate to me if something wasn't right. Something that came to mind was quite simple and could easily be implemented by anyone. HEre's the idea: The auxiliary fan is controlled by the ECU. It will turn the AUX fan on dependent on coolant temperature and vehicle speed. The basic breakdown is different between the NA and TT models since the TT has a two speed aux fan and the NA is only a single speed, but here it is, summed up for purposes of a temperature warning lamp. These modes are ONLY the case when the AC is "OFF". NA AND TT: At ANY speed, if the coolant temperature is over 221F, it will turn the AUX fan on. 221F is the highest you ever want to see your coolant temperature getting up to. Going much higher (you have about 20F headroom from here) will risk warping the heads and breaching the head gasket. So here's the idea: Wire up a RED LED to the auxiliary fan and mount the lamp somewhere in clear view of the driver so that if it turns on, it will not be overlooked. Unfortunately, the temperature gauge sometimes does not get enough attention, and sometimes it is after "too late" and you already have a damaged engine. This mod would cost $0.99 for a 12V LED and a minimal amount of wire routing down to the ECU itself. The output wire on the ECU is pin #19; almost dead-center on the connector; blue wire, 2nd position from center. It is the only blue wire in the 2nd position from center. Refer to a FSM for the actual wire to see its location. This wire goes +12V to turn the AUX fan relay on, which supplies power to the fan itself. Ground the (-) terminal of the LED and run a single wire from the LED's (+) terminal and splice into this output line on the ECU. Keep in mind, the indicator will tell you if you are over 221F ONLY when the AC is turned off. If the AC is on, the light will illuminate at a slightly lower temperature dependent on speed, however, the temperatures it will turn on at with the AC "ON", are still higher than what you would want the engine running at. On the NA, the lamp will turn on at 203F with the AC on and the TT, it will turn on at 212F. Refer to the FSM for a further breakdown of this dependent on speed. FWIW, the factory temperature gauge will not move between 180F and 220F, and then it quickly spikes up from there. I suppose Nissan did this because they dont want a bunch of people saying that "sometimes my car runs hot and sometimes it doesnt" and bringing the vehicles in for inspection by a dealer/mechanic, etc. The only problem with this is that after you breach 220F, it QUICKLY rises and you would have no indication prior that the engine was alreaedy running a little on the warm side (be it due to environmental conditions, defective cooling system/fan, etc, or other causes). This way, you will have a bright RED led peering you in the eye to tell you that you are reaching a critical temperature. I know I've overlooked the temperature sensor before - countless occasions. How often do you look at yours? Remember, when the engien starts to overheat above 220F, the gauge will quickly rise. Cruising down the interstate at 70+MPH, "in the zone", you likely wont see the temp gauge rise until it is too late. :-/
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