Originally Posted by
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just to follow up if anyone finds this looking to put the c7 fan on the c6 e38 ecm. the fan % doesn't work like you'd logically think.. it didn't hit me till I put 40% across the board in all the temp boxes and the fan % never moved. this ecm seems to use the same base logic of tuning on 2 fans using relays, and then uses a math filter to put a %DC for the fan module. so I found leaving the stock fan curve in there and just copy and paste it a box or 2 to the left, while making sure not to go over 40% in the first box, since that will make it run all the time. I went two to the left and with a 170deg stat(remember the ls stat is on the cold side input and always runs much higher than the stat temp, 187 stock stat runs 210-220) it seems to target and sit nicely around 196deg at 30% fan request, which is like 6amp load. very nice.
anyways, nice upgrade for 300$, moves a ton of air over stock and basically a direct hook up. you don't even need to tune the fan settings if you didn't change the stat.
oh and if you do it in a c6 I found running the power wire to the alternator lug, with an inline fuse, I used a jcase 60amp in 8ga wire, but c7 used a block style 80amp which would be nice to use. but if you go to the aux lug on the fuse box like I did at first, there's a good voltage drop by the time it gets there, the alt wire is pretty thick but it has a 14ga fusible link at the starter before running up to the fuse box. you're asking that 14ga wire to handle a good 80amps or more when the car has everything on max. they sell a wiring kit called the big 3 for the c6 which you could use for 120$, but eh, just moving the fan to the alt lug removes the fan load from the rest of the system, I measured 40amps with the fan commanded to 90% when running with my amp clamp. and only 34 when the car isn't running, so there's some limiting going on in the fan if the voltage isn't high enough. I feel like the alt lug is just a better spot for it and the test of the factory wiring.
lastly there's a fan setting that went the car is hot enough it. will run the fan for a few minutes at 60% with the car off to cool things down, I changed thst setting to 40% as that's about the same current draw as the stock fan at 60, and hopefully more airflow, but I can't measure airflow, so I went with amp load.