Hi-speed fan after shutoff


TRCM Author
May 25, 2001
I'm chasing an electrical gremlin. I have 2 Spal fans instead of the single stock one. I wired it so that the one fan comes on for low speed, and the other comes on for high speed.
If I drive the car around, it typically runs between 100 and 170, since that's what I programmed the chip for. If I turn on the A/C, it kicks on the other fan, but doesn't really cause the car to be any warmer, since it's around 50 degrees outside.
About 1 in 5 times, as I shut the car off, the hi fan will kick on and run for 10 minutes (and sometimes forever). If I unplug the fan timer relay connector, it of course stops. The timer relay is only about 4 years old (probably less than 10k miles on it). I did also recently replace the hi-speed relay near the timer relay, with no effect.
I can understand it getting stuck on, since maybe I'm trying to draw too many amps for the fans, but why would it come on in the first place? Bad temperature sensor in the intake?
What I understand is that if you shut your car off after the fan have been on high, they will continue to run for 10 minutes approx. If you shut your car off with the a/c on, the fans are supposed to run for 7 - 10 seconds afterwards...I do not know what logic the fan delay relay uses if you shut the car off with the a/c on and the temp above the high speed signal? I'd guess about 10 minutes and 10 seconds maybe, but not certain about this only. Every time we wash these cars we drowned the fan delay relay due to GM's inability to supply a shield like the p/s has. Perhaps your 'new' fan delay relay is hooped already?!