xCCTer

Can anyone tell me when the (B4P) boost fan in front of the radiator is supposed to come on? The main fan comes on at 228 and goes off about 213, but the boost fan never comes on. No overheating problem, but if it's on there I want it to work. Does the temperature sender on the left side of the block control the operation of the boost fan? Does it come on just when the a/c is turned on? Help if you can. Thanks!

tequilaboy

It needs to be pretty hot for the boost fan to come on something like 235-240 F.

It is triggered by the coolant temp switch on the drivers side head. You can get a lower temp switch that will turn the boost fan on at 200 and off at 180.

I used to have both my fans controlled by the 200 on/180 off switch. This works well with a lower temp thermostat, too.

Now I have both fans wired in parallel for common control by the ecm. I just unplugged the switch once I got into ecm tuning, since I had already wired them in parallel.

Steel Breeze

What tequilaboy said is accurate. I do know that the front pusher fan turns on like 5 degrees hotter, and off about 5 or so degrees hotter than the main fan. What I can't figure out, is why they didn't just hook them together. So they both just come on as stated above. My guess is to save on your alternator. However if both fans were on at the same time, they wouldn't be on as long as just the main fan. Love to be able to talk to the engineer/s that designed that. I would like to here there logic. They usually don't do these thing, unless there is a good reason. Thanks...

xCCTer

Thanks. I just want to make sure it works since it's on there. Relay is fine, switch is next.

xCCTer

Thanks for letting me pick your brain.