Hi, I just bought a 2000 f150 4.6, I've noticed that after I chut off the ignition theres a noise that sounds like a fan running but I don't think it's that radiator, is there something else that could be making this sound, it sounds more like moving air than a fan noise I think.

 

EGR or PCV valve will vent off any pressure still in the system when engine is shut off... kinda hard to describe the noise it makes...

 

yeah, that would make sense, I know a noise isn't much to go on.

 

does it go away after a few seconds ?? its kinda like a humming sound u can pop the hood and tap on the vacume solenoid if that is whats making the noise then its perfectly normal.

 

its the a.c. at least in my truck it is. try this. turn on the truck, and turn on the ac, leave it on for a while, then turn off the truck, and then turn off the ac, youll hear the pressure hissing away, and you wont get the hissing sound anymore. Besides, ac mechanics recommend to turn you ac off BEFORE turning the car off.

 

yup much better for the compressor

 

well the noise disappears when I turn off the lights, and comes back on with them , and no I'm not crazy , but I've only had the truck for a week and I still don't know what it is.

 

could be the alternator. but if u dont have any other problems other then a noise i wouldn worry about it. will only cost u major bucks to find the problem and fix it all for a noise that isnt hurting nothing

 

I have a 97 4.2L with a noise around the fuse block on the firewall on the passenger side. Can't figure if it is AC pressure or sounds kind of like electrical arching. Don't see or smell smoke so I'm guessing AC pressure.
Did not know about turning off AC before you shut off the truck. I'll start doing that. Thanks for the advice.