I have 94 f150 4x4 with a 5.8L engine that sounds different for no more than five minutes after start up and when the AC is going in stop and go traffic. After those five minutes after start up when it is all warmed up the truck sounds like a nice v8. The same thing goes after I start going down the road with the AC on. The engine sounds like the fan is moving faster than normal, but that is not the case. That is the only way I can describe the sound. Someone told me that it is just the way the engine runs. I think that it is a primer of some sort to aid the engine after start up and with the AC. Is there anyway I can get rid of this sound without hindering the engine? Does anybody else have the same thing or know anybody who does? I am going to get an exhaust soon and I am hoping to be able to start the engine and rev it up after without this sound rather than getting one to hide it.

 

Just a stab at it but is it the clutch fan. My 88 used to do that and it seemed more prevailent when it was cold than warm. I though the clutch was heat sensitive and that is what told it to engage. I know the clutch lets it disengauge the fans at highway speed to help with power when the air is not needed but I was never really sure exactly what the mechanism was.

I'm sure someone will kick in with a throrough explanation though.