Strange Sound On Start-Up....

[MobyDick]

Sometimes when it is cold out, and almost always when it is really hot outside, I get this odd sound like the engine is revving high when I first accelerate - only lasts a few hundred yards. But the revs are normal. Sounds a bit like a drastic air intake for a few seconds then it settles down.

Any ideas what that may be.

 

[GRIP]

alittle more info on the truck please year and model but it might be the fan till the fan culch kicks off.

 

[Grasshopper]

That's normal. I don't know specifically what it is, but I think GRIP may be right.

 

[MobyDick]

It is a 2004 5.4 liter with 55,000 miles. Come to think of it, I have noticed this sound at low speed when it is really hot out and I am in stop-and-go driving. Disappears when I speed up. Does not explain why it would come on when the engine is cold, despite a high ambient temperature. The sound also increase a bit with engine speed.

 

[green03]

The fan clutch gets "stiff" when cold and will engage first thing in the morning just like it does in traffic when it is hot out. It uses a silicone fluid inside to grip so it acts the same when it is very cold out as it does when it activates when hot.