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My 2001 F150 with 255xxx miles has a squeaking under the hood. It is only present while the throttle is pressed while driving. It is loud enough to be heard in the cab, but not over the radio. It changes with engine RPM. It will not squeak while in neutral at any engine RPM. As soon as you lift your foot while driving it vanishes. Turning the A/C on/off doesn't change anything. The engine is a 4.6L V8 with the 4 speed automatic transmission, all original components as far as I know. The serpentine belt is brand new. No drivability problems, no CEL, with a mode 6 scan tool I do get a code for the EGR being open too much.

The squeak is never there on a cold engine. If it is under <50 F outside it never squeaks no matter what the engine temp is. If the ambient temp is > 50 F it starts making the noise once the engine temp gauge moves to the normal range. I've looked under the hood while idling and the none of the pulleys are wobbling and the tensioner doesn't jump when you open the throttle.

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    With everything you are describing, I'd be looking towards the power steering pump first. You are describing a "squeaking" ... if it is more of a whining noise, this is what I'd say. Your squeak may be my whine ;-) – Pᴀᴜʟsᴛᴇʀ2♦ Mar 1 '14 at 19:03
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    Actually, its more like a chirp-chirp-chirp-chirp. – Eric Urban Mar 1 '14 at 19:12
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    Are you seeing any seepage out of the water pump "pee hole"? (Antifreeze puddle or having to "top off" over time.) – Pᴀᴜʟsᴛᴇʀ2♦ Mar 1 '14 at 19:32
  • You can't look in the radiator to check the level(no cap), but the coolant bottle on this truck has been at the same level for the past six months. There is no obvious indication of leakage around the waterpump. – Eric Urban Mar 1 '14 at 19:37
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    Does it make the noise at a stop when you have your foot on the brakes, in drive, and you press on the gas a little (not enough to break the rear tires lose, obviously)? – Pᴀᴜʟsᴛᴇʀ2♦ Mar 1 '14 at 19:50
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I figured it out today. The spark plug in one of the cylinders blew out of the head while driving. The 'squeaking' was actually a whistling as air was pushed passed the spark plug.

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Can it be the fan belt. It probably becomes loose and slips as it heats up? When cold it is tight enough to not slip.

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  • I would doubt this is the issue. First, he has a new belt, which is less prone to squeaking. Second, as the rubber compound in the belt warms up, it becomes more pliable (or sticky) and less prone to squeak. – Pᴀᴜʟsᴛᴇʀ2♦ Mar 1 '14 at 19:30
  • Unless whoever installed the belt did not tension it enough. – Mohinder Mar 3 '14 at 5:52
  • This vehicle has a serpentine belt with a tensioner which is self adjusting. But still, belts don't stretch when they become warm. If belts are going to squeal, they will most likely do it when cold, then stop when warmed up. If they are going to squeal when warm, it will be continual no matter what the temperature of the belt is. – Pᴀᴜʟsᴛᴇʀ2♦ Mar 3 '14 at 14:26

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