I have a '77 F-150 with a 300 inline 6 4 speed tranny. Motor rebuilt by previous owner 35,000 miles ago. Runs fine, no valve train noise, no knocks, clunks, etc. Oil pressure fine cold, drops to about 10psi when warm at idle. 10w30 oil, just changed. New alternator, water pump. Belts look fine, but they are older. Getting a loud high pitched whistle from the front area of motor. When cold, I start it, everything's fine. When I start driving, the whistle starts, until I step on the gas increasing engine rpm's then it stops, I let off the gas it comes back. I push in and out on the clutch pedal while moving, no difference, noise only changes with engine rpm. I sit at a light and the noise is still there. Still changes with engine rpm. Doesn't matter clutch in or out. Doesn't matter what gear. Park the truck leaving it idle, noise continues for about 15 to 20 minutes, then stops by itself. Until I shut it off. When I restart, it doesn't come back. Until I drive it again. What the hell's going on? Am I an idiot and I just need new belts? Is my motor about to blow up?

 

waterpump could do this

John

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

It's a new water pump. I put it in because I also thought that was where the noise was coming from.

 

A flex-fan can sometimes cause a noise like that is you have one.

 

I had an old Triumph sports car once that I damaged the front alternator bearing when I installed it. It had a bad whistle at 2200 rpm, with lower level harmonics at 1100, 3300 and 4400 rpm. The bearings in Ford alternators are much easier to change ( and relatively cheap ), so you may want to check this.

 

I'd change belts. When the engine's cold they won't start squealing until they get hot.

Trail Rider

 

It seems the more I drive it, the more it sounds like an air whistle. Also it seems directly related to gas pedal position. Like when I hit the gas, vacuum changes in the motor and noise goes away, when I let off the gas, it changes again and noise comes back. You know how when you leave your window open a little, you hear that whistle? That's what it sounds like only ear splitting loud. I don't think I damaged the alternator bearings when I put in the new one, but I'll check it. It doesn't seem to be fan related, as it's not a clutch fan, it and the pulleys are bolted directly to the water pump. One more thing, I'm not sure if it's related, but, this noise seems to have started right after my thermostat stuck open. I'm currently running it without one, 'cause when I did the water pump,I broke the housing, got a new housing and thermostat,and couldn't get it to stop leaking with the thermostat installed. I put in the stat as follows. I stuck the gasket to the cleaned head with rtv, installed the stat with bridge side into the housing, spring side into the head, and bolted it all up. It acted like it was stuck closed. Got no heat, but temp guage went to hot. It was the opposite when it was stuck open. This one's got me puzzled. I'm installing new belts today.

 

 

HEY, try removing the belt, start the truck and if you hear it then you know it isn't the belt,pump,alt so forth. spray some paint on the crankpulley while it is running with hte belt on and see if it affects it. if it does then you know a little more.