I have a 93 F350 M diesel, 300,000 + miles.

I've noticed that sometimes when I press down on the accelerator I hear a
destinctive high pitched whine or whistle. This is NOT a turbo, nor does it
have a blower. I've had this truck for over 5 years now with no major
problems. After a while the sound goes away. The belt is only about a year
old. any ideas?

thanks

 

Check all your pulleys on the sepentine belt drive for bearing wear. Many of the smaller pulleys need replacement, especially at the milage you are at.

Check you water pump bearing for play.

Check you altinator bearing for play.

Can you hear the whin and whistle when you rev the engine while you are under the hood?

Do you have AC on the truck. The AC clutch and clutch bearing wear out and can make all kinds of funny noises as they get too much play in it.

Seb....

 

Thanks for response.
The altenator is relatively new (replaced original one 2 years ago)

It makes the whistling sound at times even with the A/C off.

How do I check the "play" in the pulleys ? How much "play" should there be ?

.000, .050 ?

Thanks

 

The AC clutch will be noisy especially when it is off not on. If you AC still works turn it on to see if the noise will go away. Mine in my 91' F350 needs a charge and the clutch has been very noise for some time.

All the little idler pulleys should be tight, no play. They should turn freely with a tiny bid of drag. Water Pump Bearing should be tight.

How many miles since you changed the belt. I consider myself lucky to get 30k before my belt starts to whin and make noise.

Seb...

 

Well the belt probably has about 8000 miles on it.

will diesel waterpumps start "weeping" i.e. drip coolant when the bearings
are going out? like gas engine waterpumps do?

I will check the pulleys for "play"

The only sound I hear from the A/C is the compressor clutch engaging/dis-engaging when the A/C is on.

Like I said ... sometimes I hear this whistling whenever I accelerate, but not
all the time. and after a while it goes away ...perhaps once the engine
is good and hot whatever's making the sound has expanded and there's no
more play or slack...

Thanks

 

Yes, there is a weep hole near the bottom of the water pump housing.

If the noise stays the same when you put the AC in and out than that is most likely not it.

Altinator is new so that can't be it.

Check the small tensioner and idler pullies for play. Also check the tensioner make sure the bushing is not worn out on it. When you look at the small pulleys they should align perfectly. If the bushing on the tensioner is worn the tensioner belt tends to go out of alignment with the other pulleys. The belt should be parallel to the tensioner pulley.

Belt at 8k should be still ok.

Sometimes these noises come and go. If they don't go away you will find the problem sooner than later.

Last thought, given you got 300k on the engine, check the bearing on the power steering pump. They do wear out.
Seb....