strange engine noise??

[Sweeper]

2000 Mustang 3.8L V6, 34,000 miles. Engine starts an irratic tapping/rattling noise when engine is warmed up. Had it looked at yesterday at a shop. They pulled the belt off and the noise goes away? Put the belt back on and the noise comes back. Also, it only starts to tap when the engine is at warmed up or at optimal engine temp. The guy said it was coming from the water pump and that he had never heard a noise like that before from a pump. But he was positive on the area of the noise. I asked him if he thought it might be coming from the timing chain (since it sits right behind the pump) and he said that he listened to both the timing chain housing and the pump and it was defenitly the pump. Plus he stated that at 30,000 miles he has never had to replace a timing chain, esp. since I have had my oil changed every 3,000 miles since I bought it new. He also said it wasn't anything internal like a valve or lifter noise. Anyone else ever had this problem? I took the car home (didn't have it fixed) and of course by the time I got it home it was warm and ticking/tapping etc. So I pull the belt off and the noise quits. I drove the car around the block without the belt, no noise. Put the belt back on, drive around the block again and the noise is right back. Could a water pump rattle and tap like that? The tapping is also not a steady tap either. Very strange?????????? First time I have ever heard a water pump tap/rattle. Any other Techs. have any suggestions.? BTW: When I stated they and I pulled the "BELT" off, it only has one belt (serpentine) that runs everything, which makes it difficult to diagnose which pulley is making the noise....

Sweeper

[hifi]

The water pump is definately a possibility. Whenever I have an issue I am suspecting as a pulley, (Generally the idler pulley is the one that goes first) I have gotton into the habit (very messy though, so if you do it, do it outside) of spraying WD-40 on each individual pulley (one at a time) to see if the noise will subside. If anything, it should make a variation in the noise, therefore helping you to identify the suspect......

[Cruez]

Could be the water pump bearing. At 30,000 miles it could just be a fluke with that waterpump.

But an Idler pulley like hifi said is more suspect.

The belt is heating up, expanding, and bouncing off the plastic shroud. Well, at least I'll bet that's what it is. That was big problem they had with the Contour zTec 4 cylinders. They didn't leave enough room between the belt and the plastic cover. When the belts loosen up from use, and then expand from the heat, they tend to flap around a little bit. So, it might be the water pump, but it's probably something that simple. Try driving around with just the shroud off and see what happens. I like to be wrong (though in this case I'd be saving you a couple bucks by being right. ).

-Whir

[caddmannq]

I'm thinking Whir is right on here. If you watch the belt as you goose the throttle a bit, you'll see that the belt does indeed jump or flap a bit.

It couldn't be the timing chain, as removing the belt would not stop timing chain noise.

It could be the water pump itself. I've seen waterpumps that rattle because the impeller inside the pump has cracked or come loose from the shaft. That's not likely though.

[draboo]

on some water pumps(gm v8 in particular)there is a small hole in the water pump housing. keep an eye on that hole,cause when the bearing (or bushing,whichever it is) goes south,coolant will leak through that hole. definate indication of a shot water pump.

[Sweeper]

replaced pump today... still has noise. checked the alternator, idler, tensioner, A/C, powersteering..they all seem fine. Lost....
There is no shroud. Electric fan. Serpentine belt. NEW BELT...
ya know draboo I feel like your avatar

No shroud you say? Evidently they don't package them the same way they do in the Taurus and Sable then, because they have a serpentine belt shroud. Ah well, you win some, you lose some.

-Whir

[caddmannq]

OK, this is what you do:

Get a piece of 3/8" rubber hose about 2 feet long.
Get the car warm & park it in the driveway.
Stick one end of the hose in your best ear. plug the other ear with cotton, a cigar butt, whatever.

Listen thru the hose while you move the open end around close to all the accessory pullies & bearings, also the A/C clutch, idler spring, and alternator brushes and fan.

At each point, have an assistant goose the throttle lightly, and listen for a change in the sound.

Also, listen around the thermostat housing, and radiator. Something may be floating around in there. There might be a chunk of casting flash rattling around in the cooling system also.
But the noises from sush a deal wouldn't be very loud. Can you hear this when the hood's closed? From the driver's seat? While driving? or just idling? Does it change with RPM? or just with temperature?

PS: After you find the bad accessory, go back to the guy that sold you the new water pump and slap him around with the rubber hose until he fixes what's really wrong.

[Sweeper]

to be honest I'm beginning to think it's in the valve train even though the sound goes away without the belt. Without the belt the engine isn't under as much load.