This is a weird one.
'03 XK8 convertible. 97k miles.

For about the last year it's had an intermittant noise from about 1500-2000 RPM. It's 100% engine speed related. It will do it in park or any gear.

The noise is hard to describe. It's like a "wooooo" or the sound of an old engine driven fan. It's not super loud. It's more just annoying.

I've been throwing parts at it for a while.

Things I've replaced to try to fix it:
- Power Steering fluid (3 times)
- Power Steering pump
- Water pump (twice)
- Idler and tensioner (3 times)
- Belt (3 times)
- Alternator

One time that I caught it doing it I quickly pulled the belt. It stopped. Ok, great. It's something on the front drive. Put the belt back on. Still gone - only to come back a few miles later.

I feel like I hear it best with the windows up.

As odd this sounds, I can't really pin its location down with the hood up. I've tried stethescopes, screwdrivers, hoses, etc to pin point the location. Nope.

Any help is much appriciated.

 

Probably not in the VIN range but info.

 

Thanks. That's a good thought. I do agree that my car is likely not in that VIN range (the one you posted is for 2002 XJs).

Once, it had been doing it more loudly on my way to a friends shop where I had planned to do a routine oil change. I did that, and after a bit, I drove home and it was gone. Of course, a bit later, it came back. I experimented with an oil additive (which claimed to reduce noise). No help. I typically use 5-30 Mobil-1 and Wix filters. I've wondered about going to a 10-40. But it's winter now and that feels like a bad idea.

Ont thing that's had me wondering is the water pump. I used the AC Delco one that's been mentioned here. But with it's different from OEM (shape of vanes and AL vs plastic) vane design, maybe it's a cavitation noise? The car never runs hot (even looking at the specific temp through an OBDII reader).

Also wondering if it could be something on the input side of the gearbox.

 

In any case , I would try using Mobil 1 0w-40. It’s a better oil than the 5w-30 and is still in the range recommended in our owners manual.

Z

 

Does it male any difference whether the engine is hot or cold?

Richard

 

I haven't found a pattern to it Hot, cold, etc. Ambient temp. Long into a drive or right from the start. It's done it and not done it at all of these times.

Why do you consider the Mobil-1 0-40 to be "better" than 5-30? I may try a different oil, just as another variable to try. But I dont see why an oil weight that's commonly used would produce this noise.

 

your own post suggested going to a 40 viscosity oil to see if that would mitigate the noise. But were concerned about a 10w-40 being inappropriate for wintertime.


j was only pointing out the existence of a Mobil 1 0w-40 which is a great oil, winter or summer. Furthermore, the anti-wear properties of the Mobil 1 0w-40 vs. a 5w-30 are well documented ( see the oil forums or Blackstone Labs)

a 5w-30 won’t “produce” a noise, but switching to a 0w-40 might quiet one .

Z

 

Thanks Z. That what I thought you meant. My next oil change is about 1k miles away. I'll certainly try it. But honestly, it feels like a very long shot.

Anyone else experience anything like this?

-Kyle

 

If you are still of the mind that the belt removal stopped it, have you repeated the test?
And then to do a control version of the experiment, just spend the same amount of time without removing the belt to see if time is the factor.
Could you offer us a video of the two conditions to capture the sound? Either from the driver's seat or under the hood.
Back in the day, the common oil was a 20-50. Anything over 60K miles would get a straight weight. But you aren't hearing rod knocks, so I wouldn't expect ANY sort of oil change to make your problem go away. Or put in a can of STP, the racer's edge? LOL!
You mention idler and tensioner. Does your belt have more than one idler?

 

Since the belt runs both the water pump and the alternator, you can't run the car for more than a few seconds without it. The point of my story was that given how intermittant this is, the belt test is inconclusive (unless it somehow makes the noise when the belt is off). But honestly, I'm tired of randomly chasing this. I'm happy to work on things with a real chance of diagnosing this or fixing it. But no more darts in the dark.

I've tried to get a video, but the sound doesn't represent the real noise well. Thanks.

Like most cars, XK8s have both an idler and a tensioner. Both have been replaced, more than once. The only things on the front belt that haven't been replaced are the AC compressor and the crankshaft. I'll get a new car before I replace either. lol

 

Sometimes a vacuum leak will make strange noises like that...

 

Has piston slap beeen rules out ? Sorry if this has been mentioned already.

my car has a wicked piston slap racket when cold. It goes away completely at 160-170 F coolant temperature.

Z

 

Here is an easy thing to do. Have you turned the AC ON or OFF when the noise appears? AC clutch is what I am beginning to suspect here. Also possibly the AC compressor itself, but either way, it's easy to do the testing.