I bought my 1998 XK8 4.0 with a kind of low, rumbling, grinding noise on idle… it’s quite irregular and only heard on idle or low speed. I was pleased when I found play in the tensioner idler, replaced the whole unit but the noise is still there.

it can be provoked most by turning the A/c on but also seems to be irritated by turning the wheel when stationary or turning on the defroster.

it sounds like dragging a heavy metal pipe along the floor.

im going to get a mechanic’s stethoscope tomorrow to narrow it down further but at the moment I’m leaning toward an A/C compressor problem. Although the A/C is working great in the Houston heat so far!

it also reminds me a lot of a noise I had on an old Saab 9-5 Aero that turned out to be the alternator… now that was a PITA to switch out… I’ve heard the XK8 version is also not easy…

so anyway, just thinking out aloud really, does this seem logical? I’ll get the stethoscope and see what that turns up!

I’m new here so I hope I’m not asking too many questions… I’m sure I’ll soon be able to answer a few as I start addressing the list of character quirks this Beauty has!

I would take the belt off. Turn evey pulley/ accessories by hand to see if one is making the noise. I would then start the car without the belt for only a minute, you don't want to overheat. If the noise is gone it is one of the pulleys/ accessories.

Ah yes sorry I should have mentioned, I did that when I replaced the tensioner... the tensioner pulley was the only part with play... the PS pump felt kind of notchy, not smooth to turn... so perhaps it's that?!

But if it is the PS pump... would the noise still be produced after turning on the A/C at idle?

Either scenario causes an increased loading on the accessory train.

Take a look at this thread from klynn - post #7 on:
https://www.jaguarforums.com/forum/x...0/#post2357472

I'd also replace the idler pulley by the alternator. Where the tensioner one has gone, this is sure to follow. Mine was 'grumbling' at 30K

My 1998's idler pulley went defective too. Made all kinds of interesting noises!

When tested, it was notched feeling when I turned it by hand.

John

Thanks! The idler pulley did feel pretty smooth when I had the belt off but I’d certainly prefer it if that were the culprit! I got a stethoscope so I’ll have a listen to everything this evening.

keeping my fingers crossed it’s not the a/c compressor… that looks like the hardest fix 🤞🤞🤞

i did check the pulley bolts on the PS pump pulley and they seemed fine also. But yeah the pump itself did not feel smooth…

Ok after probing with the stethoscope I’m pretty sure the power steering pump is making the noise.

it’s the only accessory on the belt that sounds rough up close and gets a lot worse when the wheel is turned.

so I guess a new pump is the best solution, and probably a reservoir… the fluid in there is pretty murky…

I got/had the grumble ..97/100K+ so I removed the roller by the alternator and cleaned the surface which was "dirty".
Put it back and no grumble ...I can only surmise that after 100k with pressure from one side that there is wear on one side of the centre race and I have put it back with the pressure on the previously unloaded side. Felt fine to spin ..felt greasy and through the stethoscope, it sounds fine. We will see. Now for that intermittent tick tick which is not a tappet

Thanks!
I did check the idler pulley and It seemed to be nice and smooth... I can see on the carfax it was changed a few years ago but I'll give it another look when I get the belt off again.

It's just a bit puzzling because everything seems to be working fine. A/C works. The steering may be a bit light but I've only had the car 2 weeks so I can't really compare!

And the sound is as embarrassing as worrying... If the car is idling without the A/C on it doesn't show up much. But as soon as either the A/C is turned on or the wheel turned at all, the clattering, scraping, grinding sound kicks-in until the motor is revved. I've been going crazy looking for loose things that are vibrating because that's what it sounds like.

I'll flush the PS system and give all the pulleys a good jiggling again before I start replacing the PS pump and reservoir, hopefully this weekend.

So I made a (long) video about all the things I've found wrong with the Cat so far...
This is the section where the grinding noise is covered.... I'm still thinking/hoping it's the PS pump... any other thoughts?!
Thanks!

Mine makes the same noise sometimes ...not when hot so I await your pump replacement.
Dependent on the milage the nikosil wears away so does not become an issue.
The revving on the highway is because the transmission has not gone into lock up. The fluid change may cure it but tell the guy doing it he will know if its a valve block problem. You can adjust the throw of the gear shifter so it does not hit the end and crack the plastic . Google XK8 To the garage. that guy can tell you how to do it . I see leather seat covers on UK ebay which would go in your suitcase.Thestrip is aftermarket and the silver thing on the door is to prevent dthe egde getting damaged ..you can get the them in green in the UK I thought I had problems but for only $2400 I can fix it I hope.
Keep us all posted.

Thanks this is very helpful!

I'll do the PS pump and top off the roof pump today or tomorrow so I'll update then.

I would love to have a go at doing the transmission fluid myself but most of my tools are still in CA and transmissions have always been a bit of a dark art to me lol But maybe I should learn.

You said you are not much of a mechanic so let me say behind the pulley on the air con pump is a clutch . the pulley runs on a bearing on the ac shaft but does not drive it until the electric clutch operates. You could have a bad bearing or a clutch in failure mode .
If someone can give us a diagram of the pump /clutch internals it may be possible to see if it can be dismantled in situ from the front. ie take the pulley off . .Of course, the magnet that operates the clutch is both very strong and stationary,has small radial clearance hence if the magnet had attracted any metallic particles they could touch the rotating parts and move as the magnet came on and off creating the variable grinding noise. Remember the old slogan TEST DONT GUESS ....
PS
just did a search on UK Google " replace air con clutch bearing " and there was a video and the parts cost peanuts.
PPS
This is useful from about 12 min in
look at this

Apart from the grinding, I can also hear a low-level 'clattering' noise when the motor is running. It definitely shouldn't be there as these motors run like sewing machines when they are on song.

I was wondering if the A/C compressor might be the problem, although I can only reconcile some of the symptoms to that being the root cause. But... it's only a thought and the compressor is a bear to R&R.

When is the noise audible? If the compressor is on, the clutch will be magnetically locked so the belt will turn the compressor. When the compressor is at rest the belt is running the compressor idler pulley which has has it's own bearing. if you hear the noise with the A/C off it is the idler bearing. If it's noisy with the compressor running the compressor is bad. A simple test.

if I can replace the clutch assembly with the unit in-Situ like that it would be amazing! I think I need to get under the car and take a proper look at the compressor… all my tools are 1500 miles away so I’ll pick up a Jack and some stands today thanks!

it really is a mystery… it reminds me of the noise my old saab made with a bad alternator bearing..

Hmmm… if the car is started without the A/C on it will not make the noise (perhaps a little)…

turning the A/C on will start the noise and it will continue to be heard at idle.

However turning the steering wheel at standstill or walking speed will provoke the noise, as will putting electrical drain on such as the rear defroster, regardless of A/C.

And the noise is not there with engine running without the belt fitted.

I replaced the tensioner already, the idler FELT smooth to turn but I might just switch that out anyway. The alternator pulley felt good and smooth, as did the waterpump and compressor (although I couldn’t get to that as easily so might be worth a second investigation).

the PS pump felt some resistance… not exactly rough and notchy but not smooth either. And it’s the only part that sounds a bit rough with a stethoscope so that’s what I’m hedging towards at the moment…

Increased load on the alternator also means increased load on the accessory belt, so that fits in with the other symptoms.

The stethoscope is a good way to localise these things.

If you do need to, you should be able to get the compressor pulley off in-situ - there's just an A/C line that may require some gentle adjustment to move out of the way. Depends on how far forward the pulley needs to come to clear the compressor shaft.

If you have a stethoscope it should be obvious which part is noisy. I've used just a length of hose to listen to belts, bearings and compressors for years and isolated and found the reason for many different sounds and failures. You are on the right path, search for the noise and isolate it. This will give you your answer. Good luck!