Long story short, the thermostat blew on my 98 XJR a few weeks ago. I managed to get home by constantly stopping and starting the car on route and letting it cool down. On the first occasion I lost some coolant. I refilled it at a friends place 200 yards down the road and luckily I had my OBD scanner with me and was able to monitor the coolant temp.

Anyway, I've installed the thermostat and now the car is perfect again coolant wise, however once it's warmed up there is an engine tap. It sounds like it's coming from the top half of the engine on the right hand bank (not sure if it's bank 1 or 2, but it's the right hand side of the engine if you were sitting in the drivers seat) about 12 inches from the rear of the engine.

The facts are as follows...

• It only starts after the car has warmed up. I suspect this is a major clue.
• It's not a heavy noise and it's loud enough to hear outside the car, but inside with the doors closed it's only just audible.
• It makes the car sounds a bit like a diesel.
• I'm not convinced it's a timing chain tensioner issue due to it's location, unless the sound is travelling. This is something I plan to check anyway as I can't tell you if the tensioners have been updated already.
• I'm not sure it's VVT related either. It's not a ticking but somewhere between a knock and a tick and it sounds quite "light" if that makes sense.
• It is rev related, but the higher the revs the quieter it gets. Could be the engine noise drowning it out.

Any idea where to start? If I can't figure this out it's going to be an expensive trip to TL Jaguar. I'm competent to have a go myself, but striping down the engine at home and investigating is something I'd rather not try.

 

At the worst end of the spectrum ... it is pointing at rod knock. In other words, a big end bearing got wiped out due to overheating.

This is based on the description that it is towards the middle, sounds like a diesel, is temperature dependent and speed dependent.

XJR's do not have VVT.

 

A possibility is that a valve seat dropped just a little (from the engine overtemp) and now the tappet lash is increased. You could check ALL the valves for proper cam-to-tappet clearance when you pull the cam cover to check on the tensioners.

You might also have had the secondary tensioner plastic 'foot' that rides on the chain get hot and fall off, resulting in increased chain slap but that is noise at the front of the engine.

bob gauff

 

Thanks for correcting me on the VVT. I didn't know that.

Oh dear! I hope you're wrong on that for the sake of my wallet.

Listening to some of the rod knock videos floating about the noise is similar but nowhere near as severe. Also it sounds like it's top end rather than bottom end.

I'll get a video up on youtube and post the link. You guys on the forum need to hear it I think, but it's gone 10pm here in the UK so will have to wait until tomorrow.

 

This is something I was wondering about. Would also fit the profile of the kind of noise I'm hearing.

On the basis it is this and the valve clearance is out, whats the course of action? Head off, re shim and valve grinding?

 

I also have a new noise which seems to be coming from the Supercharger. It starts as soon as it turns on and seems to diminish as time goes on but it is still there the entire time. I am not sure how hot the car got but it never blew steam or dumped coolant just the fans came on full bore and ran for five minutes after shutting it down. The noise started right after that problem (tstat) was resolved. It is not a clicking noise so much as it is a muted rattle. I don't think it goes away at speed it just gets drowned out. It is much louder when I put my ear to either side of the SC (the bank that says supercharged on it).
There are no warning lights coming on. The car runs strong. It may be that there is not enough coolant in the SC but I would think it would be up there by now. I did not open the port at the top of the SC when I refilled the cooling system.





2002 Super 8 104k supecharged Vanden Plas

 

You do need to bleed the coolant from the plug on the intercooler.

 

crap........do you know what size that is?

 

You can also break a interccoler fluid line if you don't have the big hex wrench. Just open one of the small lines and "massage" the pump inlet tube until water is gurgling out of the intercooler line, all while keeping the expansion tank full to the top. Gravity works, if you give the air an escape route!
BTW, I bet you find it is already full by now.

 

You just need a short bolt with the right size head and two nuts to jam together on the bolt. Turn with a wrench or socket.

 

That rattle might be the SC drive coupler. There are repair kits available in ebay or elsewhere. The overheat might have tightened up your rotor clearances and stressed the coupler. If that is the problem, then the repair is in the realm of DIY and not terribly expensive.

 

I found a spark plug socket that fitted perfectly. You know, the kind with one end that has a hex molding for a spanner. And I believe that jaguar states you shouldn't have both the supercharger hex nut and expansion tank open at the same time.

Procedure is to fill the expansion tank whilst massaging the rad hoses to release the air bubbles. Once the fluid level stabilizes, turn on the ignition. The supercharger waterpump will run. Leave the ignition on for at least 2 minutes. Turn off the ignition. Top up the expansion tank. Turn on the ignition. Wait 2 minutes. Turn off the ignition. Check the expansion tank level. Replace the expansion tank cap. Open the supercharger hex. Top up the supercharger level. Replace the supercharger hex. Check the coolant level. Run the car up to temperature with the heater on full until the fans kick in. Allow to cool. Check the coolant level.

Correct me if I'm wrong anyone, but I think this is right.

I also suggest you remove the supercharger belt after you've done this and run the car. This would confirm if the noise is supercharger related or not.

Back to my issue, the noise is 100% a top end noise. Coming from under or around the intercooler. If I put my hand on the intercooler it dampens the noise a little. Nothing seems loose. I've got a video I'll upload tomorrow. Mine is definitely not a supercharger noise. The belt has been removed. Also the noise only starts after the auto choke has phased out and the normal idle speed has leveled out. It doesnt do it from cold. I'm wondering if a valve shim has worn out when the car overheated?

I've also ordered a bore camera so I'll have a better idea by mid week.

 

Bondy, I'd be inclined to agree with Bob, check the valve clearance on the noisy side, have you used a stethoscope-long screwdriver to locate the tap?

These engines drop valve seats on overheat events - so a replacement cylinder head is way cheaper than remedial work on the original - checking flatness after stripdown, rebuilding with new seat cut and valves re-shimmed is very time consuming and if not doing it yourself gets expensive quickly.

 

The reason the procedure says to not open the expansion and intercooler caps at the same time is that the coolant will run from the tank out through the intercooler cap, proving that the supercharger loop fills without a lot of extra effort.

 

You can also break a interccoler fluid line if you don't have the big hex wrench. Just open one of the small lines and "massage" the pump inlet tube until water is gurgling out of the intercooler line, all while keeping the expansion tank full to the top. Gravity works, if you give the air an escape route!
BTW, I bet you find it is already full by now.

Sparkenzap,
Do I have the expansion tank open or closed during this procedure? Which is the pump inlet tube and do I do this on both sides?





2002 Super 8 104k

 

Ok. The youtube link is


The noise sounds "heavier" on the video than in person. It's the "clack" noise I'm referring to. I have a bore camera arriving tomorrow so I'll pull the plugs on that bank and check visually before I start removing the head. I'm not convinced it's something serious yet. I'll check the compression whilst I'm at it.

On further inspection it does appear to be coming from below the "E" on the charge cooler. I've tried the screwdriver method (well a metal rod actually). I may have to get hold of a proper stethoscope. If you place the rod against the block it's as smooth as silk. No noise is detected by ear when you're below the engine. Still open to ideas. The video is only 10 seconds long so have a listen.

 

after you turn the car off does it still make that 'clack' noise or do you only notice it when the engine is running?

 

I am thinking valve noise as well. Easy enough to pull the cover on the offending side and check clearances. You can change the shims in situ, but its a bit of a pain.

 

First let me say: I have no personal experience with an XJR.

I do however have experience with vehicles overheating. The one thing that I didn't read in this thread that I am looking for is that the oil has been changed since it got too hot. Anytime a car overheats, the first thing that should be done is replace the oil (and coolant if it is at all suspect). If the oil is burnt it will not lubricate and will leave muck all over every surface and passage way of the engine.

I've managed to salvage more than one over heated engine (Toyota Supra and AMC Strait 6) with an immediate oil/filter change with a heavy detergent oil (Rotella T5 or T6 "Deisel" oil for example) and another oil/filter within 1000 miles with the regular oil i always use in the vehicle.

This may/may not eliminate the noise, but I think its a must if there is any question about the condition of the oil. And if it got hot enough to damage metal parts, you can just about bet the oil is burnt.

Good luck.

 

Have you tried running the engine with the supercharger belt disconnected...?