Hello,
First time poster here. I'm attempting to help my father sell his 1998 Jaguar XJ8 Van Plas (V8 4.0L VIN: 842068) and running into some mysteries.

The car had overheated 3 times - once to the point of stalling (due to a blocked fan). That was repaired and seemingly solved the overheating problem, but now there is a new complication...

After casual, city street driving for about 30 minutes - the car will begin making a rattling sound. This continues to get louder until the car finally stalls. This happened once. Upon second test drive, the car again started rattling around the 30 minute mark and I pulled over before it could stall again. Since then, I've driven it 20 minutes, to a mechanic, without the rattling.

The mechanic is saying this is due to the timing chain tensioners and is recommending we replace the entire kit (parts and labor = $2000).

However, the more I research, the more it sounds like an issue with the catalytic converter.
If it were the timing chain tensioners - wouldn't it make the sound right at start up?
When a rattle kicks in after 30 minutes - is that more commonly a problem with the catalytic converter?

Any and all input much appreciated!

 

What I understand is that warn chain tensioners cause the rattle on start-up because the chain is too slack when the engine starts up.

Is it not possible to tell if the rattle is coming from the catalytic converter?

 

The most important question is how many miles on the car? And have the tensioners been changed?

If not then you better plan on it before they let go and you destroy the engine. Remember on the early 4.0L V-8's they will fail it's just a matter of time.

It's easy to check if the cat is blocked and your mechanic should be able to do it in less than 30 minutes.
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Thanks kbeachy,

Everything sounds fine upon on start-up, the rattle only begins after about 30 minutes of driving.
Once the car cools back down, the rattle is gone - it doesn't begin at start-up.
So do the tensioners have to be warm before the rattle begins?
Would tensioners eventually cause a car to stall?
Because with this particular rattle, if it continues for about 5 minutes, the car dies.
Does that sound more indicative for a catalytic converter?

 

It's hard to say but the cat is easy to check and eliminate as a cause. So do that first and see what happens.

The most common symptom is rattling at start up but that also depends on how bad the wear is and are the primary or secondary tensioners in worse shape? It's normally the secondary ones that let go but this is not written in stone.

You can visually check the tensioners too by pulling a cam cover and look for broken plastic but this is more work than checking for a plugged cat.

And I think we need to understand that's when you hear the rattling but that does not mean it was not rattling before and you just can't hear it. It all depends on how bad things are and if anything has let go or is it just sloppy.
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All useful information, but you may get more info on the X308 forum, the one for your particular car.

Yes, rattling after 30 mins does not sound like camchain tensioners, although they are likely to be about to fail if never replaced. It sounds like warm-up is loosening something up due to expansion, so could be exhaust/catalyst related.

 

The engine overheating is liable to damage the tensioners and accelerate failure, but the rattle occurs on startup, when the tensioners have no oil due to cracks. They have a valve to prevent loss of oil, normally.
Your problem does sound like cats or something else.

 

Thanks for the input everyone!
I'll checklist all of your suggestions when I'm with the car tomorrow.

In the meantime - quick show of hands - in your opinion, which is more likely to cause the car to stall after 30min of driving...

A. Tensioners
or
B. Catalytic Converter

Just want to gauge the general consensus of the board, on the issue of stalling.

Many thanks!

 

B, B, and B. You diagnosed the fact that the rattle and the stalling are related. If it was the tensioners, Yes, the rattle MIGHT get more pronounced after the oil thins, BUT if the timing has jumped, causing stalling, that does not return to normal as the engine cools. If it jumped, it stays jumped.
BTW, In my anything but humble opinion, following advice for what is wrong with YOUR car in YOUR situation by vote is pretty risky/.

 

Sounds to me like the cat conv, but that is certainly not a reason to not follow through with the chain tensioners issue. When I was researching which year XJ8 to buy, I heard such horror stories about the chain tensioner problems (even failing after 40,000 miles) that I didn't want to even risk buying used because it would be hard to know whether I was inheriting an unfixed problem. (Besides, I like the innovations on the 2004 model anyway.)

If the chain tensioners have never been replaced and it has some miles on it, the problem needs to be addressed. Then again, if there are no symptoms it would be frugal economically to pass on the risk to the purchaser if your father's trying to sell (cause it ain't cheap to repair!). Chain tensioner failure will more than likely be catastrophic to the engine, from what I've read.

So my advice is decide whether the cat conv needs to be replaced and go from there. But do it quickly because risking bad chain tensioners is high stakes.

 

kbeachy:
I concur with your basic premise, but the immediate problem should be diagnosed before launching into the tensioners, since it MIGHT involve something internal to the engine,

That said, if you DIY, the chain tensioner repair will possibly make the sale easier, and certainly help your conscience if you sell the car to a friend or acquaintance.

 

IMHO $2000 for a job where a full set of parts costs circa $300-$400? seems excessive - I guessed the doller price - I'm in the UK and did a quick conversion.. if you can do it yourself its probably worth doing, especially if high mileage and they haven't been done before.....I think it less likely that this is the source of the rattle after 30 mins though - everything I have read seems to say that 'rattle on start up', not later like your rattle, suspect cam chain tensioners/chain wear.... Hope this helps.

 

Overheating does a lot of bad things. The 1998 does not have steel sleeves in the cylinders, they are nikasil plated. Overheating destroys this. If the head gasket is
leaking, there will be coolant and white smoke in the exhaust. Did that occur during
the 3 overheat episodes? I am not sure exactly where you should go. I would suggest
replacing the engine with a junk yard engine with warranty, but you will end up spending more than the car is worth. 97 XK8 engines will work. 98 XJ8 engines work, but newer ones won't due to computer, variable valve timing issues etc. You can find
a replacement engine for $2,600 with the tensioners done.

 

Thanks Lear45,
That's what we're facing now - how to get rid of the car . I should probably just put it up for sale as a fixer-upper. Today I took the car to a second mechanic who said the rattling was from the chain due to thinning oil (from overheating) and the stalling was due to a sensor (or something) involved in the thermostat housing (couldn't fully understand his english over the phone). Is there something connected with the thermostat that will stall a car before it overheats? The needle never passes midway.

 

The temperature goes from mid range to pegged hot instantly. Think of it
as more of an idiot light than a true temperature gauge.
I overheated mine stuck in traffic on the interstate. A cement wall on one side and no shoulder on the other. I spent $2,650 plus installation for a used motor. Not worth it unless you love the car. The local junk yard offered me $300. Coventry West said they would give me more if I delivered the car to them. At best you might get $1,000 for a non running car. Wish I had better news. I have put $8,000 into a $3,000 car. I really like driving it though.

This would make a great parts car if you replace it with a running car....
or one with a bad transmission.

 

The only sensor I know of in the thermostat assembly is the engine coolant sensor. I had bad sensors in my 2 Saturns that caused them to idle wrong--much too fast. So that sensor can affect idle and, I suppose, cause stalling too. Replacing the sensor by itself is possible, or you can replace the entire thermostat assembly. It's possible as a DIYer without a whole lot of experience and expense.

So are you going to check out the catalytic converter as the source of the rattle or just assume it's related to the chain? Or maybe I missed something.

 

The knock sensors are attached to the thermostat tower, but I'm not sure if that would cause misfires. If the cat converter is blocked, that could cause poor running. I would try to get it running decent before trying to sell it. Like others have said, it isn't worth much in a non-running condition. I guess it depends on how much it will cost to fix. Have you got a code reader ? The knock sensors will set a code and give you restricted perf.

 

For future reference if someone else experiences these problems...here's where my car is at to the best of my (very limited) knowledge...

The "rattling" was most likely the timing chains. My oil had degraded from previous overheating, and once the car heated up after 30 minutes, it began producing a cranking sound due to bad oil continuing to thin out from the heat. The tensioners seem to be ok for now, but will have to be replaced soon because they are bound to eventually fail.

The stalling was due to overheating / a failed coolant temperature sensor. The hoses are in bad shape and the entire thermostat housing structure should be replaced.

(I'm still trying to figure out if I should just replace the sensor myself and sell the car, with a warning to the buyer that the tensioners and thermo housing/hoses will need to be replaced soon)

Many thanks to everyone on the board for all your input - y'all are lifesavers.
I hope this thread helps someone else down the road.
Here are some links regarding thermostat housing replacement....

STEP BY STEP THERMOSTAT HOUSING REMOVAL WITH PIX!
JagRepair.com - Jaguar Repair Information Resource

https://www.jaguarforums.com/forum/x...acement-97123/

The first thread is leak from thermostat top - last posting 5/19/2010:
leak from thermostat top

This other thread is Thermostat Housing Leak...Help! - last posting 4/21/2011
Jaguar Forums - Jaguar Enthusiasts Forum - Powered by vBulletin

Torque Specs
https://www.jaguarforums.com/forum/x...ue-specs-5621/

- Jim Lombardi

I just finished replacing the Thermostat housing on my 98 xj8, I followed the recomdations I found in here on bending an 8mm wrench I did things a little differently as I bent it so I had the box end to use on the bolt. Also I found a screwdriver whose blade fit the open end of same wrench that gave me the leverage needed to break the bolt free then it was just a fiddly job of removing the bolts, I hope this tip might make it a little easier for the next poor guy to rebuild his cooling system.

 

Zip tie method for the tensioners+thermostat housing+sensor=
8 hours under the hood and about $350. Pay a mechanic and well, the price goes up.

None of this is out of the reach of the average Joe if you follow instructions that can be found here on the forum.

 

My advice is to replace the thermostat housing assembly/tower yourself, which comes with a new engine coolant sensor. It's a very do-able job in a couple hours. Depending on the mileage, what you initially paid and think you could sell it for, and if the chains have stopped making the rattling sound, I'd try to sell the car without replacing the chains and the tensioners--with disclosure to the buyer. Anyone who knows anything about Jags or has done his homework should realize that buying this model used will very likely mean dealing with the tensioner issue.

The other option is to pay for replacing the tensioners/chains and trying to recoup the cost in the selling price, but I think you'll take a bath on that one unless you can do the work yourself.