I have a 2000 XK8 still with the original plastic thermostat housing. The car has 44,000 miles on the clock and I have replaced the upper tensioners. I'm not looking forward to replacing the thermostat housing. In fact it is not obvious to me as to how the original hose clamps are removed. My question is, do these always fail? the car is driven very modestly. My wife and I both drive it and don't consider it a high performance race car. Just a beautiful fun car to drive around the ranch.

Your comments regarding the need to replace this thing will be appreciated.

EZDriver 95 XJ6 2000 XK8

 

Good day to you:

If you search around there is pretty much a step by step guide to doing the housing. I believe there is a screw or bolt that requires bending a wrench. And then you could change out your coolant etc while you are at it. Mine is new but was done before I bought the car as well as the water pump which they recommend changing as well. But in regards to your question some suggest and I tend to agree that its not so much the use as the age of the housing etc. I find the plastic on these Jags pretty cheap and tends to get brittle with age caused by heat from the engine. Personally I would change it since you have to be pretty fast of the mark catching an overheating engine. Its just one of those peace of mind things. It may be ok for a long time. Or it may fail.

Howard

 

On my two cars the thermostat housing has been replaced on each once under warranty and I replaced one moving to aluminum after a second leak. Pretty good chance that yours is going to fail at some time. Fortunately, the failure is a soft one, slowly showing crusty yellow/orange around the base without catastrophic coolant leaks. That fits well with my philosophy of not fixing anything that is not broke.

 

My 99 XK8 engine appears to be completely original @ 59K miles, except for a hole in the insulation above the thermostat housing. Yes, they replaced it with another plastic housing.

I've got to pull a valve cover to inspect the secondary tensioners, and will be installing a new metal thermostat housing, new thermostat and new metal impeller water pump. Changing the thermostat housing is well documented in this forum--and is not really too bad of a job.

Another way to get the two back bolts out on the thermostat housing is by using a metric crowsfoot open end wrench head--available @ Harbor Freight.

Good luck!

 

If you wish to replace the housing (and I recommend that you consider it) I have instructions on my page at Jaguar thermostat housing 4.0 xk8 I hope this helps!

 

Gus has a good website - I used it to replace my thermostat and have some additional comments in my post on the replacement. The hose clamps come off by pinching the clamp with a pair of pliers gently and easing them off the hose.
Definitely there are lots of plastic items around the coolant system including clips that you have to release carefully otherwise they will break. A dreary job but not difficult - as others have pointed out, need a crows foot wrench to reach the back screws.

 

I agree that the failure is usually a soft one, slowly showing crusty yellow/orange around the base without catastrophic coolant leaks. Mine was even more subtle. I kept noticing the coolant level was falling after every drive but no coolant leaking on the garage floor. That was a head scratcher for sure. It turns out that there was slow leak at the base of the thermostat tower. The leak only started when the engine was hot and the pressure built up. It would then slowly leak on top of the engine and fall onto the hot manifold in the rear where it would evaporate and dissipate. Keep an eye on the coolant level!
The other thing I can add from my experience is that I decided to just replace the gasket as that was where the leak was coming from. At the same time for convenience I swapped out the thermostat and seal. Well, that solved one leak. However, because the tower is plastic, old and brittle, all the wear and tear of removing it actually warped it a little and the screws on the thermostat cover became stripped. I ended up doing it a second time with the aluminum housing.
When, not if, you decide to tackle the job, the bent wrench was the only thing that worked for me. And, don't forget to use the correct coolant.

 

And your waterpump should be okay on a 2000; the early ones were a problem. I replaced mine while doing the t-housing changeover and the old one was fine, no broken pieces. If it's noisy or leaking, then time to replace it.

 

Thanks guys. Lots of good info and I appreciate all the input. Will probably do the job this spring along with changing the coolant again.

EZDriver

 

I just had mine replaced by Jaguar. 2000 XJ8. Mine did have a catastrophic failure. See my post. "Suspicious Thermostat failure"

I notice they replaced the Jaguar unique hose clamps with the old style worm gear ones. Jaguar service advisor said these hold pressure better & the original Jaguar ones are not supposed to be reused! Well, not knowing that when I changed my thermostat 7.5 years ago, I reused them. So, follow the excellent instructions by Gus & use regular replacement hose clamps.

 

So, are you saying that the clamps you re-used 7.5 years ago are still installed and functioning correctly? Then why change them? They're known as 'constant tension' clamps and as long as they haven't broken or been destroyed by mishandling they should actually be more reliable than any style of worm clamp. As hoses age and shrink a worm clamp beomes loose, a constant tension clamp's spring action coninues to apply the same pressure (or close to it.)

 

I didn't. Jaguar service replaced them when they fixed the cracked t-stat housing problem. Yes, they apparently were fine for at least 7.5 years after I reused them. I'm relaying what Jaguar told me. The original Jag constant tension clamps do look nicer than the shiny worm style. I recall thinking when I 1st removed them that I didn't like the design since you couldn't add more tension just let go & however much spring was left in it clamps down at a fixed pressure. With old stye worm ones you can turn that screw & crank down.

What you say makes sense if the constant tension ones do maintain their tension after many years & then you release the tension & expect them to reapply same tension. Mine did for 7.5 years. I don't know that when a hose gets soft the worm style now is not tight enough. I defer to your experience on that. I assume if that happens you need to replace the hose anyway. Interesting.

 

I understand how to handle the large clamps and will reuse them due to their spring action as discussed. BUT, how do you get the small clamps off on the small coolant lines? And can they be reused or should they be replaced with worm clamps?

EZDriver

 

To remove the little locking clamps you squeeze the humps slightly to remove the tension with a pair of pliers and then use a small (tiny) screwdriver to lift up the outer part of the clamp. Pops apart.

Mine have been reused several times.

 

thanks Test Point. That is just the info I needed.

EZDriver

 

Replaced the thermostat housing with a Welsh aluminum unit. Didn't have to. Thermostat went bad so I figured I might as well do the whole job. Having a 8mm "crows foot socket and 12" extention makes the job go a whole lot easier. In a different thread I mention the local mechanic, I use the term loosely, didn't have the crows foot socket and we had to loosen the intake manifold to get at two bolts with a regular socket. Jack

 

Excellent guide Gus!

Just did my Mom's 98 vdp. The 8mm crow foot made it possible for me, since tools are limited here in Ca. All my stuff is in Chicago.

I used a long nose offset plyers to turn those 2 back screws.

The back drivers side touches the intake manifold when removing it, which IMO is bad design. That screw could be 1/4 inch shorter and still function fine.

Generally went well, except when I leaned on the 1/2 water line and broke it($21.00). Also had some leaking at the passenger side water inlet sooooooooo took it off and cleaned around the area a bit.

The metal clips on the old plastic housing was a pain to get senors unplugged, soooooooo broke the bracket off the plastic I wasn't using anymore anyway.

 

EZDriver,

The plastic is "bakelite" which is one of the first forms of phenolic plastics ever invented. It was designed for use in household electrical appliances because of its insulating qualities, and even there it becomes brittle.

The slow leak problem is caused by the Bakelite fitting gradually warping, and yes, it is difficult to spot because the coolant gets evaporated away before it can get to your garage floor. Carrying out ‘patch’ repairs is (a) a waste of time, since the problem will return (b) risky, because catastrophic failure can & does occur, and if you don’t observe it in time you can destroy your engine. (See Iconoclast’s thread) Such as being very busy with driving in trying circumstances when it fails. The aluminium housings are much better, and should last as long as your engine. They also come as a kit, which means that you get to replace everything at the same time. The thermostat is the only ‘extra’. I strongly suggest you don’t allow a Jaguar Dealer Service Advisor to talk you into fitting the ‘genuine’ replacement, which is, after all just another Bakelite unit with failure built in at manufacture.

As for timing chains, they are not the quality that the old in-line 6 used. The current crop are a single link chain manufactured down to a price, not up to a standard as the old Reynolds double link chain was. It is penny wise & pounds foolish to change the top chains without changing the bottom chain at the same time. A breakage of either will do just the same amount of damage, and rebuilding engines is expensive. I would also suggest that it is worthwhile finding an industrial engineering supply company and getting top quality chain rather than fitting a Jaguar Genuine ‘Cheapy’, which will probably cost as much if not more.

The same with the tensioners. The original in-line 6 tale repeated. The tensioners have been covered elsewhere, but my understanding is that there are Ford Lincoln tensioners available with fit the bill. Again, don’t be tempted to refit a used tensioner – the savings ‘ain’t worth the candle’.

And Gus’s site at www.jagrepair.com does indeed look like a damned good site. Congrats, Gus.

Cheers,

Languid

 

p.s. If you are capable of DIY, buy yourself the bent (crow's foot) spanner from a toolshop (I saw mention somewhere that it is 8mm) , as it will still be cheaper than paying a Franchise Dealer, and you will then have the tool for any future work for which it may be useful. Over the years I have amassed a braod collection of all sorts of tools for all kinds of jobs, and still saved a poultice -v- paying a Dealer.

Languid

 

Gang;

Great posts and info.

My question is does this plastic/Bakelite thermostat and housing apply only to 4.0 engines or to the 4.2 series as well?

And should I be concerned and looking for this on my '04 XKR?

FYI Many early cars had Bakelite steering wheels and components.

cheers,

jj