Hello There,
The Thermostat housing and manifold or outlet pipe is leaking on my 2003 S Type with the NA 4.2 motor and has to be replaced. I am hoping to leave the engine coolant inlet pipe that comes out from under the throttle body and intake manifold and just replace the outer part that is leaking. Has anyone done this? Is it hard to remove the outer part without damaging the inlet pipe? Does it just slip off or need to be heated or anything? Do you apply coolant or anything to the parts and O-rings, or just put it together dry? Any input would help. I'll try to attach some pictures of what I'm talking about. I think the reason for this and heater valve failures, etc. is when the reservoir cap doesn't relieve the pressure any more and the excess pressure breaks everything. But that's a matter for another post, I guess.

 

It'll just come off just be gentle, no heating nothing special

 

I rebuilt the cooling system on my 2004 S-type a couple of years ago and I just replaced the whole assembly. I think the issue is deterioration of the plastic due to temperature and age. There a number of reports of cracking in various pieces.


It makes a lot of sense to replace the whole thing. During assembly I used only silicone grease on the rubber O rings. No "artificial sealants!

 

Agreed - replace the entire plastic assembly. I had to do this last November on my wife's 2006 XK8 when the thermostat housing sprung a leak. As mentioned above, the plastic components tend to get brittle and warp as time passes and heat cycles add up. Your safest bet is to replace the entire coolant outlet duct, and it is not that much more costly to do so rather than just the thermostat housing. If I remember correctly, it was about $40 more to spring for the entire XK8 assembly vs. just the thermostat housing....

Replace it all and be done with it. You'll be glad you did....

 

I'm not worried about cost of the part, the inlet piece comes with it, I'm planning on replacing the whole outlet piece pictured on the left, I just wanted to leave the large inlet piece that goes under the intake manifold, so I don't have to take the throttle body and intake manifold off to get to it. The motor works great, I don't want to mess with it if it isn't necessary. Didn't you have to remove the throttle body and intake manifold to replace the whole plastic assembly? I think a lot of the plastic components fail from too much pressure in the coolant system when the reservoir cap doesn't function right, not releasing the excess pressure. After finally getting a new cap I can feel the difference in the pressure when I squeeze the main hose on top. It used to be hard as a rock when the car was up to temperature, I thought that was normal, it isn't.

 

I did remove the throttle body, but not the intake manifold. You can get the whole thing off and on if you work carefully---removing the rear studs and reinstalling them requires some dexterity.

 

I don't know about the non super charged v8 but I had the option
To upgrade to a full alloy unit to replace the plastic junk on my str!
It was only $100 more than the plastic so I went for it and mine wasn't eaven
Leaking , I just have no faith in the plastic component after reading about so many
Fails!!
Might be worth a look into .

 

The water outlet pipe on the 4.2 litre NA is a different design from the SC outlet, so the parts are not interchangeable.

 

You can certainly just replace the outer part of the water outlet that contains the thermostat, but eventually you must replace the entire assembly as the vehicle gets older.

A small amount of silicon on the sealing ring should help make assembly simple. Be sure to check the condition of the sealing ring and replace it with the one from the new part should there be any signs of leakage.

It is also a good idea to put anti-seize compound on the threads of the four bolts that hold the assembly to the respective cylinder heads. Check the condition of the five hoses that connect to the assembly for any seepage. Use the constant-tension hose clamps that came originally on the vehicle as they exert less pressure on the plastic parts than the type that tighten by means of a screw head.

 

Yes I saw that the parts were differant
but I thort maybe the NA engine mite have an
Alloy option as well ?

 

While there are aluminium versions available for the NA 4.0 litre AJ-V8, there are none for the 4.2 unit, which is a very different design.