Please help me work this through !

I developed a slight leak from the cap of the thermostat housing on my year 2000 XJ8 4 litre.

I have tried tightening. I have tried a new cap. I am trying varying amounts of torque on the cap. Less trque gives less leak ! I am trying PTFE tape / two rubber seals instead of one. I still get the same slight leak. The housing looks fine.

I left the car running for 15 minutes to test the cap and now notice water from the exhausts. I have never noticed similar water from the exhausts before. (I'll post up a photo.)

I am now getting paranoid that I may have a head gasket problem leading to pressure in the coolant system and coolant causing moisture in the exhaust gases. THIS CLEARS totally after driving two mles.

As you can tell... I am not a seasoned expert !

Is this head gasket failure ????

Is this just a simple thermostat cap problem. If so is there any simple fix short of fitting the aftermarket thermostat housing ? (Thanks for previous advice on this in last post !)

Will I harm an XJ8 by trying some RadWeld in the coolant ?

 

send me a ireland license plate and ill tell you

 

take that spring clamp off the hose on the side of the t stat housing and replace with a worm clamp you can tighten. I think youre just chasing a leak at that hose now which is common and misconstrued as the cap continuing to leak. Moisture from the exhaust is normal condensation. I wouldnt worry unless you get white smoke out too, and then if the car begins to runs rough and use coolant. many time too you get pressure from the reservoir if you put your hand over the top to try a momentarily seal. you can also use a block check kit that checks for exhaust(hydrocarbons in the coolant) but again I seriously doubt based on this and your other thread this is the issue....and Im serious on the plate too Ide love to get an Ireland plate

 

Thanks Brutal,

I'll see what I can do on an irish plate. (I'm over in the Orlando, US next month so if I can find one off an old family car then I can put it in internal mail !)

I am 99% certain the leak is from the cap thread not the pipe. This is because I have been carefully observing fluid forming from the thread, not the pipe multiple times and drying up fluid with paper towel and watching it recur from the front edge of the thread (where the plastic housing design has some of the thread missing.... designed that way !). Also I made it go away by over-tightening the original cap (and then fracturing the inner plastic of the cap leading to the need to replace the cap !). I have looked carefully at the thread and convinced myself that there is no fracture.

There is pressure at the reservoir when it is sealed by the cap for ten minutes running the car from cold. However: Starting the car with the reservoir cap off and running... there is no obvious pressure under the palm of my hand after a two or three minutes.

I am tightening the cap only by hand. I have tried two rubber seals plus PTFE tape. This gives the best seal... but still slight leak. On my 1976 Triumph Stag, an old boy who knew Triumph engines well just said to stick in Radweld to the coolant rather than tackle a similar leak (on the water pump in that car). I'm getting tempted to try the Radweld (coolant sealant).

My torque wrench doesn't go below 40 and I have estimated that 9Nm is less than I can achieve with my hands. I find the leak is LESS the less I tighten.

I may end up taking a sledge hammer to the car if it continues to beat me !) But seriously... what next >?

Thanks,

Graham

 

give the new clamp a try, just to rule that out, coolant could be just collecting there to give u the impression its the cap, from what brutal has seen, its possible.

 

I tighten till the hex tool almost skips to get to tighten. As i have had issues as well, many times though taking out the seal in the cap and flipping over seems to work, as does using a medium set of channels locks on the outside of the cap instead of the hex fitting in the cap, gentll grabbing enough to bite and tighten.

 

Nearly there !!! Thanks for this.

Following these techniques I can get to a position where there is only the slightest leak. (Maybe one drop forming per minute... but it mostly evaporates due to heat !)

But then if I tighten 5 degrees further, the leak gets much worse.

Is this avery unusual story... or is this what I should expect from the plastic thermostat housing ? (and a standard reason for abandoning the plastic housing ?)

I know the RADWELD or BARRSLEAK would seal the leak if this were my 1970s car.... but I don't want to screw up a more complex engine. Would I be mad to chuck some into the coolant of an XJ8 engine??? I'll post link below incase the product has some other name in US.

http://www.halfords.com/webapp/wcs/s...egoryId_165750

http://www.barsproducts.com/PLT11.htm

I think I know what your'e going to say about this stuff... but I could be wrong !

Or shouldI bravely continue to tighten further and risk damage to the housing plastic thread ?

Thanks again,

Graham

 

Why not buy the aluminium thermostat housing replacement on the internet, and then fit it ?
It sounds like there is a crack in the plastic of your present housing somewhere. Cracking of the plastic thermostat housing is also a favorite of the Rover 75 V6 engine, and an enterprsing chap in South Africa makes and sell aluminium replacements.

 

I recommend the aluminum cap and housing as well. I struggled with getting a new cap to seal. If I had to do it over I would get the aluminum housing and be done with it. But for your situation, this is what I did to get my "new" cap to seal. I pulled the inner rubber gasket out and made a new gasket using the same high temp rubber gasket material. I made it a bit oversized so that it fit tightly inside the cap. I noticed on the oem cap that the inner gasket does not fit the entire inner cap surface. The oversized gasket does not get squeezed or pinched when tightening and that is what I feel has sealed my cap.

If it leaks again I am going to the aluminum housing.

Also, I don't know about anyone else here, but I would never use the stop leak stuff in any situation. If it seals the pin hole leak you have at the cap, you can count on it sealing a bunch of other things inside the radiator.

 

Thanks everyone,


As per your descriptions above.... I have indeed spent a lot of time messing around with the cap. The problem seems to be exactly as you describe. I kept trying because I was convinced there is no crack and that it must be possible to get a seal. I also wanted to avoid the time on those two rear 8mm bolts that the job involves. But the facts are exactly as NorCalDiesel describes i.e. No crack but the seal just doesn't quite seal !!!!

I have found the aluminium kit that people seem to order in te US ( http://www.motorcarsltd.com/AJ82217.KIT.html )

But I am in Ireland and ordering from the UK would be easier. Could anyone confirm that the link below to a UK vendor is actually listing the same kit or a "good enough " kit?
http://www.britishparts.co.uk/.sc/ms...0KIT-ALUMINIUM

Thanks for you patience !

Graham

 

The price difference seems too great to be the same manufacturer. I suspect the Jagparts one is made in the Far East, the USA one is made by Welsh Enterprises and is therefore probably a domestic product, hence the price. ($66). However if you convert $65 to £ you get around £45 about £10 more than the Britishparts one. The picture on the Welsh Enterprises website shows a very nicely made article

I would go for the Britishparts one. They are a reputable supplier. You could of course, e-mail them to ask if it is the one from Welsh Enterprises