Hello everyone. I consider myself a pretty experienced DIY'er although new to Jaguars, but I'm a little confused as to why I ran into my newest problem. Is the thermostat housing known for weakness issues? Also should I stick with the flat gasket, use the O-ring, or both? I went to start my xj6 yesterday morning, and thought it would be good to toss the new thermostat in real quick.. Well the old one was installed with the flat gasket only, and the new one came with the O ring, so I tried to install it with the O ring and there was a gap. I thought it just needed to be tightened down to seat properly, and ran in the top bolt half way, then started on the bottom one. It was starting to get a little tight but not what I would think was over-torqued at all, and much to my surprise and dismay I hear a sharp "click" sound. Sure enough I take the bolts out and the only thing holding the lower tab on was the fact it was stuck to the old gasket, which I had left as it was intact and I thought it only to be secondary with the O ring being installed.. Did I apply too much pressure on the tab? Should I not use the supplied O ring? Would it have had to have already been developing a crack to break so easily? It was about 40 degrees Fahrenheit, does this level of coolness make it brittle? It just seems like an issue I shouldn't have had but I'm also used to thermostat housings either being plastic or steel, not aluminum.

I have already located and ordered a replacement, which will be here Tuesday according to the tracking number. I just want to make sure I don't do something wrong and manage to break it again, as such a small and simple piece did run me a total of $35 + shipping for a used salvage part. It looks like I can install my new alternator this weekend, but starting the car and testing it out is out of the picture until later.

 

This housing is basically made of a carrot cake material and it will crack easily as soon as you start forcing that damn o-ring there. I did exactly the same thing myself many years ago, then couple years later I went for 4000 miles trip and thermostat failed on my way and since I didn't have much time and couldn't be bothered with the top shock bushes that also needed replacement I took it to a local garage and by the time I reminded myself how weak it is and got up from my seat walking onto the garage floor, it was too late and the guy was walking with the same cover cracked in half.
Simple thing to do is to not use that o-ring there at all, its not needed. If you really want to, then file the edges so the o-ring fits in perfectly flat. Remember, any gap and any force and your replacement will also crack. If you have access to a tig welder, they can be repaired easily. Re your alternator, no problem trying the car with no coolant in the system, obviously just don't run it for 10 minutes+ and you'll be fine.

 

Yep.

Nearly ALL parts suppliers list a gasket, AND, an o/ring.

If YOUR car has the gasket, that's all it has.

If YOUR car has the o/ring, that all it has.

NEVER both.

The other reason is the stat is mounted vertical, and gravity is a fickle sucker. I always clean the seating ridge, a SMALL dab of RTV at 12o'clock, and fit the stat. Hold it there whilst you consume a beer with the free hand, then it will stay put, and not slip down and cause that housing to crack, and basically ruin your day.

Always fun.

 

Oh okay, well lesson learned then I guess! "Oops!" I will be careful and leave out the O-ring this time. As far as running the engine, if it just had water in it I would, but I just flushed the cooling system and put fresh coolant in it last weekend, So I'm trying to avoid running it all out on the ground. Thanks for the quick replies guys, I feel less bad now that I know it's an easy part to break if not installed correctly.

Would it be alright to use permatex ultra-grey by itself or do I need the gasket? One I have on-hand, the other will have to be ordered.

Also, do you think JB weld will be strong enough to repair the broken housing? I plan on waiting for the replacement, but it would be nice to have a spare. TIG would be nice but I neither possess the skill or equipment.

 

JB Weld has kept most of my Jags moving in a forward direction for longer than I can remember. NOT the fast dry junk, the Original 2 tube formula for me.

RTV is fine if applied as specified, and that also has saved my rear end (human one) on many occasions.

 

Thanks again for the advice, I've never seen anyone have much luck with the "kwik weld" version or whatever it's called, but I'll pick up the good stuff and save this one for a backup!
I went ahead and ordered an OEM flat gasket from eBay for about $6. If the housing shows up first and I'm too impatient then it can go on the spare parts shelf with the extra thermostats I ordered and wait for a future service.

 

The 'O'ring is for the AJ6 engine ONLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

bob

 

If you need a thermostat housing casting let me know as there is one on a toasted engine on a X300

 

Thank you, I wish I had thought to ask here first but I was in a rush so I had one ordered within a few hours of the mishap.

 

Ta da!!! Now back to other problems...lol..

 

Well done.

Simple fixes on simple cars.