Thermostat Change V8V
Discussion
Just changed the stat as running cold on run but ok ish around town.Bought correct AM part & o ring but subsequently found that Jag part AJ811788 is identical & about 1/3rd the price! O ring is AM part.A bit fiddley as no longer have young flexible fingers but worth doing as only takes about 1 hr or so. Typical failure with the sealing ring on the stat (not the o ring) having split away & jammed the stat open---see pic 
Gettoff said:
Jockman said:
mine was replaced under warranty 2 years ago.
Seems to be a common issue
Evening Jockman, is this normally a straightforward warranty claim? as I think mine has this fault.Seems to be a common issue
Will put this into the FAQ's. DMS used to have a picture, but with their demise the website went as well.
, promise not to ask any insurance related questions.. 
Here is how I replaced the thermostat when I had a V8 - I used the Jag part which is substantially cheaper than the AM part and is identical.
The thermostat I used is for XJ naturally aspirated from (V) H17519 / XK naturally aspirated from (V) B23158 part number AJ811788 - I was lucky and found a new one on Ebay for £10
You may find a better/quicker way - the first thing you need is the patience of a saint and the hands of a gynecologist
and buy a magnet on a stick!
As I could not find a drain point on the coolant system I put a large shallow (1" deep) catch tray under the car - you may want to remove the undertray (I didn't)
As you look at the engine undo the electrical connector under and to the left of the throttle body.
undo the two the two (8mm spanner size) bolts that hold the black plastic cylindrical oil separator from the alloy bracket pull upwards about an 1" or so to release and twist on the pipes until out of the way.
Remove the two (8mm spanner size) nuts holding the bracket onto the thermostat housing - this is where you need the aforementioned dexterous hands or a magnet on a stick - you will drop them - I did!
Remove the (10mm spanner size) bolt at the font of the engine holding the bracket to the engine.
Now for the tricky bit - on my car the stud (nearest the head) was about a 1/16" too long to allow removal of the bracket (it would not clear the head) - I overcame this by using a die-grinder and a small ball-tip - I had to grind about half way down the plain shaft try not to go as far as the thread (I have heard that not everyone has had this problem) - pull the bracket clear.
Once you have overcome that, remove the two studs (13mm spanner size) and then the (8mm spanner size) bolt (this is a bit of a b*st*r*d) - pull thermostat housing off and hope you put the catch tray in the right place - about 1 to 2 liters of anti-freeze will come out.
Swing the housing/pipe clear so you can easily (relatively) access the thermostat
You then remove the thermostat by pressing down with your Arnie Shwarzenegger fingers, twisting at the same time - it's fairly obvious and not that bad really, resist the use of screwdrivers etc. the pin may be stuck into the housing at the pipe end pull it out and don't drop it down the pipe.
Make sure the rubber seal in the housing is ok, this is not a Jag part and there is no problem re-using the original provided it's intact and not twisted.
Re-assembly is just the reverse of the above procedure but getting the nut back onto the stud holding the bracket (the one you may have to grind) was a real bind - jam a rag underneath so if you drop it, it doesn't trap itself in an awkward or dangerous place. Use a dab of thread-lok on any bolts/nuts.
I reused the anti-freeze I caught, if you have to top up make sure you have the correct stuff - O.A.T. spec. Check for leaks, start her up - again check for leaks.
If you have all the tools to hand and armed with this info you should do it in about an hour and for less than £50.
Disclaimer - I am not an AM mechanic - this is for reference only - if you lose your fingers, sanity etc - don't blame me.
I have also put this info on the Wiki as it does seem to come up regularly - the V12 thermostat is I believe a different design and none of the aforementioned will be relevant for any V12 AM engine.
The thermostat I used is for XJ naturally aspirated from (V) H17519 / XK naturally aspirated from (V) B23158 part number AJ811788 - I was lucky and found a new one on Ebay for £10
You may find a better/quicker way - the first thing you need is the patience of a saint and the hands of a gynecologist
and buy a magnet on a stick!As I could not find a drain point on the coolant system I put a large shallow (1" deep) catch tray under the car - you may want to remove the undertray (I didn't)
As you look at the engine undo the electrical connector under and to the left of the throttle body.
undo the two the two (8mm spanner size) bolts that hold the black plastic cylindrical oil separator from the alloy bracket pull upwards about an 1" or so to release and twist on the pipes until out of the way.
Remove the two (8mm spanner size) nuts holding the bracket onto the thermostat housing - this is where you need the aforementioned dexterous hands or a magnet on a stick - you will drop them - I did!
Remove the (10mm spanner size) bolt at the font of the engine holding the bracket to the engine.
Now for the tricky bit - on my car the stud (nearest the head) was about a 1/16" too long to allow removal of the bracket (it would not clear the head) - I overcame this by using a die-grinder and a small ball-tip - I had to grind about half way down the plain shaft try not to go as far as the thread (I have heard that not everyone has had this problem) - pull the bracket clear.
Once you have overcome that, remove the two studs (13mm spanner size) and then the (8mm spanner size) bolt (this is a bit of a b*st*r*d) - pull thermostat housing off and hope you put the catch tray in the right place - about 1 to 2 liters of anti-freeze will come out.
Swing the housing/pipe clear so you can easily (relatively) access the thermostat
You then remove the thermostat by pressing down with your Arnie Shwarzenegger fingers, twisting at the same time - it's fairly obvious and not that bad really, resist the use of screwdrivers etc. the pin may be stuck into the housing at the pipe end pull it out and don't drop it down the pipe.
Make sure the rubber seal in the housing is ok, this is not a Jag part and there is no problem re-using the original provided it's intact and not twisted.
Re-assembly is just the reverse of the above procedure but getting the nut back onto the stud holding the bracket (the one you may have to grind) was a real bind - jam a rag underneath so if you drop it, it doesn't trap itself in an awkward or dangerous place. Use a dab of thread-lok on any bolts/nuts.
I reused the anti-freeze I caught, if you have to top up make sure you have the correct stuff - O.A.T. spec. Check for leaks, start her up - again check for leaks.
If you have all the tools to hand and armed with this info you should do it in about an hour and for less than £50.
Disclaimer - I am not an AM mechanic - this is for reference only - if you lose your fingers, sanity etc - don't blame me.
I have also put this info on the Wiki as it does seem to come up regularly - the V12 thermostat is I believe a different design and none of the aforementioned will be relevant for any V12 AM engine.
Edited by laracer on Thursday 28th February 19:36
Edited by laracer on Thursday 28th February 19:36
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