I JUST took it out and it measured 49.3776 mm. Ill heat it up and see what it does.

and......it didn't do anything at all.

I mean...i could be doing something wrong but sitting in a pot of boiling water for 10 minutes should get it open lol.
I pushed on it with my fingers and eventually it opened. Obviously need a new one, tested it again and unsticking it and it still didnt open

 

okay i have to say FINALLY something easy to do on an XJS thank you jaguar for not putting a thermostat on the water pump.


im still gonna check the RH but im going to assume the thermostat failing is what caused this overheat and the the heater hose to blow out since it is on the LH side and probably got alot of pressure.it says MADE IN ENGLAND which could just be an OEM part but at 83k miles i wouldnt be surprised if it were original. And if the Jaguar ones don't open all the way like you said it would make the thermostat wear out faster too.

 

OK, that sounds toooooo long for a closed stat, it should be about 35mm, and they open 8mm (ALL of them), and that equals 43mm +/- 1mm for tolerences.

I have a paper, with photos, from my days of cooling system training with Tridon here in OZ. It expalins how stats work, how to test them etc etc. I tried to upload it as an attachment, and it is 6mb, and the system said "upload failed", so sorry I have no more ideas.

Let me know your email address and I will PM it to you or anyone else for that matter, who may be intersted.

 

my email is mcdowell92@gmail.com

am i measuring something wrong? because that is alot larger than what you are saying and i just assumed you meant the whole thing.

 

OK, got that.

I will sort and email the attachments tonight.

Also, please keep this thread active of your findings, as I believe firmly in keeping the wider community informed of findings, either good or bad, and the search archives only grow from thread postings.

 

yeah i agree i like putting stuff out there.

okay SO.
I haven't checked to fit but i was about to measure the length of the new thermostat just to post it...its pretty different.

the new one is 59mm long.
The diamter is like 53.9mm on the old one and this one is 46.9!!!

what gives?? this is a duralast brand part bought at AutoZone listed to fit an 88 Jaguar XJS v12.

I still wanna go put it in and see what it feels like but its completely different from the old one.

the new one has alot more copper on it but the spring tension is also way higher. Cldnt hurt to test it right?

 

I've been following this thread and I'm sure glad to hear that it's not the head gasket

I had to do the thermostats on my v12 recently. I don't know too much about all the sizes but the ones I got from napa looked different mainly the absence of the jiggle pin thing.

I searched the old threads and I found that you can drill 1/8 hole in the same place and it will work fine. Just make sure when you install it is at 12:00 as I believe it is where air and steam escape. I did this and haven't had any problems mine is a 6.0 but I don't think it makes a difference

Good luck with the repairs

 

hey thanks alot man I really wouldn't have worried about it unless someone had mentioned it.

I didn't know wtf it was for but i haven't seen one before and figured it was an over-engineered trinket kinda thing which i didn't need to worry about.

I suppose its not big enough to matter but big enough to make a different with overpressure or whatever it is.

 

AHA, now that is what I had with mine, the stats are TOO SHORT (old ones I mean), and that will NEVER close those by-pass ports.

The new one will by the look of that one.

The measuring of length etc is done by measuring from the "larger" flange, to the smaller flange/disc at the bottom. Basically the distance between the 2 flanges/discs.

The "top hat" section "above" that large flange is of little importance in our application.

 

aahh that makes sense.

in that case the old one measures about 35mm long and the new one is 47mm.
So i guess thats GOOD, what about the diameter being different. im probably gonna go stick it in before someone else responds but im rly wondering.


ALSO you can't see it in that pic but the new thermostat DOES have a hole in it with a pin but its on the inside not the outside edge.

 

so grant what are bypass ports doing? you mean it being short means there is never 100% flow to the radiator and some of it always goes back to the engine?? Probably MORE since it would be less restrictive.


in other words everyone with a 5.3 go spend 20 bucks and 30 minutes and change your thermostats now.

These are also 180s, idk how prominent the 190s are but im glad.

 

okay so some more stuff on the thermostats

the jaguar one is DEFINITELY too short and doesn't do anything, I would guess because of the reduced pressure compared to the open end probably 60% or more of coolant goes right back into the engine. IF this is seriously what every jaguar V12 had in it then THIS is why they are known for running hot.

I have it set to the Depth of the thermostat housing and here is the Jag thermostat next to it.


Here is the aftermarket one, it is the perfect length


now for the diameter issue.
Once again the aftermarket one is BETTER.
I forgot what the measurement was but the OE is TOO BIG. Sorry for taking pics before cleaning the gasket off.


anyways that lip isn't from the gasket, its actually cut into the housing. The OE thermostat will not Seat into it because its too big, the aftermarket one DOES and has maybe 1mm of space.




you can see some of the gap at the top where there is room for the thermostat to actually fit back into the housing and seal


again sorry for the nasty pics with the gasket still on there and idk if you can actually tell how they fit differently. in the new pic you can see on the top where there is a bit of a gap.

The RH side is just as deep and just as wide. I recomend ANY jaguar XJS owners replace there thermostats asap, this is such an easy job and the probably whole reason they run hot.

 

I took out my relay for the aux fan. I can't find my test meter so idk what to do. I hooked up 12v to it and there was a single combination where I cld hear the relay clicking, so i think it works unless there is something else.

Im trying to figure out how to test the temp sensor with nothing right now

 

OK, those stats look fine to me.

The ones you took out, for some reason are just plain wrong.

The diameter of the large disc should be 54mm.

The distance from the mount flange to the lower disc on the stat should be approx 34-35mm.

Taking ALL into consideration, I reckon that the temps got wwaaay too hot due to coolant loss, and NO sensor will operate if it is not in contact with liquid. It will not/cannot sense steam, so it will NOT switch fans on. I might be wrong, coz I seem to remember you had the temp gauge reading MAX, so coolant must have been in contact with its sensor, and it is way above the fan switch???.

That fan switch in the lower hose inlet spout can be a mongrel to get out with the radiator etc in the way. It is a 24mm (memory) spanner size, and heating it in a pot of water, with a meter attached (set on ohms), and a thermostat dangling to see when it actually goes off is the only way. It will have its temp stamped into one of the flat sides. Mine is 85c, and some I have seen are 82c.

I would make sure that the small "over temp" fan actaully does work, as they are well known to NOT, due to siezure.

 

lol my dad is out of town and took the test meter with him so idk how i can test it now.

the fans and shroud are out because the aux fan wasn't working. it is REALLY easy to remove with them out of the way.

My fan DOES work, i hooked it into my battery. So all thats left i guess is the relay and temp sensor?? I hooked up my battery to the relay and got it to click on one combination, idk if there should be more. So im guessing its the temp sensor i just have no way of checking atm.

found out my slow coolant leak has been the large hose at the water pump, its just loose at the top. i guess it didn't blow since most of the water pressure was in around the engine with the stats being the way they are.

 

okay so correct me if im wrong...but the temp sensor. If i heated it up to the right temp and then put a positive connection on one side, it SHOULD spark when i touch the negative side if its heated up to the right temp and is working properly.


right?

 

NO.

Forget about volts etc when testing, too bloody hard and dangerous.

Set the meter to Ohms, around 2K ohms will be fine, join the 2 probes of the meter cabling together, and the digits should read ZERO, or VERY close, and that constitutes a continous circuit, whereas a "1" on a digital meter indicates an open (broken) circuit.

I will NOT discuss resistance, as it is NOT required for this basic ON/OFF exercise.

Connect the 2 probes to the switch therminals, set the dial to Ohms, and observe a "1" on the read out, now heat up that switch in a bowl of water,and watch the thermostat rise, and when it gets to, or VERY close to, the switch stamped temp (82c, 85c whatever) observe the meter reading Zero, or close to that.

Test is over, either the switch works or it dont, NO sparks, No funny happenings due to lectrikery being in the area.

 

[quote=sidescrollin;401465]aahh that makes sense.

in that case the old one measures about 35mm long and the new one is 47mm.


You got me worried a bit here, and I am a tad late replying, another night in the Hospital, chest pains AGAIN, damn I must drink more, pain ceases when alcohol is present, found NOTHING again, so I am back to annoy for a while longeer, haha.

The thermostat length you require MUST be 35mm, CLOSED, or VERY,VERY close to that. You must also measure the OPEN length, that is when in boiling water on teh stove, and you are looking for 43mm, or maybe 44mm, NO MORE.

If those aftermarket stats are 47mm CLOSED, and you are measuring them correctly, they will open to 55mm and will JAM, and the engine WILL OVERHEAT AGAIN.

Please make sure that the stats you have as replacements are either a DIRECT Dayco DT18A, or a PROPER crossreference for that number.

The DT18A is 35mm CLOSED, and 43/44mm OPEN, and the spring loaded disc at the bottm has about a 6mm travel length, and that is FINE.

The DT18A is 54mm diameter, as is the proper Jag stat, so dont get caught with 52mm stats, they will NOT seal.

I CANNOT STRESS ENOUGH, THAT IF YOU GET THESE STATS WRONG THAT ENGINE WILL BE TOAST.

Measure those "new" stats again, and if they are 47mm from disc to disc, DO NOT fit them.

I am going for a snooze, feel tired with the "drugs", I will come back later and make sure you have a good grasp of all this thermostat stuff. It is SO SIMPLE, but concentration is paramount, and I just cannot concentrate well enough at the moment.

 

[quote=sidescrollin;401469]so grant what are bypass ports doing? you mean it being short means there is never 100% flow to the radiator and some of it always goes back to the engine?? Probably MORE since it would be less restrictive.

OK, I am back, snooze is over.

The by-pass ports "very basically" allows the coolant to recirculate inside the block, which aids in "fast warm-up", and that aids pollution equipment efficiency, etc etc.

So on the V12 with 2 stats, the ports are linked with the steel pipe across the front of the engine, which also has a hose to the top of the water pump, suction side, as with the lower radiator hose.

So the coolant goes out via the by-pass ports (the engine is COLD), and is sucked back through the top of the water pump, and forced back into the engine. NO (almost) coolant goes through the radiator at this temperature. This process heats that coolant quite quickly, so each time a given portion passes the stats, it is HOTTER, and eventually the stats start to open (crack temperature), so SOME coolant goes via the radoator, and is cooled, and this process continues until the designed operating temp of the engine is reached (about 90c), and by this time the stats SHOULD have those ports FULLY closed, so ALL the coolant goes via the radiator. BUT, the stats MUST NOT be fully open, coz if they are they have LOST CONTROL of the cooling system. There is ALWAYS a working margin.

In the case of the engine cooling too much, such as coasting downhill for some time, the stats will start to close, and may re-open the by-pass ports slightly, which decreases radiator flow, and re-instates recirculation flow, and when the power is returned (power equals heat), the coolant temp rises to 90c again, and the ports are closed once more.

Just to further add a statistic. You already have this in those PM's I sent you. The thermostats (ALL of them) open 25% of the diameter of the throat bore of that stat.

The stat opens at a "crack temp", in this case 82c, and is FULLY open at 12c above that, so 94c in this case, and since the engine opeates at 90c there is a 4c margin here also.

So a stat with a 32mm throat, will open 8mm, SIMPLE. So the 35mm closed length stat I use will open to 43mm (it has a 32mm throat), and since the by-port is 41mm below the mounting face, there is a 2mm margin, so that by-pass port is well and truly CLOSED before the stat gets to 90c operating temp. Remember a stat working at MAX temp (94c here), and/or MAX opening length (43mm here) is USELESS, as it has lost control of the engine cooling system.

Since the by-pass disc is spring loaded, it allows the piston section to travel down inside the by-pass port, thus allowing the stat to continue to open and close slightly to control the required engine temperature WITHOUT re-opening that by-pass port. Very simple when you sit quietly and look at the principles of the cooling system of ANY car.

 

yeah i didn't know you meant to the rim before, they are 41mm closed.

i agree with you, and honestly I didn't ever pay enough attention to how they work before i took these out, but its SOOO simple. Sometimes it astounds me how simple things work on cars. Like its technology from decades ago but its theres nothing wrong with it so don't change it.