Where's Da Thermostat?

Finally figured out why my heater hasn’t been blowing very warm this winter, or the needle on the temp gauge moving as fast or up to where it should be: my thermo is apparently either missing or stuck open. :thinking:

I have bought a replacement and the seal, but where is the thermo at??? The factory workshop literature makes it look like the thing should just be looking me right in the face when I open the hood/bonnet, but it sure isn’t. The name itself seemed to trigger something in the back of my mind. :pensive: Figuring that it must be in the general vicinity of the radiator and or the upper rad. hose, I have looked carefully but can’t spot the thermo. housting. It must be hidden behind or under something, in general Jaguar style :angry: What do I need to remove to find and r/r it? :confused:

btw, after buying my first choice (“Duralast”) for the replacement unit, I took it back to the store and switched it out for a few $$s more for the “Fail Safe” brand, after doing a bit of online research. That brand name itself seemed to trigger something in the back of my mind.
:pensive: When I originally asked the auto store clerk whether it would be worth a few more $ to opt for the FS brand, he said “not really”. However, I then learned that F.S. is apparently the only manufacturer (they have the patent on ti?) of thermos that are designed to always fail in the OPEN position, rather than closed. No overheating worries with that one then. In fact, I wish Harlem, my 2000 XJ8 had a F.S. in it, as it failed last year, stuck in the closed position, almost stranding me on a side street when the temp suddenly went through the roof. :rage::

What year is your XJ-S/XJS and what engine does it have in it?

Paul

It’s Superblue, my '94 4.0 …

Dang, I just discovered something else, though. The factory workshop literature shows the rubber sealing ring (“O”) as going between the thermostat unit and the thermo. housing, whereas the Jaguar Classic parts site drawing shows it going on the OPPOSITE side of the thermostat, between the thermo and the thermostat cover. :crazy_face: So which is it? Without having yet (found) and removed the thermo. cover, my gut feeling is that the Classic location is the correct one, for the simple reason that that is the side of the thermos that has a recess around the perimeter which matches up to the O ring. :thinking:

O.K., finally located it. :persevere: That’s the good news - the bad news is to access the pair of bolts on the thermos. cover the cold air intake horn has to be removed from its front opening at the top of the radiator assembly to swing it out of the way. The problem there is that the end of the horn flares out, like a trumpet, on the other side (front) of the front opening. I don’t see any way to be able to push the horn out or pull it in from the opening. :pensive: IIRC, I had this same problem once with either one of my XJ40s or possibly my X-300 when (I had her. I think the “lip”/flare is supposed to be a seperate piece, and it somehow detaches from the main part of the horn. However, i have tuggede and tugged on it and it won’t come loose, even with PB Blaster applied. (hopefully some idiot PO that removed her didn’t superglue the two pieces back together :angry:). If I can’t find a way to seperate them then the only thing I can do is smash the horn into pieces with a hammer to remove it from the opening. :anguished:

Isn’t the horn in a rubber grommet in the inner wing like the ‘40? If it is it should just wrangle out, fairly sure they are permanently attached to the filter housing.

This may help? Note that there are a couple of “buttons” to press in order to unclip the horn from the pipe.

https://www.sngbarratt.com/uk/#!/English/FindParts/Families/XJS/7/38/11007/11170/11153/1/10/1/viewassembly/8381/:AIRCLEANER-4.0%20LITRE

Frankie

I think you have to compress the horn top and bottom just at the back side of the radiator assy. IIRC there are two lugs on the top side and two on the bottom side that need to be clear of their retention lugs in order for the horn to slide towards the rear

Thanks guys. Yep, I found those buttons (on top, didn’t see the pair on the bottom) shortly after I posted that. I went and crawled right up on top of things and shined a bright light down on the horn/intake and spotted them, although at first they looked to me like those slotted fasteners Jag uses that you turn with the edge of a dime or something to fasten/unfasten. :pensive: I basically just took my slotted screwdriver and pushed down on each of them, one at a time, while yanking backward hard on the air horn. Geez, what a way to attach/mount something. :roll_eyes:

btw, the thermostat r/r went well, and sure enough it looked like the original thermostat was in there and therefore was presumably stuck open. The Fail Safe replacement works great. I can actually see the engine temp now climb until it gets to just past the “N” and then suddenly drop just below the “N” when the thermo opens. Since originally Superblue’s thermo was not doing that, I should have realized from that alone that the thermo was stuck open ever since I bought her. The only downside is that my heater still doesn’t seem to blow that hot, but then maybe the facelift 4.0s are like that (?) Or, possibly my heater core needs a backflush … :confused: Anyone know what the temp should be at the dash vents with the heater knob fully clockwise and the speed set at lowest?