We noticed the radiator fan has been running after stopped, for about 1-2 minutes, for the last 2 weeks. Temp gauge has been dead center.

Just got back from a 1,000 mile trip, everything was fine.

Next week, we drive 100 miles, but when we stop the temp gauge goes up and up to the red zone. We start moving again and the gauge drops to the normal , mid mark exactly. When we stop again , it goes up. I turn on the heater and it helps while stopped in traffic.

Both hoses on top from the radiator to the block are warm and hot. The electric fan does cool the car in about 4 minutes after stopped.
I'm guessing thermostat, or water pump. Any ideas or tests I could do?
Thanks,

 

https://www.jaguarforums.com/forum/s...ad.php?t=87243

I had a similar situation. This possibly sounds like a lazy thermostat, based on the coolin fans running after shutdown.
I would not know how to rule out water pump as the cause.

Replacing the thermostat is a cheap and relatively easy fix.

I hope the link helps. Lots of great info on the forum search regarding thermostat replacement.

Thanks-
Mag

 

Also had the same issue this past week... in my case it was a broken coolant crossover. The plastic inside breaks and doesn't allow the coolant to flow through the radiator and engine correctly (most of it just keeps cycling through the engine). From what I hear the plastic failing is common on these parts.

https://www.jaguarforums.com/forum/x...ine-off-89439/

If you buy a new crossover assembly, it comes with a tstat, seals, and new temp sensor.

 

Same thing happened just last week... Jagbits.com came through with the parts cheaply, though. Car is running smoothly.

 

It was a broken plastic housing and thermostat. No way to tell which one failed first. $350 parts, plus $250 labor.
Big kudos to San Jose British Motors in San Jose, CA - they squeezed me in without an appointment, on President's Day - and were finished by noon! Thank you Glen and Gary!

Only 62k miles. I don't say this often, but what a terrible Jaguar design to use a PLASTIC part for thermostat housing that costs $180. Just a shame. My old 76 Chevy used a $5 cast iron housing that would never, ever fail.
Honestly, from what I've read, I'm surprised this is not a recall, or free TSB retrofit.

 

Yes, it's a very poor design (in my opinion). Seems a lot of the Euro car makers like to use thermoplastics in their cooling system parts, all have similar issues. And at least if the Chevy tstat fails, you can pull it out and the car will just run cold, whereas the Jag will still overheat because coolant doesn't get directed through the radiator.

At least you got yours fixed quickly! I brought mine to the dealer Saturday (under warranty), still waiting...

 

so, similar problem here, it heats up when we slow down, we removed the thermistat from its housing which, it had broken, and put the mostly in tact housing back so it could run but that even didnt help the overheating. whats the crossover look like? this is, very much an irritating problem. cant wait to have it fixed. are there any better after market ones out there? maybe something with a better construciton and not of plastic? forgive me thats a dumb idea its just a bad design overall...

_________________________
2006 XJ8 base
128k miles

 

Just a note in only overheats after driving for a long way... they when you stop it decides to overheat

 

The housing is plastic, & needs replaced with thermostat.
The water pump is right there, with belt, tensioner, & idler bearing.
Along with any suspect hoses, & fresh coolant.

 

a new thermistat and complete tube monster is coming in, in about two days, maybe three. so we plan to replace it. that said i do wonder why the car would overheat with no thermistat at all, and just the housing... thats the confusing bit. its really given us trouble in that reguard. is there any explanation of what else could be causing it? thers no coolant leak, theres no bad hoses, we had even replaced the expansion tank. at this point its getting beyond what we could tell is the issue... this isnt making sense. i thought with no thermistat it would be running cool, it seems to have had no effect in pulling the thermistat.

______________
2006 xj8 base
128k miles

 

Post #17 may help in https://www.jaguarforums.com/forum/x...ine-off-89439/

 

See mhamilton's explanation in Post #6 of this thread.

By the late '90s vIrtually all of the luxury-performance brands had begun using plastic cooling systems, camshaft covers, etc. to reduce weight, because they had to meet ever-stricter Corporate Average Fuel Economy (CAFE) standards, as well as emissions standards that, in the U.S., are primarily driven by the California Air Resources Board (CARB).

Cheers,

Don

 

Well yes I understand the plastic thing.... But that doesn't indicate why it would overheat if the thermostat were removed and the pipe was running wide open. Fans are working water is clean, no leaks, The thermostat is now gone, not there at all. All broken pieces have been removed so it is as if the thermostat was wide open and could never close. Any ideas why it would still be running hot with fans full tilt. Could it be that it's just the temperature sending unit? If the thermostat fails closed then it will be hot forever but most thermostats fail open. But in any case it doesn't matter because it's removed. The radiator pipe is hot and so is the radiator (as it should be after driving for an hour) so I'm pretty sure water is being directed through the radiator. And it only overheats after running for a long while and then stopping. When driving it stays normal temperature.

 

Probably everyone here knows what a "basic" thermostat housing used to look like, and how to replace a simple thermostat.
Unfortunately, the X350 XJ8 plastic thermostat/housing is not "basic", as it has 2 fluid channels (an inner and outer fluid flow). When mine broke, only in the inner channel wall broke - there was NO external sign of failure at all. The result of this design is that the old rule of "just remove the thermostat if it's broken" to keep the engine cool - does not apply. I do know the supercharged version is made of metal, but I don't know if it would fit on non-supercharged engine.

 

AH!!! THANK YOU... Now I understand. Since your post I have been looking at the new one I ordered and I see the overlapping section you are talking about. The plan is to replace the entire octopus. And if it was brittle enough to break off the tabs of the thermostat housing the rest is probably just as brittle. I will be replacing the entire thing but now I understand the problem. Thank you.

On a side note It appears that I did not properly burp the system. I thought I had the system bled properly but after letting it cool over night I seem to have lost a lot of fluid. It went somewhere not on the ground and I think it was into my heater core. After filling the expansion tank again and going through the bleed procedure again I have not had any overheating issues. Fingers crossed that there is nothing else wrong so that when I replace the entire octopus I won't have any more surprises.

 

You cannot run our engines with no thermostat. Our t-stat is serves two separate functions. It opens one way to allow coolant to circulate in the radiator only (to 're-cool' it), then opens another aperture to allow the coolant around the engine jacket.

 

Glad you have things sorted out, & your Jaguar is running cool again..

 

Jaguar xj8 thermostat has been replaced since then there are no error codes accpet for a cold start every once in a while. as for any updates, i ended up before the repair driving without a thermostat and it never overheated once we made sure there were no bubbles in the coolent system. made a video for anyone whom has this vehicle and has to do said repair. seemed to be a sevier lack of any such content on youtube. thats probably because this is a car with few problems but, it always helps to have an in depth guide on how to do this.

 

Had a long trip through ‘bug country’ where bumper became black with bugs. Pulled into rest area left engine on for 5 minutes or so!

In retrospect should’ve shut it off because car overheated and hose developed a leak! After car cooled down added watered down coolant (Night and no other choice) to make it home. Had several hundred to go! After car was no longer overheated (Aluminum blocks seem to cool quickly.) seemed ok on the freeway, (Until passed someone) then stopped at next rest area to ‘top coolant’ (Reservoir low was all.)

On the way back the battery light was intermittently coming on. After being back it was on shortly after car starting. Battery died & it was recharged but died again next day. This time thought Advance Auto could charge it better but heard nothing for days. Called & they said it’s ‘no good!’ Replaced with NAPA but they wouldn’t honor online price from app!

My guess was maybe the multi-v belt was damaged from car’s overheating & spraying coolant?!? Bought that, new coolant reservoir (Had fail on different Jag before), upper hose and ordered thermostat at mechanic’s suggestion. Rockauto sent wrong one & even manual illustrated wrong one. (Vin is upper “H” numbers so found out thermostat housing looks like 2007 (Like yours) and thermostat parts lists were conflicting so ordered OEM thermostat assembly! (3-5Xs more!) Figured new sensor & all else w/b great! [Mechanic said ALT tested bad so got used replacement w/warranty.]

First drive had to let car idle w-a/c on few minutes. Put in drive & temp went up to just below red. Rolled down windows & set a/c max temp w/min. fan & (on road moving) temp normal fast! Got coolant low message. Considered maybe a ‘bubble’ so let car cool. Then drove a few miles & ‘coolant low’ showed up again.

Mechanic not so helpful. Asked if fan not coming on & offered no help. I’m losing confidence even though used same mechanic for alignment issues & simple repair on previous XF. Especially since mechanic claimed car idled for 2 hours without overheating!

Theoretically everything should be happy. Replaced entire plastic thermostat assembly, reservoir and upper hose, belt, generator & battery.

Can the electric fan go bad if doused with coolant?!? (From overheating like I thought belt was & maybe alternator because all was fine before. I think bugs were covering radiator causing it to overheat!?!)

PS: Your thermostat video helped me get the right part-thank you! Even repair manual shows wrong one!

If you have any ideas or thoughts I’d appreciate it! Can buy used working (guaranteed) fan but not new! The 80A strap fuse ‘looks’ OK. Other spades vin look good also. My XF manual had diagrams & locations illustrated. The 06 XJ8 not so much. Could some connector just have been missed?!?

I appreciate any thoughts.