Hi, I am a new Jaguar owner having bought a 1988 Jaguar Xjs V12. It does overheat and I'm talking about the needle goes all the way to the H. I just checked the the thermostats and they are fine, I did replace a leaking heater hose and I need to refill the coolant but what are some other steps I should take to troubleshoot this. While driving down the road at about 50 it doesn't overheat but at idle and park it does. Thanks

 

Welcome,

First and foremost, DO NOT overheat the V12, so don't drive it until you have your cooling issues sorted. The engine is nearly bulletproof if you maintain the cooling system properly. Overheat it and you can turn it into a very heavy paperweight.

Second, there is a 'sticky link' at the top of the page of how to's:

https://www.jaguarforums.com/forum/x...k-links-20089/

Go there and download the XJS book by Kirby Palm:

http://www.jag-lovers.org/xj-s/book/XJS_help.pdf

Read the entire section on the cooling system (when you have time after dealing with your cooling, read the entire book, it's a rather amazing document and you'll find it invaluable going forward).

Now to your specific issues as described, two likely culprits are a radiator in need of re-coring or replacement and/or the fan clutch.

If it's either, then there are several other things you may as well do, while you've got access.

Oh, did I mention that you should NOT overheat your engine again?

Good luck.

 

Thank you, only reason i found that out is i had to drive it home from where i bought it funny enough. I am most likely putting in an electric fan and I hope that fixes the issue.

 

Hi Curtiss

Ditto!

DO NOT under any Circumstances Overheat the V12 Engine!

Having the needle go off the Scale is a No No!

But does She still keep overheating now that you have fixed the Heater Hose?

Maybe that was the problem and you have fixed it now.

 

PLEASE don't make that assumption.

The car is 27 years old, and if you don't know when the radiator was either replaced or recored, you may be asking for trouble masking or hiding cooling issues with an electric fan.

I also don't want to be the bearer of possible bad news, but I'm concerned that if it did this on the drive home from purchase, it may have been chronically overheated which can spell trouble.

If you drop a valve seat in this engine, it can be cost prohibitive for most people to fix (unless you fancy pulling the engine and tearing into it just for the adventure).

There's lots of great people here to help you sort things out, but the bear minimum of joining the ranks of XJS owners is taking cooling system issues seriously.

It's easy to bring it up to snuff, and catastrophic not to.

 

Thanks you and I am not driving it now, I can't afford insurance anyway, it is just a project currently. As for the electric fan I am wanting to get one regardless of wether or not it fixes the problem so I am not making the assumption just going through my checklist of possible issues. I have a feeling it is the radiator but just really hoping it isn't. If it is than Ill just have to get a replacement I guess. Thank you all for the info and don't worry I am not overheating the engine except when testing to see if something I did fixed the issue. My next question would be a good recommendation on where to get a good radiator?

 

Depending on your location and the availability of radiator shops that specialize in re-coring, a re-core of your existing radiator is usually your cheapest option.

Otherwise, you can replace with an aluminum radiator. The BeCool and Wizard radiators fit without issues. The most inexpensive ones offered on eBay do not fit without modifying the transmission cooling connections.

The best deal I came across for the BeCool unit was on the Summit Racing website.

btw, I forgot to ask... is your auxiliary electric fan coming on when it should? Sometimes the relay or temp sensor can be at fault.

 

I'm not sure if it is or not actually, If I remember not it is not. Where is relay and temp sensor?

 

I am working on a similar issue with my electric fan not working. Your relay is the first relay on the left side component panel. Open the hood, look directly above the left front tire and you'll see a fuse box and a line of relays. the relay is the one closest to the front. The temp switch is on the radiator itself, upper left area. If you jump the switch and the fan works you know you've got a bad switch. That was my first test.

 

IIRC some of the above may not be correct for his '88 model. The temp switch is on the pump inlet, and the first relay on the left side is actually not a relay but the diode pack for the fan. I think the relay is mounted on the radiator cover just above the auxiliary fan.

(all off the top of my head so not to be taken as gospel)

 

Thank you for the correction, I am new to the XJS as well and was excited to think I knew one of the questions on here, too quick I'm afraid!

 

Thanks for the info!

 

I have an '88. The relay is under a black plastic cover behind the left headlight. If it's still the original one, it'll be red and cylindrical with Lucas on the side.

Does your horn work? The aux fan shares a fuse with the horn. It's located in a fuse block on the left inner fender. If I recall correctly, it's the white one. Be careful if you decide to replace the red relay. Look at the diagram on the side of it to make sure you have the proper replacement.

Before you go to too much trouble, you might put a jumper in the relay socket to see if your fan works.

 

ok and i checked the fuse and it was alright, ill check again when it stops raining. and no my horn does not work.

 

CONGRADULATIONS!

please look at my thread...
My first Jag... the adventure begins

mine went just above the N and I got all nervous
check the water level every time you are about start the engine
I was having to put .75 to 1.5 gallons in and it does make a big difference...

but mine had 3 pin hole leaks at the top of the radiator...
so I did not have to go through the burp procedure (the holes provided it for me)

there can be a lot of debris built up between the air conditioner condenser and the Radiator best to try and clean that out...

also... make sure your fan clutch for the big fan is spinning your fan while idling and that the little electric fan comes on when the temp needle touches the N ...

now that I have replaced my radiator and some of the hoses...
1) it warms up faster....
2) it hardly ever gets to the point where the electric comes on

I have to force it by running it until warm....
shutting it off... wait a minute, restart it... run it a minute shut it off
run it a minute shut it off about 3 cycles... (stock thermostats)

then it will be warm enough to kick the electric fan on...
I do that now and again (once every other week) to make sure the system is in order for summer

once again WATER... open both caps...
pour in the one on the engine until it runs out the other one...

 

or just unplug the bulit connector to the fan that has the red wire coming from the fan and get a wire and hook it to + 12v

if it does not work...
then trace the Black wire from the fan... it should go to a eye connector that is fastened down with a NUT on the metal
un-connect it and connect it to a known ground -
it should spin then... if not

mine no longer needs the electric fan...
it is for the air conditioner and if the summer stop and go is more stop than go...

oh make sure that the flaps under the electric fan are in place, if they are not it will contribute to overheating while stopped as the air will just loop through the fan and the open holes the flaps close and not be drawn though the radiator

 

The flaps are in place thats not a problem, I still gotta check the fan, its been raining all day so I haven't gotten a 12V to test it.

 

even if the electric fan is in proper working order...
it should not be the primary air handler... through the radiator...
that job goes to the big fan.... make sure that the fan clutch for it is spinning it, when warm....

the two fans are separated and act on their own (or should)

new fan clutch is about 30 to 50 us $

my Fan (Yellow, was cracked... as was pointed out but a nice member here)
and a new upgraded Black fan blade cost about 100
make sure if you have the Yellow fan that it is not cracking...