I bought a 1988 XJS with 74,000 miles last Friday that had been driven less than 1000 miles in the last 15 years. I checked the oil and drove it 40 miles to a car show on Saturday morning without problems, incl. Interstate at 70 mph. The temperature gauge stayed right at the top end of the letter N.

On the way home two hours later a different story. The temperature gauge went about 3/4 up to the middle between N and H within while driving 70 mph on the interstate. That's when I pulled into a gas station to let the electric fan cool down the engine. I drove the rest of the way home on slower side roads.

Today, I drove it until warm and then let it idle in the driveway for ten minutes while staring at the temperature gauge. As soon as the temperature gauge gets above the N, the electric fan kicks in and the temperature stays right at the top end of the N. So no overheating while idling.

What should I try first? My Jaguar XJS is supposed to be a cool car, not a hot one.

 

My first thoughts are a clogged radiator. Clogged internally, externally, or both. I'd remove the radiator for professional cleaning.

Actually, since the car is new to you and (presumably) you don't have a repair records, I'd also flush the system, replace the hoses, thermostats, belts, and fan clutch. Then properly bleed the system. Make sure to get correct thermostats.

Do it all, do it right, do it once...and you'll be "good to go" for years.

Cheers
DD

 

I've been dealing with high temps for awhile, when I first bought my car it would go well above N at idle with the elec fan spinning wildly, now I can floor it up a mountain pass with no issue and without recoring the radiator.

Get some Ford VC9 coolant flush to start with and follow instructions to the letter, then follow up with more flushing because it gets worse before it gets better. Your car might have some stop leak in it which needs to be dissolved and removed, at the very least the system is clogged with rust. I'd suggest buying a gallon of Metal Rescue and/or LiquiMoly's radiator cleaning product as well. Installation of a coolant filter isn't mandatory but I strongly recommend it, I've had one for a few months now and it is still pulling grey silt (previous owner's stop leak) out of my coolant.

Also renew radiator caps with OEM Jaguar ones you can tell because they don't suck and actually fit perfectly, I ordered mine from Jaguar and they work. Thermostats to which can be a bitch to find the right size ones. Also ensure the thermo clutch is working and your rad fan isn't cracked to **** like mine was and liable to fly apart at any moment.

I also used a shop-vac to suck the coolant/water our via the inlets on the rad on several occasions during the flush(s) you want to backflush with sufficient force to dislodge any crap in the rad and a shop vac is the fastest way to do so.

 

I'm in the process of dealing with over heating.
My cat is overheating if the needle goes any above the bottom of the N, if mine was registering where your needle has been my engine would be toast.

Before taking the rad out, go underneath take the spoiler, the metal shield off, you will see 2 large phillips head screws one on each end at the bottom of oil cooler, take these out, wedge between oil cooler and radiator, be sure not to touch the radiator or oil cooler fins while wedging. You will be able to separate about 3/4 to an inch, take drop light and look up in between the rad and evap for trash if you see any take a fly swatter the handle end that has the metal loop, stick it up there move back and forth till trash falls down. After cleaning take your shop light and place it between fan and radiator, from the front of the car look thru the evap fins and see if you can see light clearly, if not only then would I take rad out as it is a job.
Mine had a tiny bit of debris and I could see light thru fins clearly, at this point I took bottom rad hose off drained coolant, take both air filter canisters off remove hoses from thermostat ports, take out thermostats, have a friend hold palm of hand over passenger stat port while you put water hose and air hose in driver side stat port and flush engine a few minutes, do the same on passenger stat port. Put water and air hose in passenger top rad hose and friend put his hand over driver top rad hose and flush and do opposite top rad hose. This is where I'm at right now. Next I will reconnect all hoses leaving out the stats,I have 2 bottles of Prestone rad flush one bottle will do 12 quarts so I have 2 bottles as cooling system is 21 quarts, follow the instructions. Start engine,after it reaches running temp I will let idle 10 minutes accelerating now and again. I will then remove bottom hose drain and remove the other hoses as I did before and repeat as I did before with water hose and air hose. Then I will install new stats, put all back togeather, add 21 quarts of coolant, bleed or burp the system, start engine and cross my fingers.
Be sure to put air breathers back on and connect all air hoses before starting. I did not do this had car on ramps and was going to back it down out of my shop to flush so not to get water all over shop. When I started and put in gear engine reved so high that with brakes on the rear tires were spinning, It went down the ramps quicker than I wanted. LOL

 

First of all, welcome to the community! You are in the right place. And you are absolutely right -- it is a very cool car!

A lot of us are very mindful of engines running hot. Myself included.

Just like mdi, i would probably not risk driving with the temp gauge at the very top of the 'N' or above. My temp gauge stays at the bottom of the N when on highways, but was creeping up to top of the N in traffic during hot weather.

So, I am currently undergoing similar steps outlined by V-XJ6. I thoroughly flushed the old coolant (was all dirty and not very green in color) and I also replaced the thermostats. Took the car for couple of loops in the neighborhood, but not for very long. Next weekend will do a longer drive, including areas with stop lights and traffic, to see how the car behaves.

If I see temps creeping up higher than I am comfortable with (top of the N), will undertake next steps: flushing the rad again simultaneously with getting additional gunk out and other steps proposed by the gurus.

These cats are high-maintenance animals But some people like them for that

 

I have a 94 XJS 4L and on hot days w/ A/C running, my temp gauge will go to slightly above N, and if I'm not moving (at stop light), it will creep up to between N an H. So far, this hasn't caused a problem

 

And it probably never will....but it depends on how quickly the temp increases and if it would keep climbing-climbing-climbing if you didn't start moving along again.

Cheers
DD

 

This is why Jaguar eventually threw in the towel and joined the ranks of others by fitting temperature gauges that read "Normal" over a rather broad range of coolant temperatures.

Anyhow.....

I would suggest using one of those infra-red thermometers to get an idea of actual temperature. I take the reading at the thermostat housing. It might put your mind at ease. Or, maybe not.

Ages and ages ago some of us (on another forum) compared results and the difference was dramatic. On my car the bottom/middle/top of the "N" corresponded to 180-190-200ºF ...which seemed to be typical and logical....but some others reported much lower and much higher readings, as much as 20ºF difference. The gauges are that flakey.

But, to beat my usual dead horse, the coolant temperature is only one part of the picture....and, IMO, not the most important one, within reason of course. Coolant FLOW to all areas of the engine, especially the cylinder heads, is what's most important. This requires a very clean and properly bled cooling system.

You can keep the coolant temp at the bottom of then N or lower all day long and still cause damage of the coolant isn't flowing where it should. Or you could run forever at the top of the N or higher and do no harm whatsoever if you have good flow.

IMO, flush the system thoroughly. Have the radiator professionally cleaned (just DO IT!). Make sure all the little vapor pipes and hoses are clear. Bleed the system until you are 110% confident that all the air is purged. With these steps you can be reasonably confident that you'll have good flow and you won't have to worry so much if the temp gauge ticks upwards a bit.

Of course if coolant temps rise with no end in sight and/or during moderate ambient and driving conditions you may have other issues to investigate.


Just my 2-cents!

Cheers
DD

 

I know, a 4.0 six cylinder engine would probably be easier to maintain. But XJS with a six cost a premium here and are rarely available locally, so another $1000 for shipping. Hey, this calculation leaves me with about $3k to get this V12 in shape. :-)

Plus I love that V12 grin on my face when I put her in first gear and keep the pedal to the metal til 60 mph before shifting into second gear and looking for cops. When she is not overheating, she goes like Angelina Jolie.

 

That's the spirit ! Plus, you don't have to worry about carbon build up

Cheers
DD

 

I had this exact symptom with my XJS when I bought it.

After removing the radiator and having it re-cored, I did this because it was not much more expensive than rod cleaning. It was good on the highway and was like this for a couple of years.

Then it started to getting warm in traffic. So I installed electric fans. I also did thermostats, hoses and stainless crossover and header tank while I was there. This is now nearly 7 years ago and my car has not overheated since and this is with regular driving in 40°C temperatures with AC on.

Where the temperature gauge needle sits on the gauge will vary from car to car, due to a number of factors.

Temperature sender tolerance which will be a few %
Battery voltage as the gauges are NOT fed by a regulated voltage.
Gauge itself also has a tolerance due to the components that drive the needle.

I broke the spade terminal off the temperature gauge sender, the new one I bought had the gauge sitting higher than the original one with NO OTHER changes.

The gauge needle will vary, what is important is that the engine does not boil its coolant

Oh and I forgot to add also replace the caps with the correct ones.

 

My plan is to get the radiator unclogged and working first. Even if that solves the problem, I plan to replace the water pump, thermostats, electric fan switch, hoses and a few other things later this year, so the engine will run another 30 years.