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Jag-lovers - XJ40 Common Problems

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   XJ40  Common Problems

by Bill Weisman   back  back to Modern home page 

Related Pages :

The  "What goes wrong with these cars"  page
- originally written by Bill Weisman -

This page can tell you not only what to look out for an on XJ40, but also what to look for to some degree on an X300 as the cars are quite similar in many ways.  I ought to stress that the X300s are far, far less problematic and trouble-prone as some of the XJ40s can be.  But I have seen a couple of neglected 1995 XJ6s out there, and it ALWAYS pays to check any Jaguar out.  Bear in mind, repairs for these cars ARE expensive if you take them to a dealer...... Happy (head)hunting!!

aj6cutout.jpg (14436 bytes)This is the Jaguar AJ6 Engine, as fitted to nearly every XJ40 Sedan. (What, you think I was gonna put a Toyota engine up here or something?)

This page is to give you a bit of an idea of what these cars can put a prospective victim, er, owner through. XJ40s are either money pits or joys. If you know what you're dealing with, they are the latter. It's also important to note that this is more of a "What can go wrong with" page, not a how-to fix them page.  For repair info, please scroll down and follow the link to the XJ40 Book Index.



OK, well, most of the XJ40s that I have seen haven't been too terribly rusty, nonetheless, they seem to rust quite a bit more than their competition (I have yet to see a 91 Lexus with rust, but I am sure I will get E-Mail about this!) Well then, let's start at the front of the car.

First, the hood (bonnet) likes to rust not only at each corner, but also under the front lip by the headlights, it's a bugbear to see, but they will rust there. Also, be sure to check the front subframe where the suspension's upper A-arm mounts to the subframe (aka crossbeam) these have a habit of rusting out, this is quite serious! I found out that mine failed when I had better than 3 degrees of negative camber on the left front wheel! Moving further back, you will want to check the windshield mounting areas for bubbling, as well as the outer doorskin, especially close to where the HVAC vents go through to the doors. Also be sure to check the bases of the A-Pillars. I once saw a 1991 Sovereign at a dealer in Pittsburgh with badly bubbled A-Pillars. The tinworm also likes to hide in the rocker panels, jacking points, and especially under the fuel filler flap. Also be sure to check under the carpeting in the trunk (boot). While most XJ40s that I have seen have rust in the boot, it's surface rust 98.623% of the time. As far as integrity of the body goes, these cars are fairly decent, although I have heard reports of the sunroofs leaking while the car is parked at a slight incline.

On the early XJ40s (88-89 Model Year) the door handles are notoriously prone to failure. There is an updated design, but don't expect miracles unless you own a 90-94. This is one of the most common failure points on these cars. Sadly, these, like most parts on these cars, are rather pricey to fix. Also, curiously enough, the taillights tend to be easily shattered when the trunk is slammed, so close yours like a normal person!!! <G>


Hmm, bet ya were waiting for this part, eh? Heheheh, good ole Lucas electronics.. WRONG! Actually, Lucas tends to get a bad rap, but I have my own opinion. Jaguar tells Lucas that they want, say, a Fuel pump, but they want it for $50, so, Lucas gives them what they want. Actually, on my 1988 Daily driver I have had problems with the Hella (German) Overcharge relay for the ABS, the (German) Hirschman Antenna. Also, the (Japanese-Made) Air Flow sensor, but that was my fault because I dropped something on it.

OK, here's the problem areas that I read about, hear about, curse about, and pay for. Bulb Failure Modules seem to be a problem on the 90+ cars, the car thinks it has a blown bulb, but it doesn't. This is something that, personally, I live with on my 1991 Sovereign. Big fat hairy deal, A little orange bulb glows on the dash, is it worth $200 to fix? Not to me. Oh, this is important.. ALL SEDANS WITH AUTOMATIC SEAT BELTS ARE COVERED BY A LIFETIME WARRANTY ON THEM, SO DON'T PAY TO FIX THEM!!! Now you know, and education is priceless, eh?

Ahh, on to the AC Control panels, these like to break, but when they do, the system is dead. Remans are available, but.. Rumor has it that it's a microswitch that turns the panel on and off. This is easily fixed if you know how to do electronic work. Many Thanks to Jim Schultetus of Coventry West in Springfield, Illinois for telling me about this. The AC Computers themselves also like to go out, when they do, the car will not blow AC out of the center vents. Be sure to check the door locks, these often fail and when they do, it's often a lock solenoid, but this can cause the whole system to come crashing to a halt. For some reason, I commonly see working systems with the exception of a rear door lock, this is a problem because the rear lock knobs are located at the rear of the doors by the rear door handles making it quite difficult to reach around and manually unlock them.

Gauge clusters on the 88s and 89s can act up, especially the odometer, it simply stops adding mileage, whether this is a good thing or a bad thing is left up to you. I have also heard of some of the 1990 and 1991 cars having problems with major inaccuracies of the trip computer, this is fixed by spending lots of money on a new trip computer module. Also, early cars tend to have power seat motor problems, this too was improved on the newer cars.


The driveshaft carrier bearings frequently go out, these cost about $90 or so to replace from what I am told. This will cause a vibration when you let off the gas. Differentials like to eat up their bearings, oftentimes, a reman unit must be fitted at an approximate parts cost of $650+. Engines and transmissions are extremely robust, the transmission is the ZF 4HP22 (I think.. feel free to correct me) which is found in many premium European cars and is a very proven design. The 3.6L engines do suffer from head gasket oil leaks. common is a leak by the distributor. From what I gather (my 88 has this problem) this is one of those "you can live with it" deals.

On my 1988 3.6L the head gasket is leaking, but, it's not affecting the compression, and water and oil do not mix. As far as I am concerned, I will live with it as it's not a cheap thing to fix. It must be stressed that overheating this engine WILL severely damage the cylinder head, so don't do it! PS, if you have a low-compression '88, you can use 87 Octane gas, all others need 91 octane.

Mileage isn't a problem on these cars as it can be with some of the XK and V12 engined Jaguars. I know of one with 220K on it, and another with 160K on it (a pic of the 160K car is on one of these pages). The design of the AJ6 engine is superb, and the durability is exceptional. So, if you find a well-maintained 4.0 car at a great price, and the only thing wrong is an odometer that says 120K, I wouldn't let that stop you provided that it has been properly serviced.

Suspension and Brakes

Perhaps one of the biggest problems on these cars is the hydraulic rear suspension. These are quite trouble prone to the point that Jaguar ceased installing them on 1993 and newer cars. This system automatically levels the rear suspension under load. If you have any 88 or 89 XJ40, it has the system. From 1990-92, the base XJ6 was not equipped with the system, but the Sovereign, Vanden Plas and the Majestics were. When the self-levelling suspension is working properly, it's an excellent system, when it fails, the rear of the car will bounce up and down as if the vehicle had it's shock absorbers removed. The best course of action is to install a conventional suspension retrofit kit from Jaguar. This is not too tough to install, and can be had for about $450. KYB also makes a retrofit kit but, from what I have been told, it's hardly an improvement over a failed hydraulic suspension. Something about springs I think. I have seen the KYB kit go for anywhere from $225-300, so the preferred Jaguar kit really isn't that much more $$.

Otherwise, the rest of the suspension isn't a major problem area on these cars, upper A-Arm bushings tend to get weak with age and miles, and renewing these can make the car feel "new" again, also be sure to check that the boots on the steering rack aren't filled with fluid, this means imminent failure of the power steering rack.

If you skipped what I said earlier about the front subframe, here ya go: The front subframes can and do rust out where the upper A-Arms mount to them. This is a serious problem, and it is preventable by drilling holes in the bottom of the subframe, allowing water to escape. What happens is the subframe is a sealed box section, water sneaks in, can't drain out, and rots it out from the inside. Obviously this is a pretty serious problem.

Ahh, on to the brakes! The braking system on these cars is excellent, but it must be properly serviced, oftentimes an overdue (fluid should be changed with DOT 4 annually) fluid change will bring the system back to health in regard to slow to extinguish pressure warnings and the like. Also, these are heavy cars, and as such they're pretty hard on their brake pads and discs. Plan on replacing the rotors whenever you do a brake job. "Slapping pads" is not a good idea. Also, Anti-Lock-Failure warnings are oftentimes the result of two simple problems. First, on the early cars (and maybe the later ones, I dunno..) the system won't work if the overcharge relay in the trunk has failed, on the 88s and 89s, this is located on the left side of the trunk, it's a kinda tall Hella relay, and the contacts on the circuit board can act up. Resolder them and your ABS may again live! Also, on higher mileage cars, the ABS speed sensors can get gummed up with brake rotor filings, a good cleaning will often nurse these back to functionality.

Tires and XJ40 specific stuff

One thing that bugs me is how often I see these cars with cheap or crappy tires on them. The 1992 and older cars use 205-70VR15s, a size shared with many Minivans, Cadillacs, Lincolns, Chevies, etc. However, only the Jaguars use a "V" rated tire in this size (149 MPH), therefore, Roadhandlers from Sears don't belong on these cars because they have a Cadillac speed rating (usually S or 112 MPH). Now, many of you may be saying "But Bill, I'm not gonna go 149mph! I never go over 75!" Great! Going 140 mph on public roads will have the highway patrol taking a buzz-saw to your license! However, it's not about speed.

The reason that these cars have these tires is because they can go pretty damn fast, but in reality, these are performance tires, and keeping the original equipment-level tires on your car will keep it driving like a Jaguar, I mean, if we wanted our cars to ride and handle like Minivans, well, then we'd probably drive minivans, right? The only tires, to the best of my knowledge, that properly fit these cars (for sale in America...) are the Pirelli P4000 SuperTouring (What I have on my car, excellent choice, and these are the replacement for the P5), The Bridgestone Turanza V, The Michelin MXV4 and, if you can find them, the Avon Turbospeed CR28. In other words, Aquatreads might as well be the wrong size.

Now, on to other XJ40 stuff, these cars use a special fluid for the Power Hydraulic system. Prior to 1990, the reservoir supplies the SLS rear suspension and brake booster system, and with 1990 and later (fitted with Teeves ABS), the SLS rear suspension (where fitted) and power steering. This fluid is called Castrol HSMO (Hydraulic System Mineral Oil) and you usually have to go to the dealer to get it. It's yellow-green in colour, and should not be mixed with regular brake fluid (clear) or power steering (red).

And, what about wire wheels?  Personally, I think they look good on Mark 2 3.8s, E-Types, XK150s and the like.  I think they look disgusting on XJ40s, and, with the exception that some people like the appearance, they serve no positive benefit to the car.  They cause all kinds of vibration, air leaks, they need to be retorqued on a regular basis (bet ya didn't know that!) and they hurt the handling of the vehicle.  Also, Neither Jaguar Cars or Jaguar of North America likes them.  Jaguar's position was something along the lines of "We won't be responsible for any problems caused by these wheels".  Obviously, I don't like the idea of wire wheels, and neither does Jaguar, so, if you want them on your car at least you'll know what you're getting yourself into.

For more info on XJ40 Pricing, Values and model year changes..  Please go to the Buyers Guide.



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