Jaguar XJ-S. Manual - part 55

 
 

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It’s plausible, though, that the goo make break down with time or mileage.  Typically, a highly viscous fluid has long 
molecular chains, and subjecting such a fluid to shear gradually breaks those chains and makes the fluid less viscous; 
this is one of the reasons you change your oil regularly.  If the same thing happens to the goo in a fan clutch, it may lose 
its effectiveness as mileage is added up even if the seals remain intact.  Ed Sowell says, “I am a great fan (no pun 
intended!) of changing the clutch. It had a very good effect for me, even though there was no external evidence of mine 
being worn out. It is my opinion that the commonly cited fan clutch tests are meaningless.” 

 

OPERATION -- 4-BOLT CLUTCH:  The later 4-bolt fan clutch is a thermostatic type, meaning it engages more 
firmly to blow more air when the air coming through the radiator is hot.  As opposed to the simple 1-bolt fan clutch, 
this thing is remarkably complicated.  It functions by having a chamber at the front, divided from the driving impeller 
by a panel.  When the engine is cold, two thermostatic elements -- one obvious coil on the front and a simple bimetal 
strip inside -- conspire with centrifugal force to move the goo out of the impeller area and into this chamber, thereby 
largely disengaging the clutch.  When it gets hot, the thermostatic elements allow the goo to move back into the 
impeller area, providing a firmer engagement and faster fan speed. 

 

FAN CLUTCH CHECKING -- 4-BOLT CLUTCH:  If the problem isn’t obvious (totally seized, freewheeling, etc.) it’s 
very difficult to tell when a thermostatic fan clutch is bad.  How it feels when turned by hand depends largely on how 
hot the clutch was when the engine was last turned off, since the goo won’t move from chamber to chamber when the 
engine isn’t running.  Just playing with it when cold can move some of the goo around, causing it to change feel while 
you’re studying it.  Reportedly the best indication the clutch is bad is that the car is running hot in stop-and-go traffic -- 
although, obviously, that might be caused by any of several other problems.  Typically it’s when the owner can’t find 
the problem and replaces the clutch in desperation and the car quits overheating that we learn that the clutch was bad. 

The thermostatic clutch may be complex, but it still involves thick goo -- and therefore the goo may be subject to the 
same molecular breakdown as that described for the 1-bolt clutch above.  Hence, it may make sense to replace it every 
x miles (perhaps every 60K miles or 100Km) whether it looks bad or not. 

Of course, if the clutch is completely locked up, it’s shot.  This is often the result of a bearing failure; the 4-bolt clutch 
has a single ball bearing in it.  Some people are tempted to continue driving with a seized fan clutch, because it moves 
so much air and keeps the engine cool.  However, it is not recommended for three reasons.  First, it makes a lot of 
noise.  Second, it uses a lot of energy, enough that you will be able to notice a drop in fuel economy if you’re following 
the numbers closely.  And third, if it’s the plastic fan, it’s likely to come apart since the fan will be turning a lot faster 
than it is intended to.  When a couple of plastic blades bounce off the bottom of your hood and leave a nice dent, you’ll 
wish you had sprung for a new fan clutch. 

There is, believe it or not, at least one more failure mode of this fan clutch.  Marty Sullivan had the bearing fail in his 
fan clutch so it didn’t hold the fan centered properly.  At highway speeds the unbalance vibrated the entire car.  This 
was tricky to diagnose since it looked OK when the engine was off and felt OK when turned by hand; it was only by 
watching it wobble at idle you could figure it out.  Of course, this problem is likely to damage the fan support bearing if 
not corrected quickly. 

The difficulty in determining whether a fan clutch is operating properly is just one reason why replacing the belt-driven 
fan with an electric fan as described on page 219 makes sense.  You can easily tell when an electric fan is operating 
properly. 

 

FAN CLUTCH REPLACEMENT:  If it is determined that the fan clutch is a problem, there are several possible 
courses of action: the fan clutch can be replaced with a new one; it can be replaced with a substitute; or the entire 
belt-driven fan scheme can be chucked and electric fans installed.  Your local parts shop is unlikely to carry a 
Jaguar fan clutch, so you will have to consult a Jaguar parts supplier (and spend some serious cash) to exercise that 
option.  Substitutes are discussed below.  Replacing the belt-driven fan with an electric fan is discussed starting on 
page 219. 

 
 

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Of course, you could bolt on a fixed or flex-blade fan and eliminate the fan clutch altogether.  However, this results in 
slightly worse fuel economy and a considerable amount of noise (whine).  Most would consider the noise unacceptable 
in a car such as the XJ-S. 

The electric fan is probably the best overall solution, and will result in better fuel economy and more power.  There 
may be slightly more noise at idle (depending on the fan you use), but much less noise at higher RPM.  It is unknown 
why Jaguar doesn’t use this system to begin with; perhaps they don’t like the sound an electric fan makes.  Or, perhaps 
they wanted to minimize the use of Lucas and Bosch components. 

 

FAN CLUTCH INSTALLATION -- ONE-BOLT TYPE:  Graeme Adamson says, “I replaced the fan clutch several 
months ago.  Having done it one before, I figured I was an expert.  Only problem is, second time round, I didn't fasten 
the nose bolt tightly enough, nor did I use Loctite on the thread.  As a result, I was driving home one day when I heard 
a "clatter clatter" sound.  Switch off real fast, but the damage was done - the bolt had come out and fallen down the 
shroud, and the fan and clutch had spun off into the radiator. 

“As it happened, the clutch was fine, I happened to have a spare fan, and I had to pay to have the radiator replaced.” 

 

FAN CLUTCH INSTALLATION -- FOUR-BOLT TYPE:  Dan Jensen suggests that, when reinstalling the fan 
clutch, “Use nyloc nuts on the fan-to-pulley studs.  It is a real pain to install both a lock washer and nut on the end 
of the four studs with very little clearance.  Having just a nut to worry about dramatically lessens the problem.  I 
have never had them come loose in any of my three Jags.” 

 

FAN CLUTCH SUBSTITUTION -- ONE-BOLT TYPE:  The early XJ-S, from introduction through 8/79, was fitted 
with a fan clutch, part no. T55C, with a single bolt on the front to hold it on.  These also used a metal fan blade, 
C39831.  

Mike Morrin notes:  “The early XJ-S fan clutch appears to be identical to the unit used on a Rover 3500 SDI.  This 
might not be very helpful in the USA, but they are relatively common in the UK and some other countries.  When the 
fan clutch on my XJ-S was found to be seized, I bolted on the Rover part (no modifications) and have had no problems. 
 The Rover plastic fan is different to the Jaguar’s.” 

It might be possible to retrofit the later type clutch EAC4751 and plastic fan EAC3265 (or the substitutes suggested 
below) to the earlier XJ-S by purchasing the pulley EAC3438 and the bearing EAC3437.  You might also need bushing 
EAC4382.  The question is whether or not the bearing housing is the same, or will at least position the fan properly. 

 

FAN CLUTCH SUBSTITUTION -- FOUR-BOLT TYPE:  Later XJ-S’s used a fan clutch that mounts with four bolts 
to the front of the drive pulley.  This is the prevalent style on US automobiles, leading one to consider the possibility of 
low-cost substitutes.  However, the fan clutch market is full of niggling little details, so one must check several 
dimensions carefully to make sure a substitute will fit: 

 

A) 

The pilot hole in the center of the shaft must fit snugly around the stub in the center of the mounting 
flange.  A hole too small won’t go on, and a hole too big won’t center the shaft properly. 

 

B) 

The mounting bolt pattern must be workable.  This generally isn’t too critical, because they all seem 
to use four bolts and the aftermarket clutches provide radial slots to fit nearly any pattern. 

 

C) 

The shaft must be of comparable length.  Too long will press the fan into the back of the radiator.  
This dimension doesn’t need to be exact, merely close enough to prevent interferences and keep the 
fan within the shroud for maximum efficiency. 

 

D) 

The bolt pattern for mounting the fan to the clutch must match. 

 

E) 

If the fan has a recess for the clutch housing, the clutch housing must fit within the opening. 

 
 

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The auto parts houses normally have a cross-reference chart that lists the above dimensions for the fan clutches 
available.  If you compare the clutch from your car to their chart, you can determine what can be used. 

If you find a clutch that is suitable except the pilot hole is too big, it would be a simple matter for a machine shop to 
fabricate a bushing to adapt.  Some Jaguars come with such a bushing, EAC4382; perhaps this bushing can be used to 
adapt an aftermarket clutch.  Its ID is 5/8”, OD is 3/4”.  Michael Neal suggests you be sure the bushing is correct and 
necessary before pressing it into the clutch, since it can be difficult to remove. 

David M. Johnson found a substitute, a Hayden 2747.  “This is a Ford/GM heavy duty clutch, all the dimensions match 
except it is a little longer, i.e. the clutch bolts on directly with no modifications.  The existing fan will bolt directly to the 
clutch.  The advantage of this clutch is that it will turn at 90% of the pulley RPM.  The standard duty units only turn at 
75% of the pulley RPM.” 

Now, if you have replaced your yellow fan with the later design black plastic fan -- or wisely plan to (see the section on 
fan cracking on page 214) -- Johnson has bad news:  “The two fans (yellow and black) are interchangeable if you have 
the original Jag fan coupling.  The GM fan coupling I stated was a replacement only works with the yellow fan because 
the centre boss is a larger diameter (approx 7.5 inches).  The black fan is OK with the jag clutch coupling, but will not 
fit the GM fan clutch substitute, because the black fan centre boss is only 6.5 inches diameter, i.e. the GM fan clutch 
fouls with the fan blades.  I went out this weekend in search of a clutch coupling for the black fan, but cannot get an 
exact match with the Jag original, because all the ones that fit the bolt holes and centre boss are more than 6.5 inches in 
diameter.”  Understandably, the original style fan is no longer available, so obtaining a new one of the crack-prone 
design is not an option. 

Of course, another option would be to find a fan from some other car and make it fit the clutch and the car.  One 
possibility: the XJ6 fan!  This fan looks just like the original white XJ-S fan, complete with the hub that provides 
enough space for a substitute clutch, but the OD is larger -- 17-3/4” as opposed to the 17” fan used on the XJ-S.  So, 
you’ll have to trim 3/8” off the tip of each blade and then rebalance it. 

Another possibility may be to modify the later design black plastic fan.  The design of this fan involves a plastic 
cylinder with the blades protruding outward, but the blades also protrude inward perhaps a half inch.  It’s these inward-
protruding stubs that cause the interference with the larger generic fan clutches.  Emile Desroches reports that carefully 
marking and trimming these stubs will permit fitting the Hayden 2747 clutch described above:  “I used a Dremel 
"MotoTool" which is a small hand held grinder designed for hobby work and a small circular saw blade, but it can be 
done with a sharp knife or a file if you're patient.  This procedure takes about an hour.  I feel the results (needle well 
below N) are more than worth the grief of the installation.” 

Another alternative for using a non-OEM fan clutch:  You can usually find a way to use whatever fan was originally 
designed to mate to the clutch you are using -- which means you don’t have to restrict yourself to clutches with the 
same fan bolt pattern.  A procedure is described below. 

 

1. 

Go to your local junkyard and buy a fan that fits the clutch, basic Ford or Chevy; preferably with 
unequally-spaced blades (reduces whine) and preferably with aluminum blades (easier to cut). 

 

2. 

Trim the tips of the new fan until it is the same diameter as the original.  After cutting, round the 
corners and file the edges for safety. 

 

3. 

Bolt the sucker together and check for interferences.  Noted possible interferences include the water 
pump pulley and an oil line across the bottom.  The oil line may be bent and repositioned, or both 
interferences may be corrected by trimming or notching the blades.  Obviously, trim all blades 
exactly the same way.  It’s helpful to cut out a cardboard template the shape of one blade and use it to 
mark each blade for trimming. 

 

4. 

Remove the fan from the clutch.  Set the fan on razor blades centered on opposing bolt holes to check 
the balance.  Trim a little metal from the blades on the heavy side until it balances.  Rotate 90° and 
balance the other way.  Make sure it balances both ways when completed. 

A fan clutch that has the same pilot hole diameter, a slightly longer shaft length, and a different fan bolt pattern was 
found at AutoZone.  It is made by Imperial, part number 215038.  Since the offset of the mounting flange of the 

 
 

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junkyard-purchased fan was less, the fan blades themselves end up in exactly the same place.  The longer shaft also 
makes it a lot easier to get the mounting bolts in.  It is believed this clutch, with a modified fan from a junkyard, will fit 
all the XJ-S’s from 8/79 on. 

Since the aftermarket clutch was designed to turn a 19” fan while the original turned a 17”, the aftermarket clutch 
engages more forcefully than the original.  This assembly will therefore make more noise (whoosh) than the original.  
But it will reliably keep the engine cool. 

Some aftermarket fan clutches come with a lifetime warranty.  But even if yours doesn’t, you still can replace it much 
more easily next time, since you will already have a suitable fan and/or bushing.  

 

FAN BEARING:  The fan on an XJ-S is mounted on a dedicated bearing instead of on the water pump as in most front-
engined RWD cars.  The bearing appears to be similar to those found in several types of water pump, except the shaft 
on one end is too short to mount anything on.  Perhaps a suitable water pump bearing can be found and the unused 
portion of shaft cut off (be careful not to get the shaft too hot and damage the seals!).  Since finding the bearing itself 
may be hard, perhaps the most expedient procurement method would be to buy a suitable rebuilt pump, remove the 
bearing, throw the remains of the new pump along with the shot Jag bearing back in the box and return it for the core 
refund.  Some rebuilt pumps available in auto parts shops are really cheap. 

A better alternative is to chuck the engine-driven fan and install an electric fan as described below. 

 

IDLER PULLEY BEARING:  The repair manuals indicate that the idler pulley for the fan drive belt is attached to its 
support arm with a nut within a recess on the back side.  On the author’s ’83, the assembly looks just like the pictures 
except there is no nut; the end of the shaft is flush with the surface within the recess.  Apparently the bearing itself is 
not intended to be replaceable; the parts suppliers offer only the entire arm/pulley assembly, EAC8097. 

Bernie Embden reports that the early arms were made of aluminum; later idler arms are iron.  Bernie's car is a '78 (and 
has a nut), so apparently the early design was used at least that late.  Mike Morrin has two early cars and one has a nut 
and the other does not, but both have aluminum arms, so there are apparently at least three configurations:  Aluminum 
with nut, aluminum without nut, and iron without nut.  “The 1980 XJ-S parts catalogue shows the part number of the 
assembly as being C39875, with no separate part numbers for the pulley or arm (and no nut).”  This might be the 
aluminum without nut part number, with the EAC8097 reflecting the change to iron. 

Daniel Pontes had a shot bearing in the idler pulley, and rebuilt the water pump thinking that’s where the noise 
came from.  “This pulley mounts on the water pump so a stethescope is useless.  Disconnecting belts and running 
the engine is also a waste of time.  The only way to track the source is a manual shake with your hands on each and 
every pulley. 

“A few phone calls later I find out that this pulley is very costly and very hard to come by.  Since it is only the 
bearing that goes I thought it should be no problem to put a new one in.  Yea right!!  My fix- 

1. 

find a new FAG bearing  # W52315-1. 

2. 

Have your machine shop press out the old bearing out of the pulley, mark which side faces the 
front. 

3. 

The shaft is only peened onto the arm, it comes out easy enough. 

4. 

The new bearing has a long and short shaft on either side of the outer race.  This is a water pump 
bearing and the shaft is the inner race. 

5. 

Have the machinist chuck the long end into a lathe and dress the short shaft to fit into the idler 
arm. 

6. 

Press the pulley back on with the front side facing the front. 

7. 

The goal is to get the pulley as close as possible to the arm without rubbing.