Jaguar XJ-S. Service manual - part 51

 
 

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Alternatively, you can convert to a single-pass system without modifying the radiator at all -- or even removing it from 
the car!  Rather than removing the partition in the left tank, simply install a tee in the lower radiator hose and route a 
hose from the left inlet (which will now be a secondary outlet) down to it.  Tee the two thermostat outlets together and 
feed them into the single 1-1/4” inlet on the right side; this inlet has been proven large enough to handle all the flow. 

 

ELIMINATING THE ONE-AND-A-HALF-PASS SCHEME -- AFTERMARKET VERSION:  The simplest way to 
fix the OEM cooling scheme would be to replace the one-and-a-half-pass radiator with a suitable single-pass radiator 
from some other application.  It just so happens that one application springs to mind: the Jaguars that are converted to 
Chevy power.  Chevy engines have only one thermostat outlet, so it makes no sense to try to use that one-and-a-half 
pass radiator with it.  Besides, that would result in the Chevy overheating as readily as the V12 did!  So, as one might 
expect, the outfits that offer Chevy conversion kits are a good place to go looking for a bolt-in single-pass radiator for 
the XJ-S.  John’s Cars (page 715) offers two such radiators, one intended for use with a small-block Chevy and a 
“super-duty” intended for use with a big block Chevy.  Either one has plenty of capacity for a Jaguar V12.  Both are 
quite reasonably priced -- meaning they are considerably cheaper than a new Jaguar radiator.  John’s Cars uses exactly 
the same radiators for either the XJ-S or the Series I/II/III XJ6/12 saloons, all years, indicating that the profusion of part 
numbers in the Jaguar parts books all involve minor detail distinctions. 

Note that John’s Cars may also offer radiators -- both regular and “super-duty” -- intended to be used with the Jaguar 
V12 engine, meaning they have the same 1-1/2-pass arrangement as the OEM radiator.  You do not want one of these.  
Make it very clear that you want a radiator intended for use with a Chevy engine. 

Another application also comes to mind: the Jaguars with 6-cyl engines.  The 6-cyl Jaguars, whether they be XK, AJ6, 
or AJ16 engines, all use single-pass radiators.  The radiator from a 6-cyl XJ-S is one obvious possibility, while a 
radiator from a pre-1988 XJ6 should also fit. 

The only question mark is whether or not the 6-cyl radiator has enough capacity to keep a V12 cool -- and that’s a 
serious question mark.  The 6-cyl engines are a bit smaller and a bit less powerful than the V12, so in theory Jaguar 
could get by making their radiators with fewer rows or fewer fins or whatever.  On the other hand, perhaps Jaguar just 
used the same cores for both type radiators and the only differences are in the end tanks and hose connections.  Only 
someone who had both radiators in hand could tell whether the 6-cyl rad is lighter duty or whether it has comparable 
capacity to the V12 rad, and so far I have not gotten any reports. 

Another idea would be to buy (or make) a single-pass radiator designed specifically for use in the V12 Jaguar 
XJ-S/XJ12.  Chad Bolles and Bradley Smith have both blazed this trail, and their costs for a custom-made aluminum 
single-pass radiator actually compare favorably with buying a new OEM radiator from Jaguar! 

Bolles and Smith had to discuss the radiator design at length with the people building it for them -- but you don’t have 
to!  Be Cool now offers aluminum radiators to fit the XJ-S; they are still “custom” in that they are designed specifically 
for the XJ-S and they are not actually made until you order one, but they already have the design on record -- you just 
order the part number of the radiator you need.  Be Cool actually offers four part numbers, all of which end in 082 
which is apparently Be Cool’s indication that it fits an XJ-S.  62082 is the radiator that most XJ-S owners will need; it 
is a bare aluminum radiator for an XJ-S with an automatic transmission.  63082 is the same radiator, except that the 
aluminum is polished (Be Cool caters to the show car crowd, so all of their radiators are available with a polished 
finish).  60082 is a radiator for a manual transmission car, lacking the transmission cooler and therefore a few bucks 
cheaper.  61082 is the manual transmission radiator in polished form.  All of these are single-pass radiators with a 
single large inlet at the top right, since Be Cool would have nothing to do with that silly one-and-a-half-pass idea. 

I know what you’re thinking:  “The Jaguar parts books indicate that many different radiators were used over the years.  
Which one does the Be Cool radiator replace?”  The answer: all of them.  To illustrate, the following are the differences 
in the Jaguar OEM radiators: 

ƒ  The very early cars had the oil cooler supported by the radiator.  However, this is a really horrible arrangement to 

work on, and most owners who get in there find a way to convert the oil cooler mounting scheme to be more like 
the later cars; see page 197. 

 
 

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ƒ  The low coolant sensor was installed in the right front corner of the radiator up until sometime in the mid-80’s, 

then was relocated to the header tank.  Regardless of where yours presently is, it would be a good idea to relocate it 
to the header tank; see page 207. 

ƒ  Up until the mid-80’s, the transmission cooler had barbs protruding from the back side of the right header tank and 

the lines from the transmission were connected by sliding the hoses over the barbs and clamping.  Later cars had 
threaded holes, and pipe thread fittings on the ends of the transmission lines were screwed in.  The Be Cool 
radiators for automatic transmission cars come with threaded holes, which allows the owner of an older car with 
hoses and clamps two options: he can screw standard fittings into the holes and connect up the hoses with clamps, 
or he can replace his lines with the later lines with threaded fittings at the ends. 

ƒ  Sometime in the late 80’s, Jaguar eliminated the hokey drain cock and provided no drain at all!  Be Cool took an 

interesting approach here; they provide a drain scheme based on the early radiators, complete with the cute little 
lever -- but they also provide a rationally-designed drain on the left end of the radiator. 

It’s probably possible to fit the Be Cool radiator to an XJ12, but that hasn’t been confirmed. 

Finally, note that there were apparently radiators with either three-, four- or five-row cores, and owners get very 
concerned about how many rows they end up with when recoring or replacing a radiator.  Well, the Be Cool radiator is 
two-row -- but that only illustrates the shortcomings of this method of specifying a radiator.  With brass radiators, each 
tube is perhaps a half inch wide by 1/8” thick, so a core that is two inches deep can fit four rows.  However, Be Cool 
uses tubes that are a full inch wide and also a bit thicker than 1/8”, so two rows provides at least as much surface area as 
four rows of the tiny brass tubes.  Also, the brass tubes are so tiny and flat that you’d be lucky to fit a fingernail file into 
one, but the aluminum tubes have much larger passages so they are far more difficult to plug up. 

Be Cool guarantees a 20-40º temperature drop over 4-5 row brass radiators.  Just how you’d ever make such an 
evaluation is uncertain, but at least they appear willing to stand behind their product.  By their estimation, this radiator 
should be good for up to 600 cubic inches and 1000 hp. 

As of this writing, Be Cool reportedly does not offer any help in connecting the two 1-1/4” thermostat outlets into a 
single radiator inlet; apparently you are on your own there, although it wouldn’t be a great surprise if they start making 
a suitable accessory.  See below for ideas on making a tee. 

Be Cool’s web site is at 

http://www.becool.com

.  Their products can be ordered through Summit Racing, page 717. 

A few other comments about aluminum radiators:  Aluminum conducts heat better than brass, although the walls of the 
aluminum tubes are thicker than the walls of brass tubes which negates some of that advantage.  Brass radiators are 
soldered together, though, and solder doesn’t conduct heat well at all.  Aluminum radiators are welded together, so they 
are all-aluminum (the mass-production aluminum radiators on some cars have plastic end tanks, but that’s not important 
here). 

Some people also value the fact that an aluminum radiator weighs less than a brass radiator, but to make a fair 
comparison one would have to consider the volume of coolant inside as well as the weight of all the attachments and 
fittings involved; for most of us, this concern is not foremost in our minds at this point anyway. 

Finally, note that an aluminum radiator apparently cannot be rodded or recored, so if you don’t keep your cooling 
system clear of obstructions the next cleanout will involve replacing the radiator again. 

The author will take this opportunity to express an opinion: it may not be worthwhile to run right out and purchase a 
single-pass radiator to replace a good condition OEM radiator, but if the original radiator is done for, anyone paying 
Jaguar prices for a new OEM radiator when new single-pass radiators are available for the same money or less ought to 
have his head examined.  The annual sales of new OEM Jaguar radiators should be zero. 

 

ELIMINATING THE ONE-AND-A-HALF-PASS SCHEME -- PLUMBING:  Whichever single-pass radiator you 
choose, you will need to plumb it up.  Obviously, you need to route the outlets from both thermostat housings over to 
the same side of the car.  A simple pipe or hose supported along the back edge of the upper radiator support is one idea. 
  

 
 

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If your single-pass radiator has two 1-1/4” inlets, one right over the other, you simply need to route one hose from each 
thermostat outlet to them.  When plumbing the two inlets, take care not to create air pockets; having the coolant going 
downhill to enter the radiator might trap air in the hose.  It will probably work best to connect the nearest thermostat 
outlet to the lower of the two inlets.  If you cannot devise a routing that will push air bubbles on into the radiator inlets, 
you will need to provide an air bleed port at the high point where a bubble might get hung up. 

It’s more likely your single-pass radiator will have one larger inlet rather than two 1-1/4” inlets.  Hence, you will need 
to tee your two upper radiator hoses together.  One idea would be to have a weld shop make up an aluminum tee.  
Another idea would be to make a tee out of brass or copper pipe fittings.  And yet another idea is to just have a local 
radiator shop slap together a tee out of standard brass radiator fittings.  Byrnal Haley did this:  “All good rad shops 
stock inlet and outlet pipes for rad repair.  I drew a diagram of what I needed and the rad guy fabricated it from stock 
parts.  You just need to tell him which size pipes to use.”  The result simply couldn’t have been prettier.  You can take a 
look at: 

 

http://www.jag-lovers.org/xj-s/book/SinglePassRadiator.html

 

An improvement on a tee would be to make it a wye for better flow characteristics.  Another idea would be to actually 
make a manifold that reaches across the engine compartment, so you only need short pieces of hose to connect it up.  
And yet another idea would be to create a tank or container of some sort with two 1-1/4” lines in and one larger line 
out; a photo of a racing XJ-S in the May 2000 issue of Jaguar World shows such a tank, and it has a radiator cap on top 
-- and the radiator cap on the crossover pipe has been omitted. 

Coolant filters are still recommended with a single-pass setup, but you now have the choice of one or two filters.  Two 
filters, one connected to each thermostat outlet, has an advantage in diagnostics in that you can tell what crud came 
from which bank.  Also, you may use the coolant filters as couplings to connect radiator hoses together to accomplish 
the routing required for this job.  But using two filters also has the disadvantage that the B bank filter could get plugged 
without the temperature gauge sender in the A bank telling you about it.  Hence, it’s better to go with a single coolant 
filter plumbed in after the two lines are teed together if possible. 

If you are using Gano filters, it’s suggested that you either use two or use one that’s 1-1/2” or larger and step the hose 
sizes up to meet it; a single 1-1/4” Gano would probably be too restrictive for the total coolant flow of this engine.  This 
isn’t an issue with the Tefba filters, though, since the filter elements are the same size, it’s only the connections that 
vary. 

If the new radiator’s bottom outlet isn’t in exactly the same place as it was on the OEM radiator, you’ll need to abandon 
the OEM molded bottom hose in favor of a flex hose -- which is a better hose anyway. 

You’ll probably need to revise the air purge system across the top of the radiator.  If the flow in your new single pass 
radiator is left-to-right, it can stay pretty much unchanged, but if the flow is right-to-left you’ll probably want to reverse 
it and put the banjo fitting at the top left and the air bleed plug or valve at the top right.  Simply exchange the banjo 
fitting with the air bleed port.  You can cut the long metal tube and reconnect it with a piece of 1/4” hose and a pair of 
EFI clamps, making it a lot shorter than it was.  You will also need to figure out how to route the connection from 
under the center radiator cap over to this location.  It may be possible to cut the tube near the tee at the left side and flip 
the whole thing over and reinstall it, putting the banjo fitting at the left but leaving the long tube going across the top of 
the support rail and connecting to the hose from under the radiator cap in nearly its original position.  The short tube 
that originally connected the hose from under the radiator cap to the banjo fitting can now be used to connect the banjo 
fitting back to the tee at the left side with a short piece of hose. 

If you get rid of the one-and-a-half-pass scheme, you can forget about relocating the coolant temperature sensors as 
described on page 176.  The only reasons to do that were due to the differential cooling, which you will have 
eliminated.  Of course, if you’ve already done it, you can leave it alone; for similar reasons, there’s no point in changing 
it back. 

 

ELIMINATING THE ONE-AND-A-HALF-PASS SCHEME -- OTHER IDEAS:  Another option would be to replace 
the one-and-a-half-pass sideflow radiator with a simple custom-made downflow radiator.  This would result in an upper 
header tank all the way across, so the two inlets could be right where they are.  The bottom outlet would probably have 

 
 

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to change; it’d add complexity to try to get the outlet several inches up the left side where the OEM outlet is.  It’d 
probably be easier and better to just provide an outlet at the bottom and use a generic flex hose to connect it to the pump 
inlet.  Flex hoses are usually better in this location anyway. 

Believe it or not, the Series III E-Type used a downflow radiator exactly as described.  It’s not known why Jaguar 
decided to cause all sorts of trouble by providing the XJ’s with the one-and-a-half-pass sideflow radiator instead. 

 

RADIATOR MOUNT BUSHINGS:  The radiator is mounted on four rubber bushings, two at the bottom (C43577) and 
two at the top (C38333).  If you wish, you may replace these by visiting your local discount auto parts store and looking 
through the selection of PCV valve grommets that are usually on a display rack in bubble packs.  There is one intended 
for a Toyota that will serve quite nicely in both positions.  It doesn’t have as large a weight-bearing surface as the 
Jaguar originals, but it’s not made of British rubber either. 

By the way, there are several possible explanations for why the radiator is mounted on rubber bushings, including to 
allow for thermal expansion and to protect the fragile radiator from chassis flex and vibration.  However, one plausible 
explanation is that it is to electrically isolate the radiator from chassis ground.  Since the radiator is largely brass or 
copper while the engine block is aluminum, and the engine must be grounded, grounding the radiator would complete a 
circuit through the coolant causing electrolytic corrosion somewhere -- probably inside the block!  Several owners have 
checked and confirmed that their radiators are not grounded; the rubber mounts, the rubber hoses, the foam packing, the 
fact that the fan shrouds are bolted to the rail instead of the radiator itself, all add up to complete electrical isolation.  
Unfortunately, the heater core -- also brass -- is quite effectively grounded. 

 

RADIATOR OBSTRUCTIONS:  One possible cause of overheating problems is that the outside of the coil or the 
spaces between the fins has been plugged with crud so air can’t flow through.  Since the fins in the A/C condenser coil 
and the oil cooler are coarse but the fins in the radiator itself are much finer, the blockage may be dirt jammed in the 
radiator fins while the condenser and oil cooler still look clean.  One great way to avoid this problem would be to spray 
a garden hose through the radiator from the engine compartment forwards every time the car is washed to prevent any 
buildup.  Unfortunately, the design of the fan shrouds and the tightness of the engine compartment conspire to make 
this task all but impossible, so more likely it’s going to have to be addressed by a periodic disassembly and service. 

Worse yet, Jaguar does a poor job plugging the gaps around the condenser and oil cooler, so really big things like 
leaves get blown through the gaps and into the space between the condenser and radiator (see page 226).  The result is 
often a massive collection of debris between the condenser and the radiator, where it’s really miserable to get to. 

John Bertsche provides a procedure:  “Well, I really didn't feel like pulling the radiator this weekend.  I came up with an 
alternate plan, which may or may not be useful to those of you with my problem. 

1) 

Put the front of the car on ramps.  Take off the spoiler, if you're lucky enough to have one.  Take out the lower 
splash panel/lower center valence, or whatever you prefer to call it, if it hasn't rotted into swiss cheese from all 
the wet leaves that have collected between it and the oil cooler after all these years.  

2) 

After liberal use of Liquid Wrench, use your sturdiest pair of vice grips to loosen the two large Phillips-head 
screws holding the oil cooler to the brackets attached to the frame.  Once they're loose, you can try using an 
actual Phillips-head screwdriver to take them all the way out.  (Ed. note: they’re not Phillips, they’re Pozidriv -
- and using the correct tool may eliminate the need for the vice grips.) 

3) 

Carefully pry (on the brackets, please, not the cooling fins!) the oil cooler away from the radiator just enough 
(about 1/4 inch) to get a straight piece of coat-hanger wire (a foot long or so) up in between the oil cooler and 
the radiator, and gently gently use the coat hanger wire to brush the debris out of the space.  If your car is like 
mine, it will look like the tobacco inside a cigarette (about a carton's worth). 

4) 

Use a blower, like your shop-vac, to blow forward through the radiator (like back-flushing the air flow) to 
loosen any crud that's trapped in the radiator fins.  You can hold the oil cooler away from the radiator a little 
bit while you're doing this with sticks or whatever (again, levering only against brackets, not cooling fins!).