Jaguar XJ-S. Service manual — part 48

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Another problem is the little adapter, which is steel and therefore subject to corrosion. Craig Sawyers reports, “Mine
was rusted solid inside, and so totally inoperative.” Steve Haley says, “The short metallic slightly conical connector
was completely plugged with corrosion. The hose into the tank crumbled in my hands...and the metal brackets were
rusted and in pieces.”

Yet another concern: The end of the rubber hose inside the atmospheric catchment tank obviously needs to be open,
both to allow coolant out and to suck coolant back in. In some cases, the hose blows coolant just fine, but when
sucking the tip of the hose gets sucked onto the bottom of the tank (or even onto the side, if someone is really unlucky).
It then can’t pull in any more fluid even though surrounded by fluid, so the system pulls in some air from somewhere
else instead -- or starts sucking radiator hoses flat, which is also trouble.

The fix is easy: pull the hose out of the atmospheric catchment tank, and redesign the tip of the hose so it can’t possibly
get sucked onto a surface. One idea is to punch a 1/4” hole through the hose crossways about a half inch from the tip.
This will prevent the hose from sucking up the bottom 1/2” of the fluid in the atmospheric catchment tank, but typically
you’d rather not suck up the dregs anyway.

When fooling with the coolant recovery hose, remember that the hole where it enters the top of the atmospheric
catchment tank is supposed to be airtight so that fluid won’t overflow out that point if the tank gets full.

AIR PURGE SYSTEM: When coolant is added to a cooling system, there is always some air diffused in the liquid.
Over time, this air will come out of solution and rise to the top of the liquid, forming air pockets. To avoid creating hot
spots (since the air won’t cool the metal adjacent to it as well as the liquid would), the idea is to design the system so
the air will collect in a spot where it won’t do any harm so the owner can deal with it at his leisure.

In old pickup trucks, the top of the radiator was the highest point in the cooling system. As a result, any air in the
system would tend to collect right under the cap; all the owner had to do was top it up on occasion and the rest of the
circuit would remain air-free. Unfortunately, when Jaguar designed the XJ-S, the hoodline of a 1950 Ford pickup was
not considered acceptable; not only would the top of the radiator have to be so low that it would not be the highest point
in the system, but it wouldn’t have a cap on it either. Hence, more elaborate measures were necessary to continuously
purge air out of the system.

These measures changed with the introduction of a second radiator cap on the bypass pipe with the introduction of the
H.E. Mike Morrin says, “The Pre-H.E. XJ-S has only the cap on the header tank. The level of the cap is marginally
below the radiator vent valve (with the car on level ground).” There was a small tube from the top right corner of the
radiator over into the top of the header tank on the left wheel well. The bottom of the header tank was connected into
the return line from the heater line, which is essentially the suction side of the pump. The pump operation would
therefore draw a flow from the top of the radiator into the header tank. Within the header tank, the air would tend to
rise out and collect under the radiator cap while liquid coolant went out the bottom back into the circuit. The owner
simply tops up the system every now and then to keep air out.

With the H.E., it was decided to add a second fill cap on the bypass pipe. This formed another high spot where air
would collect. So, the air purge tubing from the top of the radiator to the header tank was modified to include a hose
connection for a line from a tap just under this second cap. Unfortunately, this complicated matters; the bypass pipe is
connected to the suction side of the pump, so it’s at low pressure. So, the coolant and air is likely to flow into the fill
connection rather than out toward the header tank. To make the air purge system work right, connections to the header
tank were revised. Rather than simply relying upon the suction side of the pump to draw coolant, an ejector was
incorporated into the air purge tubing to provide even more suction so as to pull air out of the cap fitting on the bypass
pipe. To operate this ejector, a hose was provided from the left side thermostat housing (high pressure) and there’s a
special connection on the bypass pipe directly into the suction side of the pump to get the lowest pressure possible. The
high flow resulting is routed through the ejector to provide as much suction as possible. The connection to the heater
return line was eliminated; the heater line merely passes underneath the header tank on its way to the radiator outlet.

Correction: The ©1982 Supplement, page 26-1, Fig. 2 showing the cooling system schematically shows the ejector
(item 18) incorrectly; the line from the radiator and the line from the left side thermostat housing are interchanged.

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Simply look at the tubing on your car to see the correct scheme. The same schematic with the same error is included in
the Haynes manual, page 334, Fig. 13.6.

The XJ12 with carburetors has a second radiator cap on the bypass pipe, but lacks the ejector-based air purge scheme.
Its air purge scheme operates similarly to the pre-H.E. except that it’s connected to the coolant passages in the induction
housings rather than to the top of the radiator.

On the H.E., in addition to the ejector scheme, a “water valve” EAC4168 was installed in the air purge connection to
the bypass pipe. This is basically a check valve that allows air to flow out towards the header tank but won’t allow
coolant to flow from the top of the radiator into the bypass pipe. This water valve is built into the fitting on the bypass
pipe itself. This requires a 3/8” fitting at that end, and since the air purge tubing is 1/4”, Jaguar uses a special hose
that’s 1/4” on one end and 3/8” on the other. Of course, if you want to replace the hose, you can use a piece of 1/4”
hose, a piece of 3/8” hose, and an adapter. Tony Bryant says, “I've brazed a 3/8" fitting onto the bleed pipe to be able to
use "standard" 3/8" heater hose here.”

If your water valve is toast and you can’t find a replacement, you can use a generic in-hose check valve, but be sure that
the unit you select opens very easily since the ejector will not provide enough suction to overcome a heavy spring. Bob
Lovell points out that McMaster-Carr (

http://www.mcmaster.com/

) offers a wide selection of check valves; the best

choice would probably be number 47245K23. However, better yet would probably be to make a check valve from
three successive sizes of brass tubing and a steel ball. Most commercially-available check valves consider a
positive closure of utmost importance, but in this case total cutoff is not as important as ease of opening. Don’t
install a spring in your assembly, just let the ball roll back and forth, and install it nearly horizontally.

If the air purge system doesn’t seem to be keeping air out of the space under the cap on the bypass pipe, it may be a
sign that the radiator is plugged. A plugged radiator will cause the pressure at the top right side of the radiator to be
higher than it should be. As a result, coolant will be coming out the banjo fitting faster than it should, possibly
overwhelming the air purge ejector and preventing any purge from the bypass pipe connection.

In either the pre-H.E. or H.E., the air purge system is attached to the radiator at a banjo fitting at the top right. This
banjo fitting has a design defect in that the hole through the side of the bolt itself is too close to the head, so it doesn’t
line up with the annular groove in the fitting properly. This exact same flaw is found in the banjo bolts on the back end
of the tappet blocks and is discussed at length beginning on page 43; the same modification should be done here to
improve flow, reduce the tendency to get plugged up, and make sure the air purge system works as intended. The banjo
fitting on the radiator is longer and has finer threads than those on the tappet blocks, but it is the same diameter.

If you don’t want to modify that banjo bolt yourself, Ron Kelnhofer (page 716) offers a replacement banjo bolt of his
own design. It is made of brass rather than steel, and it has the cross hole correctly located when used with the included
copper washers. You can look at a pic of this bolt at

http://neptune.spacebears.com/cars/engr/banjorad.html

While the defective banjo bolts on the oil lines don’t seem to cause obvious problems, this one tends to get plugged up
and completely shut off the air purge system from the radiator. David M. Johnson says, “After Kirby's info on the
banjo bolt being blocked, I took note and disassembled the bolt this weekend. Guess what, the holes in the bolt were
blocked with crud. One of my cars was making a disgusting moaning sound for the first minute after start up; the
moaning sound (trapped air) is now gone. Thanks Kirby, I would not have found that on my own.”

Craig Tims had more serious problems. After having the radiator rodded and the thermostats replaced at the dealer, the
car continued to overheat. He eventually found that the new thermostats had no jiggle pins and the banjo fitting was
totally plugged. After clearing and modifying the banjo fitting and correcting the thermostats, his temp gauge stays
where it should be. While such details may sound minor, Tims’ example should illustrate just how important it is to
have a working air purge system to keep air out of the coolant circuit.

Using thick sealing washers under the head makes the hole misalignment worse, so Jaguar provides really thin washers
that tend to leak. Once the modification to the bolt is done, the thick copper washers commonly found in auto parts
stores can be used for better sealing. This banjo fitting requires three seals, and the plug at the top left for venting the
radiator when changing coolant requires one more of the same size. If your local auto parts store has a rack of red cards

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titled “Help!”, it probably has a package of sealing washers that are perfect for these fittings: part number 66272,
labelled “Brake Hose Bolt Washer”. It says they are ID 25/64” and OD 5/8”.

Depending on personal preference, you might consider fiber washers instead of copper. This might be especially
advantageous on the plug at the top left of the radiator, since you may be opening that one more often and fiber washers
can be reused if care is taken while copper washers must be replaced (or annealed) each time to seal properly. 3/8”
fiber washers may be difficult to find in an auto parts store even though they carry lots of larger ones for oil drain plugs.
Lowe’s carries suitable fiber washers in its specialty fasteners section, part number 838050.

LEAK SEALERS: Mike Wilson says, “Here is what my 1990 XJ-S Drivers Handbook (publication number: JJM 18
02 03/00) states on page 176: “Two 135 ml bottles of Jaguar Radiator Leak Sealer or Barrs Leaks must also be mixed
with fresh anti-freeze”.

Folks, this horrible recommendation is probably the single biggest reason Jaguar didn’t make it on its own and had to
sell out to Ford. Many Jaguar mechanics owe their livelihood to this terrible advice, since a high percentage of their
work is traced to this stuff plugging up the bottom half of the radiator and contributing to Jaguar’s reputation for
overheating problems. Please, do not use any leak-sealing substance within the V12 cooling system. If the system
leaks, fix it.

To make sure no Barrs Leaks gets in there, you’re gonna have to keep the car’s cooling system away from Jag dealers.
Craig Sawyers reports: “Here's a horrible thing. I bought Jag antifreeze, determined I wasn't going to run the risk of
damaging my glitzy re-built V12 with the wrong stuff. Anyway, my dealer casually tossed in a Jaguar box marked
"2xJLM 636". "What is this?" say I. "Oh - corrosion inhibitor". That sounds good I think, particularly given the recent
thread on water types for radiator use, and electrolytic corrosion. Well, guess what is in the box? Two nicely packed
bottles of (unmarked) Barrs Leaks. AAARGH! Will they never learn! Needless to say, they are still in the box, and
will never even have sight of my rebuilt rad.”

If the car is more than a few years old and having overheating problems, it’s not a bad idea to just take the radiator to a
shop and have it rodded to restore its effectiveness -- especially if you’re not the original owner and the previous owner
may have been using leak sealers. John Napoli reminds you to clean out “the engine block, heater core and don’t
forget to remove and flush the expansion tank -- these are commonly forgotten repositories of Barrs Leaks.”

OTHER THINGS PLUGGING YOUR RADIATOR: Another major source of particles for plugging the tubes in the
radiator is rust scale, which primarily comes from four items in the XJ-S cooling system: the header tank, the cross
pipe, and a coolant connecting pipe on top of each head. Replacing some or all of these items with non-steel substitutes
would reduce or eliminate this source of crud. See pages 203, 207, and 211.

GURGLE SOUNDS: Paul Burke says, “I had a gurgle which was coming from around the heater matrix. It started
fairly quietly and only became audible when the car was stopped. I thought it was probably the air-conditioning system
- ha. The sound became loader over time and more apparent under acceleration. The noise turned out to be virtually
(well maybe not all, but more than normal) the full pump output going through the right hand bank of the engine, out
the back, through the heater matrix, along the hose that runs along the left hand side of the engine, into the small "T"
into the bottom hose and back to the pump thereby effectively bypassing the left hand side of the engine and the
radiator. My radiator had become partially blocked...”

FIXING A PLUGGED RADIATOR: Once you come to the realization that your radiator is plugged, there are
generally five things you can opt to do about it. The first is to go down to the store and buy some product intended for
“flushing” cooling systems and use it according to the directions. A quick survey of owners on the internet indicated
that this never does any good. Paul Bachman says, “I was told by a good source (must have been good 'cause I can't
remember who it was) that since the advent of aluminum engines and aluminum radiators there are no longer any
radiator flushing products that do anything useful at all. It seems the chemicals that used to do a fairly good job of

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cleaning out a brass/copper radiator cause serious corrosion to aluminum. Soo... rather than face complaints (lawsuits?)
from people who don't read directions, all such useful products just quietly disappeared from the shelves about 15 years
ago. I believe he went on to state that the antifreeze additives that were capable of keeping a brass/copper radiator free
from blockage were deleted at about the same time. thus the reason why most of our radiators are blocked or
becoming blocked. From my experience (from before 15 years ago), I have to say that this theory seems to have merit.”

Unfortunately, the next four options all involve removing the radiator. Deal with it.

The second option is to have the radiator “boiled”. This involves dunking the radiator in some kind of vat full of
chemicals and cooking it for a while. Again, a survey of owners indicates that this only rarely works with the XJ-S
radiator, possibly because of the types of junk that typically plug it. Considering how much effort it was to get it out
and put it back in, you might want to rethink this option.

The third option is to have the radiator “rodded”. In this case, the radiator shop removes the covers on each end of the
radiator and rams a rod through each tube from end to end, cleaning all the accumulated deposits out. He then solders
the covers back on and pressure checks the assembly. This usually does the trick, although there have been a few
reports when it didn’t; it may depend on how skilled your local radiator shop is. Jim Isbell says, “Some shops don't
know that to properly clean it both tanks have to be removed. If they only do one and you don't see any improvement it
just might be because it wasn't cleaned properly.”

Keep in mind that rodding does not render your radiator as good as new; the passages are unplugged but not all deposits
can be cleaned away, and some parts may be stressed or weakened during the procedure. Sometimes the shop will even
report that the radiator is toast and cannot be rodded, and suggest option number four.

The fourth option is to have the radiator “recored”, which means they take the end covers off and solder them onto a
new center section entirely. Apparently all brass radiators are made of comparable configuration cores, so the shop will
be able to find a suitable core. You need to ensure the new core is at least as good -- and possibly better -- than the
original was. Any upgrade generally involves the number of “rows” the core has. There is also a difference in fin
spacing, but if given a choice you should probably opt for the bigger fin spacing; the amount of cooling capacity is a
secondary concern compared to the likelihood of the fins getting plugged with debris, and it’s difficult enough to hose
out the radiator on this car.

The fifth option, of course, is to have the radiator replaced. You can opt for an OEM radiator -- but in this author’s
opinion, you’d be nuts to do so. As long as you’re buying a radiator anyway, take the opportunity to convert to a
single-pass arrangement as described on page 199.

If you’re doing any of this work on your radiator, you should be installing coolant filters to make sure that it doesn’t get
plugged again -- probably within seconds of starting, as all the crud sitting in your block is promptly flushed into your
freshly-cleaned radiator. Also consider the other items on the checklist on page 197.

COOLANT FILTERS: Everybody who has taken their XJ-S radiator to a shop and had it rodded out has been told that
it was really plugged up. The Jaguar recommendation to use Barrs Leaks in this system is often blamed, but there are
apparently other contributors as well. Rust scale coming off the inside of the header tank and cross pipe is a source of
crud. Some mechanics use too much silicone sealant so it leaves a bead around the joint, and later on this bead peels
off and starts looking for a passage to plug. And those who replace their coolant often but mix it with hard tap water
are introducing a whole new supply of minerals with each change; when the engine heats up, all these minerals deposit
on hot engine parts as a scale, and then break off in chunks and reconvene in the radiator.

Why don’t they make a “last chance” filter to install in the upper radiator hose to catch all this junk before it can get
into the radiator and plug things up? There are no small passages in the engine, the chunks could just flow right
through the block, but catching them before the radiator should greatly extend the time between roddings.

They do. In fact, it’s a fairly popular idea among car enthusiasts, so there are several different model filters available.
Brian Schultetus provided one source: