Jaguar XJ-S. Service manual — part 15

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to prevent wear, but gets hot enough to melt the soft bearing material because the same oil is staying in there and
getting hotter and hotter, rather than cool oil flowing through.

All engines tend to display a drop in oil pressure at idle; the pump moves less oil when the engine is turning slower, but
the openings through which the oil flows are the same size no matter what the engine speed. The Jaguar V12 is no
exception, and sometimes shows lower oil pressure when hot and idling, especially when it has a few miles on it. The
V12, when running on all cylinders, can idle very slowly, causing even lower pressure. This causes many XJ-S owners
to panic, and some to take poorly conceived countermeasures.

There is no magic value for oil pressure. The only real need for any pressure at all is to get oil to all points in the
engine, and this would only require a couple psi. Oil pressure is monitored simply to insure there is oil flow, which is
essential.

If your car has always had low pressure at idle when hot, and it gradually over the years gets a little lower, don’t worry
about it. If it suddenly has much lower pressure than it used to, you may have a damaged bearing that is allowing oil to
flow through too fast; the cause should be investigated. If your car suddenly has no oil pressure at all, stop
immediately, do not drive it one more minute until the problem is located and corrected. Many motorists fail to
understand the importance of this, so I will emphasize: If the red light on the dash comes on indicating that you have
no oil pressure, it is not good enough to “take the next exit.” You should pull over immediately, possibly even shutting
the engine off while still moving. A towing fee, and even an illegal parking ticket, is a minor expense compared to an
engine replacement, which is the inevitable result of driving with no oil pressure.

Do not add oil thickeners to your oil. While these may increase the indicated oil pressure at idle when hot, they do no
real good and can do considerable harm. In particular, when cold the oil may be so thick that very little flows and most
of the output of the oil pump is wastegated through the pressure relief valve. While there is good pressure, there is little
flow to the bearings, and they may fail due to lack of cooling flow before the engine and the oil warm up. This is also a
good reason not to run the engine too hard until it is fully warmed up.

OIL PRESSURE SENDER: The oil pressure sender on the pre-’92 XJ-S is notorious for leaking; see page 46. It’s also
fairly well known for electrical maladies. Tom Mackie says, “My oil pressure sender is getting flaky. I connected an
ohmmeter and found that rather than nice varying resistance readings, it sometimes goes open. Which makes me
wonder how accurate this particular unit has been all along.”

If the connector on top is loose, Mike Morrin provides some insight: “The connector moving around is due to some
little plastic pegs broken inside, and will cause the sender to read low. You can uncrimp the top and get inside to glue it
down.” Since uncrimping is difficult, others suggest cutting right through the circumference of the can to get the top
off, fixing the innards, and putting the top back on with aluminum tape or JB Weld or some other mechanical means.

Ed Sowell provides electrical data to aid diagnosics: “Here are the measurements from my sender and gauge, for what
it's worth:

Oil pressure sender (markings: PTR 1001/10/EC 700kn/m

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, 29-7 Part #46272):

Engine off: 350 ohms

Cold engine idle: 80 ohms ( I believe the oil pressure is about 60-70 psig under these conditions)

Oil pressure gauge:

290+ ohms = 0 psig

55 ohms = 50 psig

10 ohms = 100 psig

short to ground = off top of scale.”

I’d like to be able to tell you what commonly available sending unit can be used for a substitute, but I can’t; nobody’s
worked one out yet. The pre-’92 Jaguar V12 uses a 0-100 psi oil pressure gauge while Jaguar 6-cylinder cars use a 0-
80 psi gauge, so senders from other Jags won’t work. Before trying a sender from any other car, make sure it has the 0-
100 psi range. Electrical oil pressure gauges with 0-100 psi ranges are very common as aftermarket items, though, so
perhaps the sender from one of those will work. Summit (page 717) and Jeg’s (page 714) offer many such gauges, or

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you can probably find a fair selection in a local auto parts store or speed shop. Unfortunately, the senders are often
included with the gauge itself rather than sold separately, but you still might get off cheaper than buying the Jag part
even throwing the gauge away.

There are two issues that must be addressed to get an aftermarket sender to work. The first is physically installing it.
The threads on the bottom of the OEM sender are BSPP (see the section on the radiator drain plug on page 194), while
the generic senders typically have 1/8” NPT fittings. You could buy a BSPP fitting and plumb a line to a remotely-
mounted sender -- or just opt to replace the entire pedestal. It’s possible the pedestal from the ‘92-on cars would work,
or you could actually just make one from a block of aluminum. If you don’t mind how it looks, you can simply plug
the hole in the original pedestal by cutting off the bottom of the OEM sender, putting a bolt through the center, and
screwing it back into the hole, and then tee off the fitting for the oil pressure switch (standard 1/8” NPT) to connect up
a sender with NPT threads.

The second concern is finding a sender with the correct pressure vs. ohmage response. Unfortunately, neither Summit
nor Jeg’s provide such data; if you can’t find such specs or talk a local shop into letting you check one out with a tire
pump and a VOM, you may just have to take the risk and buy one to see what their electrical characteristics are.

For now, your best option may be to shop around the mail order places for the OEM part, since prices on this item seem
to vary widely and it sometimes can be found for a quite reasonable cost.

If you have the ‘92-on with round gauges, you are in worse trouble. Read about steady oil pressure below.

REPLACING THE OIL PRESSURE SENDER: Julian Mullaney says, “Use a crow's foot and several thin extensions.
It is a superb test of dexterity and patience, but I did it. To install the new one, I attached it to a coat hanger and started
the thread that way.”

Stefan Schulz says, “Have you tried a plumber's tool called a basin wrench ? GBP5 at the nearest DIY store.”

Craig Sawyers says, “What I did was undo the banjo bolt that links the camshaft oil feeds to the back of the alloy
pedestal that holds the oil pressure sender. Then I undid the two 7/16" af bolts that hold the pedestal down and took the
pedestal plus oil pressure sender out as a unit. Changed the sender, and reversed (as they say) the removal procedure.
Made it all very easy, when originally it looked damned near impossible. The Jag ROM and Haynes were less than
useless.”

REALLY STEADY OIL PRESSURE: Bill Letter reports: “Today the kitty went in for a number of "adjustments", the
most important of which was to determine why my oil pressure gauge always reads 58 psi at idle (hot or cold). On my
last visit to the same dealer for the same problem, I was told that the gauge was working fine and according to Jaguar
Spec. Today I was shown a TSB that explained that Jaguar changed the oil pressure senders on the XJ12 Sedan and
XJS V12 (in 1996) to a new type which is actually not a sender at all. It seems (according to the dealer) that numerous
customer complaints of their oil pressure gauge reading too low (less than 25 psi) when hot at idle caused Jaguar to
discontinue manufacturing the oil sender and instead replace it with an oil switch which acts like an idiot light (when
there is more than 7 psi pressure it will always read 'ON' or in my case 58 psi, when there is less than 7 psi oil pressure
it will read 'OFF' or zero psi). So it was explained to me that the updated oil switch was installed in my car last year.

“It is Jaguar TSB Number 15-13 dated 06/95 and covers all cars with V-12 engines and some AJ16 engines on the XJS
(MY '95 on). They removed the senders and installed a simple switch because of customer complaints that the needle
would read lower oil pressure when hot at idle!”

You may have difficulty trying to undo this “upgrade” since the real sender is officially NLA. Gregory Wells of
Coventry West, Inc. explains in detail: “The sender issue is confined to '88-on XJ40 cars and '92-on XJ-S with 4.0L,
5.3L, and 6.0L engines (VIN 179737 onwards). Jaguar has superceded all sender numbers (viz. DBC4418, DBC5513,
DAC7879, DAC11141, LMD5640AB) to JLM20791, which looks like the old C42200 (now superceded to
LHD5642AA) switch for the oil pressure light on the Series III cars. Included in the bag with the sender is a small
harness which seems to only have a resistor in it. If one orders any of the above five part numbers from Jaguar, a
JLM20791 will be supplied. I've checked the '88-92 XJ40 fiche, the '93-94 XJ40 fiche, the '87-91 XJ-S fiche, and the

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'92-on XJ-S fiche and they all show gauge sender part numbers that eventually supercede to the on/off sender p/n.”
However, if you’re persistent, you may be able to find a dealer or supplier that has some of the real senders in old stock.

Note that none of this seems to apply to the pre-’92 XJ-S.

There are two things to note regarding the ’92-on senders vs. the pre-’92 senders that may be relevant: First, the pre-
’92 sender (C46272) has BSPP threads and requires a sealing washer, while the ’92-on sender has the same tapered
pipe thread that the oil pressure switch has (1/8” NPT). Second, the oil pressure gauge on the pre-’92 dash is the
vertical indicator with a 0-100 psi range while the ’92-on dash has a round gauge with a 0-80 psi range. Together this
may mean that a standard Ford oil pressure sender might work in this car.

ENGINE WORK

ENGINE OVERHAULS: If you take your XJ-S to a disreputable dealer with major engine problems, they may tell you
that a fine machine like this cannot be rebuilt, and try to charge you $10,000 to put in a new engine. Of course, one of
the features that make this a fine engine is that it can be rebuilt. It is not a disposable engine; all wear items can be
replaced. Even the cylinder liners can be easily replaced, so there is no need for boring and honing or for oversize
pistons. Of course, if you’ve overheated the engine and warped the block, or you’ve had a major engine fire, you will
definitely need a new motor.

If the engine has to be rebuilt but you aren’t up to the task yourself, you may find it challenging to find a mechanic you
feel is competent to do the job. Fortunately, if you live in the US, there may be an alternative to taking your chances
with the local grease monkeys or a Jaguar dealer: Crow Engineering, 1-800-537-4146. This is a very interesting
business run by a British guy named Stewart Plant who apparently spends a few months each year in the US. By
appointment, he and an assistant will drive to your house and rebuild your engine in your garage. He arrives in a panel
van with all the tools and parts needed and will typically finish the task in a week or so. He and his assistant sleep in
the van; the only accommodation they ask from you is to use your shower. Their services are not cheap, but they’re
undoubtedly cheaper than paying a dealer for a new engine -- and you’re more likely to be told why your engine was
damaged and how to avoid it happening again.

Rebuilding by the home mechanic is not out of the question. It’s imposing at first; the engine compartment is crammed
quite full. But with this book, a repair manual of some sort, a good set of tools, and time and patience it can be done --
and the money saved will probably be enough to pay for that good set of tools! The biggest disadvantage of going this
route is usually the time involved; typically, a mechanic will disassemble the engine, figure out what parts he needs,
order the parts, and then wait, and wait, and wait for the parts to show up -- only to find out that a few of them are
incorrect and must be returned and reordered. And, of course, on reassembly he will figure out what he forgot to order.
As a result, even though only a week or two of actual labor may be involved, the car may be scattered all over the place
for a couple of months or more.

If you decide to tackle such a teardown, note that the V12 weighs something like 700 pounds as it is pulled from the
car. You don’t want to be working with flimsy hoists or engine stands; obtain the heavy-duty stuff, perhaps even items
intended for trucks.

ENGINE ASSEMBLY LUBE: When an engine is first started after assembly is when much of the wear occurs -- in
the several seconds it takes before oil pressure and flow to the bearings is established. To counter this problem, there is
a product called “Penrite Camshaft & Engine Assembly Lube”. This is made specifically for use on all plain bearings
(mains, big ends, etc.) as well as on cams, when assembling a rebuilt engine. It claims to withstand loadings “greater
than 200000 p.s.i.”, which is almost 100 tons per sq. inch. It is an Australian product, but equivalents may be available
in other countries.

Another idea is to simply fill the freshly-rebuilt engine with oil through the galleys instead of the filler cap, thereby
lubing all the bearings before it ever turns over. All you need is a pressure vessel capable of holding at least 3 or 4

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quarts with a tire valve at the top and a hose out the bottom with a selection of fittings that will thread onto the oil filter
fitting. After reassembly, you thread the thing onto the oil filter fitting, put new oil in the tank, close it up, and apply
compressed air to the tire valve. The pressure will blow the oil into the galleys and on into the bearings. After enough
oil has been blown in to establish steady oil flow through the system, the feed is cut off before the tank empties and
blows air into the galleys. Then install a new filter and add the rest of the oil necessary the normal way to establish the
proper level in the crankcase prior to startup.

Andrew Holley describes what he did with a motorcycle engine: “What I did was get hold of an old fire extinguisher,
the water/stored pressure type. Has about a 15 litre capacity; the handle has a tyre valve built into it with pressure
gauge as well. After draining and cleaning, filled it with oil and attached the hose via a suitable fitting to one of the oil
cooler lines. With about 60 psi of air in the tank, it forced the oil through all the passageways. Simple and effective.”

Tom Amlie: “Prelubing a rebuilt engine is sometimes difficult, but in this case it was easy. There is a pipe plug on the
little pedestal that holds the oil pressure sender and the idiot light switch. As best I could tell, it was 1/8 NPT. Got a
cheap ($13) plastic garden sprayer and cut the hose to match 1/8 pipe. Put 8 quarts through it. Worked great.”

You might want to use a good assembly lube and pre-oil the engine before startup. Blowing oil into the galleys will do
wonders for reducing wear in bearings and cam followers during that first startup, but you won’t get any oil on the
cylinder walls until the crankshaft is spinning. So having a good assembly lube on the cylinder walls is a good idea.

Engine Work -- Top

MANIFOLD CROSSOVER PIPE HOSES: On the author’s ’83, the intake manifold crossover pipe is connected to the
manifolds with a short, straight piece of 1” hose at each side. However, sometime before ’89, the assembly was
changed so that pieces of hose with 45º bends are required. A cursory look at the two assemblies leads one to believe
that the parts themselves are in fact unchanged, and the later cars were merely assembled with elbow hoses to relocate
the crossover pipe higher across the back of the engine. This might actually be helpful in making condensation drain
out of the crossover pipe back into the manifolds rather than into the vacuum line to the ECU, which really messes
things up.

If you have the earlier straight hoses and need to replace them, it’s obviously pretty easy to find pieces of 1” hose. As
for the later parts, Jeff Elmore says, “The dealer quoted me $22 apiece for these three inch long, 7/8-1" diam hoses with
a 45 degree bend in it. Bennett Auto Supply had a Goodyear coolant bypass hose that fit perfectly for $2.62 apiece.
Part number #gyy 63064.”

Whatever you fit, note that the vacuum inside these parts is considerable, and long unsupported sections of rubber hose
will be sucked flat. With the earlier design with straight hoses, it appears to be sufficient to merely be sure to insert the
hoses far enough onto the fittings that there is only a short area of hose that doesn’t have fittings within it. If you must
have longer sections, you may need to insert a piece of wire coiled like a spring to hold the hose round, or perhaps just
a short section of tubing.

RUNNING WITHOUT AIR FILTER HOUSINGS: Frank Perrick points out that if the engine is to be started without
the air filter housings bolted on, the bolts themselves must be screwed in. The bolts that hold the air filter back plate
onto the butterfly housings actually go all the way through the housings and are threaded into the intake manifold. If
these bolts are left out, the holes provide a major butterfly bypass and the engine will overrev.

CAM COVER WORK: If you need to get down to the cam covers or beyond, Victor Naumann sends this awesome
tip: Remove the PCV crossover manifold, fuel rail and injectors, air injection manifolds, both fuel pressure regulators,
the ignition amplifier, the intake manifold crossover pipe, both butterfly housings, and both intake manifolds as one
piece. Be sure to disconnect the butterfly return springs before lifting.