[xj] Cooling System Pressure

XJ
1

Hello Forum,

I was wondering about the pressure in the cooling system on
a Series 2 XJ6 4.2.
I have bought new radiator caps a few months ago. On the
thermostat housing I have a flat cap and on the expansion
tank I have a 15 pound cap. This is what SNG Barratt told me
to get and I bought it from them.
First of, is this correct?
Secondly, should I be able to feel a pressure on the top
hose when the engine is up to temperature? On other classic
cars I’ve had you can feel a pressure when its warm.
I have replaced all my hoses except the ones leading from
the thermostat housing to the expansion tank. I will do that
very soon. I noticed that one has a fold in it. Could this
cause me not feeling a pressure in the top hose, if I
should.
I don’t have any cooling problems and the car stays at the
correct temperature (middle of the gauge, thermostat
temperature)
I do notice that the level in the expansion tank changes
with temperature which I believe is correct. Also if I put
too much coolant in the system the expansion tank will expel
it through the overflow hose.
Any insight would be great. Maybe I’m just worrying about
nothing since the cooling has worked for me.

-Adam–
Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands
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2

In reply to a message from Adam XJ6 sent Fri 1 Jun 2012:

The advice Barratts gave is correct, the cap at the end of the
thermo housing should be a flat one.

Did you get all the air out of the system when filling? That
centre cap is helpful for this. So is having the car pointing up
hill when filling.

With the system completely cold, the coolant should be up to the
bottom of the neck of the centre cap. If it isn’t and there’s
coolant in the expansion tank, you’ve got an air leak somewhere.
What should happen is that as it warms, the coolant expands and
will flow into the expansion tank (so this needs to be less than
full when cold.) Once the system cools, it should suck back
coolant from the expansion tank, so the engine is always full, but
the expansion tank is only part filled.

By the sound of it, your system is working as intended. If you
want to go to even greater levels of reassurance, buy, beg, borrow
or steal an infra red digital thermometer (electrical parts houses
sometimes have them at a discount - mine cost �14) and take
readings on the water components, intake manifold, hoses &c. You
will most likely get readings in the 80�C - 90�C range.

Not sure if you would feel 15 psi pressure through a Jaguar top
hose. All the ones I’ve encountered seem rather more robust than
that, maybe someone else will chime in?–
The original message included these comments:

thermostat housing I have a flat cap and on the expansion
tank I have a 15 pound cap. This is what SNG Barratt told me
First of, is this correct?
Any insight would be great. Maybe I’m just worrying about

–
al mclean '05 X 2.0 D Estate- '93 XJS 4.0 - 05 X350 2.7TDVi
Telford, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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3

Adam XJ6 wrote:

Hello Forum,

I was wondering about the pressure in the cooling system on
a Series 2 XJ6 4.2.
I have bought new radiator caps a few months ago. On the
thermostat housing I have a flat cap and on the expansion
tank I have a 15 pound cap. This is what SNG Barratt told me
to get and I bought it from them.
First of, is this correct?
Secondly, should I be able to feel a pressure on the top
hose when the engine is up to temperature?

That depends on the hose, Adam - but most hoses will feel ‘softer’ when
unpressurized…

As Al says, all correct and basically nothing really to worry about. Any
leaks will depressurize the system - best verified by regularely
checking expansion tank with the engine cold; any gradual drop in level
will then indicate a leak. One can also check for leaks with pressure
test equipent, but there is no ‘safe’ way of verifying that there is
pressure with the engine hot - opening the cap with a hot engine is a
bit iffy…

As Al also says; an infrared thermometer is a valid investment - though
there are no indications you have a problem…time may come. But at
present you indeed seem to be ‘worrying about nothing’…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)>On other classic

cars I’ve had you can feel a pressure when its warm.
I have replaced all my hoses except the ones leading from
the thermostat housing to the expansion tank. I will do that
very soon. I noticed that one has a fold in it. Could this
cause me not feeling a pressure in the top hose, if I
should.
I don’t have any cooling problems and the car stays at the
correct temperature (middle of the gauge, thermostat
temperature)
I do notice that the level in the expansion tank changes
with temperature which I believe is correct. Also if I put
too much coolant in the system the expansion tank will expel
it through the overflow hose.
Any insight would be great. Maybe I’m just worrying about
nothing since the cooling has worked for me.

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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4

In reply to a message from Frank Andersen sent Fri 1 Jun 2012:

Thanks Al and Frank!
I was hoping I would get this answer that all seems well.
I’m preparing for a long road trip in a few weeks since i’m
moving back home after many years abroad and of couse i’m
taking the XJ with me. Since its a 1,000 km (621 miles) I’m
double checking everything on the car before I set off.
I’m planning of starting a topic later with preparing 30
year old cars for a long drive. I’m starting to think that I
have a better check and knowledge of all the parts on my old
XJ compared to many friends 2 or 3 year old cars. Maybe its
an obsessive hobby but I wouldn’t want serious to go wrong
on the trip.
An infrared thermometer is on my wish list of tools but I
did use a high temperature thermometer last year which I
built into an old radiator cap and it confirmed that when
the needle is in the middle of the ‘‘normal’’ part of the
scale, the coolant is between 82 and 84 degrees Celsius.
Which corresponds to my thermostat.

-Adam–
The original message included these comments:

That depends on the hose, Adam - but most hoses will feel ‘softer’ when
unpressurized…
As Al says, all correct and basically nothing really to worry about. Any
leaks will depressurize the system - best verified by regularely
checking expansion tank with the engine cold; any gradual drop in level
will then indicate a leak. One can also check for leaks with pressure
test equipent, but there is no ‘safe’ way of verifying that there is
pressure with the engine hot - opening the cap with a hot engine is a
bit iffy…
As Al also says; an infrared thermometer is a valid investment - though
there are no indications you have a problem…time may come. But at

–
Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
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5

Adam XJ6 wrote:

In reply to a message from Frank Andersen sent Fri 1 Jun 2012:

Thanks Al and Frank!
I was hoping I would get this answer that all seems well.
I’m preparing for a long road trip in a few weeks since i’m
moving back home after many years abroad and of couse i’m
taking the XJ with me. Since its a 1,000 km (621 miles) I’m
double checking everything on the car before I set off.
I’m planning of starting a topic later with preparing 30
year old cars for a long drive. I’m starting to think that I
have a better check and knowledge of all the parts on my old
XJ compared to many friends 2 or 3 year old cars. Maybe its
an obsessive hobby but I wouldn’t want serious to go wrong
on the trip.

Any odds that the only stops you will need is comfort and petrol, Adam…:slight_smile:

System temp reading vary with the place measurements are taken - the
dash gauge reads from the temp transmitter on the water rail. Measures
taken elsewhere may vary; the expansion tank takes little part in
coolant circulation and will likely be low. At the radiator; the top
hose will nominally show thermostat temps when the 'stat is fully open -
but coolant temp will quickly drop when out of the engine, or the
thermostat closes…

The infrared thermometer can be moved around to read at various places,
which is a useful diagnostic process in some cases. But the ‘true’ temp
of the engine is at the water rail, other reading points may be used for
diagnostic purposes…

And incidentally; loss of pressure does not in itself affect engine
cooling…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)>An infrared thermometer is on my wish list of tools but I

did use a high temperature thermometer last year which I
built into an old radiator cap and it confirmed that when
the needle is in the middle of the ‘‘normal’’ part of the
scale, the coolant is between 82 and 84 degrees Celsius.
Which corresponds to my thermostat.

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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6

In reply to a message from Frank Andersen sent Sat 2 Jun 2012:

I’m quite confident my cooling is fine but I will double check
with a thermometer when I can borrow one.
I think those will be only stops, mostly for petrol as my
‘‘new’’ VDP seats are incredibly confortable. It feels like you
could just for hundreds of miles and feel great.
I plan on taking pictures along the way, which I will post,
since i’m driving with my father who is taking is '91 XJS V12 Convertible Classic Collection. Its going to be a high octane
fueled trip in two old cats:)

-Adam–
The original message included these comments:

Any odds that the only stops you will need is comfort and petrol, Adam…:slight_smile:
System temp reading vary with the place measurements are taken - the
dash gauge reads from the temp transmitter on the water rail. Measures
taken elsewhere may vary; the expansion tank takes little part in
coolant circulation and will likely be low. At the radiator; the top
hose will nominally show thermostat temps when the 'stat is fully open -
but coolant temp will quickly drop when out of the engine, or the
thermostat closes…
The infrared thermometer can be moved around to read at various places,
which is a useful diagnostic process in some cases. But the ‘true’ temp
of the engine is at the water rail, other reading points may be used for

–
Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

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7

Adam,

as Frank said, there is no need to be obsessive, if you had a chance to
observe the car over a certain period of time - and did so! If it runs
and drives fine for one hour give city take motorway, it will do the
same thing for many hours. These cars were designed to cover large
distances. Your cat will feel a lot better with one 1000 km-trip than
with 1000 1 km rides to the letter box.

The stock XK engine design is probably not fully WOT proof, but it’ll
stand at least many minutes of full speed without anything discomforting
but the rapid decline of the fuel needle - I tested this;-). At anything
up to 140-160 kph the car can go for ages.

If you want to cross the Death Valley, double-checking the cooling makes
perfect sense, likewise if you have mountain ranges to cross, but had
the car only in city traffic so far, I’d go over the brakes as well. You
might wish to check the age of the brake fluid and change, if necessary.

For the trip take a full tool set, the ROM, duct tape, two coat hangers
with pliers and a full assortment of fuses with you. If you’re really
paranoid add a dizzy cap and a set of coolant hoses. Nothing will happen
then!

Ah …, don’t forget AAA (or equivalent) membership card, cellphone and
a laptop computer :slight_smile:

Good luck and keep us posted from your trip - are you going south from
the NL?

Jochen

75 XJ6L 4.2 auto (UK spec) - did the first trip over 400 km autobahn @
approx. 140 kph with four-year-old son on baby seatDate: Sat, 2 Jun 2012 16:08:30 -0700

From: "Adam XJ6"speedyswed@hotmail.com
Subject: Re: [xj] Cooling System Pressure

In reply to a message from Frank Andersen sent Fri 1 Jun 2012:

Thanks Al and Frank!
I was hoping I would get this answer that all seems well.
I’m preparing for a long road trip in a few weeks since i’m
moving back home after many years abroad and of couse i’m
taking the XJ with me. Since its a 1,000 km (621 miles) I’m
double checking everything on the car before I set off.
I’m planning of starting a topic later with preparing 30
year old cars for a long drive. I’m starting to think that I
have a better check and knowledge of all the parts on my old
XJ compared to many friends 2 or 3 year old cars. Maybe its
an obsessive hobby but I wouldn’t want serious to go wrong
on the trip.
An infrared thermometer is on my wish list of tools but I
did use a high temperature thermometer last year which I
built into an old radiator cap and it confirmed that when
the needle is in the middle of the ‘‘normal’’ part of the
scale, the coolant is between 82 and 84 degrees Celsius.
Which corresponds to my thermostat.

  • -Adam

The original message included these comments:

That depends on the hose, Adam - but most hoses will feel ‘softer’ when
unpressurized…
As Al says, all correct and basically nothing really to worry about. Any
leaks will depressurize the system - best verified by regularely
checking expansion tank with the engine cold; any gradual drop in level
will then indicate a leak. One can also check for leaks with pressure
test equipent, but there is no ‘safe’ way of verifying that there is
pressure with the engine hot - opening the cap with a hot engine is a
bit iffy…
As Al also says; an infrared thermometer is a valid investment - though
there are no indications you have a problem…time may come. But at

Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

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8

In reply to a message from =?ISO-8859-15?Q?Jochen_Gl=F6ckner? sent Sun 3 Jun 2012:

Hey Jochen,

Sorry for the late reply, I just got back from my new place
and it doesn’t have internet yet.
Today I finished of most of the things on the car and took
her for a longer test drive and she did very well. No
complaints after and hour on the highway at about 120km/h.
I’m beginning to look forward to the longer trip next week
since she seems to be very comfortable highway cruiser.
I will actually be going North from NL to Sweden. Its where
i’m originally from but I’ve hardly ever lived there.
What i’m most excited about is that now I will finally have
a garage for the Jag thats next to where I live. And due to
the harsh climate in Sweden she will only be out during the
spring and summer when its nice out. Otherwise I will
continue to renovate her during winter months.
Since I see that you have a series 2 XJ6 also, is it normal
to the ‘‘suction’’ from the SU’s from the passenger
compartment?–
The original message included these comments:

Adam,
as Frank said, there is no need to be obsessive, if you had a chance to
observe the car over a certain period of time - and did so! If it runs
and drives fine for one hour give city take motorway, it will do the
same thing for many hours. These cars were designed to cover large
distances. Your cat will feel a lot better with one 1000 km-trip than
with 1000 1 km rides to the letter box.
The stock XK engine design is probably not fully WOT proof, but it’ll
stand at least many minutes of full speed without anything discomforting
but the rapid decline of the fuel needle - I tested this;-). At anything
up to 140-160 kph the car can go for ages.

–
Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

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9

Adam,

I’m not entirely sure I understand your question. Besides I can’t
compare the car to non-carbed species, as I’ve only driven SI and SII
cars so far. In both types the engine appears very remote, quiet and
smooth, as expected from a luxury sedan. The auto species kind of
muffles everything in the permanent howl/whine of the gearbox. Even
driven to 5000 RPM the engine will keep its countenance and there is
neither intake nor exhaust sound taking over, at least from the driver’s
seat. I’m running the standard air filter box on the SUs. When you tune
the engine and pull the accelerator cable in N with the front hood open
and your head in the engine bay the inline six sounds quite impressive
though.

Why don’t you take the chance to go from NL through D, CH, I, A and CZ
to DK? Would add some 2000 kms, but also a lot of fun! Last week I used
the XJ for two business trips through the Swiss countryside with narrow
winding roads. First night I returned well after midnight through heavy
rain; second day I started early in the morning in - guess what - heavy
rain, but the beast (a PO used to call her “Gussy”) didn’t miss a beat
and took me home and back in comfort, with demisted windows and perfect
cabin temperature. The balance of the car on the wet roads was just
awesome and pretty close to anything 20 years younger and on lower
profile tires. BTW, my new cheapo tires are just wonderful.

Good luck at any rate - SE is a great place for classic cars!

Jochen

75 XJ6L 4.2 auto (UK spec)Date: Sat, 9 Jun 2012 09:26:55 -0700

From: "Adam XJ6"speedyswed@hotmail.com
Subject: Re: [xj] Cooling System Pressure

In reply to a message from =?ISO-8859-15?Q?Jochen_Gl=F6ckner? sent Sun 3 Jun 2012:

Hey Jochen,

Since I see that you have a series 2 XJ6 also, is it normal
to the ‘‘suction’’ from the SU’s from the passenger
compartment?

Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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10

In reply to a message from =?ISO-8859-15?Q?Jochen_Gl=F6ckner? sent Sun 10 Jun 2012:

Hey Jochen,
I just meant a slight sucking sound when you begin to
accelerate. I think it just normal. This is the only car
i’ve driven with SU carbs. Everything is standard on the
car. I believe I might have a slight exhaust leak from where
the headers connect to the downpipe, that might be what i’m
hearing. I will fix that and see what happens.
I would love to take a longer trip with the XJ but i’m on a schedule and i’m having a friend drive next to me in a
modern station wagon that has the last of my things going to
my new home.
I plan on driving up north in Holland past the lake, into
germany and then take the brides in Denmark and finally that
one that connects Denmark to Sweden. My destination is only
30 minutes from that bridge.
About tires I could use a new set when I have some extra
cash. They still have tread on them but they are all season
tires that are a little bit noisy on the highway. I’m saving
to get the period correct tires with the thin white strip.
Maybe this winter I can buy them for the car for Christmas.

-Adam–
The original message included these comments:

Adam,
I’m not entirely sure I understand your question. Besides I can’t
compare the car to non-carbed species, as I’ve only driven SI and SII
cars so far. In both types the engine appears very remote, quiet and
smooth, as expected from a luxury sedan. The auto species kind of
muffles everything in the permanent howl/whine of the gearbox. Even
driven to 5000 RPM the engine will keep its countenance and there is
neither intake nor exhaust sound taking over, at least from the driver’s
seat. I’m running the standard air filter box on the SUs. When you tune
the engine and pull the accelerator cable in N with the front hood open
and your head in the engine bay the inline six sounds quite impressive

–
Jaguar XJ6 4.2 Series 2 Jessie
Den Haag, Netherlands
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

To remove yourself from this list, go to http://www.jag-lovers.org/cgi-bin/majordomo.

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