I have been letting my brother drive Harlem since she
arrived here after my purchase. He reports that she seems
to have a persistent coolant leak, with the ‘‘low level’’
light coming on approximately weekly, requiring a top up.
There’s no sign of leakage underneath the car. He reports
there is a strong smell of coolant though around the engine
compartment area (never in the cabin) but he doesn’t see any
wet spots.
Any ideas on this issue?–
& Paul '94 XJS 4.0 cp. (
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
I have been letting my brother drive Harlem since she
arrived here after my purchase. He reports that she seems
to have a persistent coolant leak, with the ‘‘low level’’
light coming on approximately weekly, requiring a top up.
There’s no sign of leakage underneath the car. He reports
there is a strong smell of coolant though around the engine
compartment area (never in the cabin) but he doesn’t see any
wet spots.
In reply to a message from Jerry Jones sent Fri 1 Apr 2016:
I had the same problem on my 2002 XJ8; a slow disappearance
of coolant and a need to top up every couple of weeks, but
no obvious source. Then, while on a road trip, the engine
suddenly overheated and I had to be towed to a repair shop.
It turned out to be the thermostat housing, which was made
of plastic, had developed a hair line crack which allowed
coolant to be slowly lost and boiled off by engine heat as
it seeped out. The replacement housing is made of metal (as
it should have been in the first place) and I’ve had no
further problems with loss of coolant.–
Mark 1E14988 67 OTS, 2002 VDP
Burke, VA, United States
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In reply to a message from mgordon sent Sat 2 Apr 2016:
Ah, so that’s what the rub is with the thermostat housings
on the XJ8s. I wondered why advice was given earlier on
here to check and replace it with an ‘‘upgraded’’ version. It
is metal. I don’t understand why Jag apparently decided to
‘‘cheap out’’ and go with a few plastic parts instead of
metal, beginning with the XJ8s (namely that housing and the
timing chain tensioners). GRRRR.
Well, I asked my brother about that, and he said the
coolant smell was not in the vicinity of the thermo cover
(i.e. the front area of the engine compartment) but toward
the rear of the compartment. Does that sound more in line
with the leaky hose down in the ‘‘V’’, mentioned earlier?
btw, I don’t see any way to check that area of the engine
w/o pulling stuff off the top of it … or can it be
inspected easily if the car is on a lift?–
The original message included these comments:
It turned out to be the thermostat housing, which was made
of plastic, had developed a hair line crack which allowed
coolant to be slowly lost and boiled off by engine heat as
it seeped out. The replacement housing is made of metal (as
it should have been in the first place) and I’ve had no
further problems with loss of coolant.
In reply to a message from AttyDallas sent Sat 2 Apr 2016:
If it’s a V8 the coolant /heater hoses tha pass under the inlet
manifold are a likely place to look. With the gnine fully hot and a
full, pressurised coolant system you might just get lucky and spot
it. Cold, stiff hoses don’t leak anywhere near as well as hot,
flexible ones!
In reply to a message from Jags on gas sent Sun 3 Apr 2016:
You should also check the teo hoses on the coolant expansion
tanlk to be sure they are not installed backwards. They
appear to cross when connected properly, the top hose of the
two going into the wheelell and the lower one going to the
radiator.–
Ross - 89 XJS, 99 XJR, 02 XJ8, 12 XF-R
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In reply to a message from sparkenzap sent Sun 3 Apr 2016:
k. I had wondered if the XJ8s had the usual ‘‘coolant
overflow tank concealed in the wheel well’’ thing with prior
models. Thanks guys.–
The original message included these comments:
You should also check the teo hoses on the coolant expansion
tanlk to be sure they are not installed backwards. They
appear to cross when connected properly, the top hose of the
two going into the wheelell and the lower one going to the
radiator.
In reply to a message from sparkenzap sent Sun 3 Apr 2016:
Ross,
For some reason I completely forgot to add that - I was in a bit of
a rush. Good job there’s more than one of us and thanks for the
nudge!
The Header Tank tube potential mix-up could certainly be the cause
and is described with pictures someway down this page;
Regards
Steve–
The original message included these comments:
You should also check the teo hoses on the coolant expansion
tanlk to be sure they are not installed backwards. They
appear to cross when connected properly, the top hose of the
two going into the wheelell and the lower one going to the
radiator.
In reply to a message from AttyDallas sent Sat 2 Apr 2016:
Jag decided to ‘cheap out’ for the same reasons every
other maker has done, with engine and radiator parts made
of engineering plastics. It was because of weight and cost
and corrosion resistance and because the suppliers,
material scientists and parts designers believed that
durability would be adequate. Tour any scrap yard and
you’ll see that it’s a perfectly valid decision and helps
recycling. The cars passed testing regimens the old-school
Jags could never have passed, but nothing’s perfect.
I don’t understand why rational people give their cars
names, but I don’t condemn them for it.–
The original message included these comments:
is metal. I don’t understand why Jag apparently decided to
‘‘cheap out’’ and go with a few plastic parts instead of
metal, beginning with the XJ8s (namely that housing and the
In reply to a message from PeterCrespin sent Mon 4 Apr 2016:
Dang, Peter, I thought the ‘‘naming thing’’ was tradition with
Jagers, akin to giving a ship a name? &:-D) Main reason
I’ve done it though is b/c I’ve owned multiple Jags, and it
helps me keep them straight when talking about them to other
people.–
The original message included these comments:
I don’t understand why rational people give their cars
names, but I don’t condemn them for it.
In reply to a message from AttyDallas sent Fri 1 Apr 2016:
Paul…as the ones that have been mentioned but there are a
couple of points that haven’t been mentioned ;o))
The hose attached to bottom of expansion tank.
The hose attached to bottom rear of throttle body.
My own personal experience is that every time I check the
coolant level and top up to bottom of filler neck…it will
puke this to atmospheric catch tank…so, I have found
it’s OK to leave the coolant level about a 1/4’’ below and
all is well ;o)
The only positive way to check for a leak is to do a pressure
check on the system.
I use the bladder type pressure testing kit and pump it up
to about 18psi…which is 3psi above system pressure, then
use a bright LED torch to search for leaks in the known
places…including the heater hoses where they connect at
the firewall and the auxiliary heater pump and valve.
Cheers,
Maximus–
The original message included these comments:
There’s no sign of leakage underneath the car. He reports
there is a strong smell of coolant though around the engine
compartment area (never in the cabin) but he doesn’t see any
wet spots.
Any ideas on this issue?
In reply to a message from Neil Maldon sent Tue 5 Apr 2016:
Neil,
That’s characteristically very kind of you but all of a sudden it
seems so long ago it almost could have been someone else. Like Dr.
Who I tend to regenerate every 7 yrs or so.
Regards
Dr. Why–
The original message included these comments:
Now now Steve DONT be modest, take a bow and change the
Credit from Anon to ‘‘Jagsongas’’
In reply to a message from Jags on gas sent Wed 6 Apr 2016:
I could have probably enjoyed the Dr. Who series if I could
have just understood whatever foreign tongue they were speaking!–
Ross - 89 XJS, 99 XJR, 02 XJ8, 12 XF-R
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In reply to a message from Jags on gas sent Thu 7 Apr 2016:
Well, the results of the leak test are in. According to the
shop, most of the hoses have some degree of leakage in them,
and it will cost approximately $400 or so to r/r the needed
ones. I find this hard to believe, but oh well. (btw, did
Jag do anyway with that PITA ‘‘octopus hose’’ on the bottom side
of the engine in the XJ8s?)–
& Paul '94 XJS 4.0 cp. (
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Sorry I’m late to join this thread. I usually just lurk.
I too had the slow coolant loss on my 98 XJR with some coolant odor and
no puddles under the car. Turns out that the heater hose that connects
to the backside of the water manifold had a tiny leak right at the hose
clamp. Finally found it by pressurizing the cooling system with a test
kit I bought from HF. Although the leak was at the front of the engine,
most of the coolant ran down the valley and dripped off of the back of
the engine.
I changed the right-hand heater hose this past weekend. It is possible
to do this WITHOUT removing the supercharger. If anyone is interested,
here’s how I did it (with assistance and sage guidance from The Wife).
Requires two people (three to remove and reinstall the hood).
Remove hood.
Remove radiator fan assembly. This is necessary to get access to the
belt tensioner.
Remove supercharger belt from top pulley ( no need to remove it from
crank pulley).
Remove water manifold (with thermostat housing intact) by first
disconnecting the temp sensor connector & four hoses.
Remove air intake tube (between air cleaner & throttle body).
Remove throttle body by first disconnecting coolant tank air bleed
hose (the one closest to the throttle body), cruise control vacuum hose,
throttle cable, three electrical connectors and two coolant hoses.
Block off the supercharger intake passage to prevent ingress of
foreign matter using a clean rag, duct tape, etc.
Disconnect the plastic brake booster vacuum pipe from the
supercharger inlet manifold by pressing the collar toward the manifold
and gently tugging on the pipe. On mine, the collar wanted to fall out,
so I set it aside in a safe place.
Release the clamp at the rear end of the heater hose. I clamped
long-nose vise grip pliers onto the hose clamp because my hose clamp
pliers were too bulky to fit into the tight space.
Lubricate the joint where the hose goes over the steel pipe with
WD-40. Using a long screwdriver, long-nosed pliers or other long tool,
work the hose loose.
Have your assistant pull the hose out thru the front of the car.
Take note of the passage from which the hose emerges. Prolific cursing
on the part of all involved is appropriate at this point in the proceedings.
Here’s the tricky part: feed an electrician’s “fish tape” thru the
new hose from front to back. Make sure the tape has no burrs or sharp
edges that could damage the hose. Note the shape of the hose,
particularly the slight S-bend in the middle. Feed the end of the tape
into the hose passage from the front of the car. Make sure that the
tape runs inboard of the knock sensor and emerges from under the
supercharger near the steel pipe to which the hose will eventually
join. It is not necessary for the tape to enter the steel pipe.
Lubricate the outside of the hose (I used vegetable oil) to help it
slide through the tight spaces.
Pushing from the front of the engine, work the hose down the tape,
under the supercharger and it will eventually emerge at the back of the
supercharger, near the steel pipe.
Carefully withdraw the electrician’s tape.
I could not figure out how Jaguar ever installed the spring clamp
over the heater hose at the back end, because the small steel tube and
the bracket are in the way. I punted and used a screw clamp. I’m not a
fan of screw clamps, but in my mind it was the best option here.
Install the clamp over the end of the hose with the screw outboard, and
slide it forward, out of the way.
Using a long screwdriver, long-nosed pliers or other long tool,
position the end of the hose at the end of the steel pipe. Lubricate the
steel tube and use long-nose pliers to slide the hose over the tube.
It’s all downhill from here.
Install the clamp over the hose and cinch down. Make sure the screw
is oriented so it can be tightened if necessary without removing the
throttle body.
Reinstall the water manifold on the front of the engine, using new
O-rings. I used a screw clamp here too on the heater hose.
Reinstall the plastic brake booster vacuum pipe onto the
supercharger inlet manifold by pressing it into the collar (first
replace the collar if you removed it).
Reinstall the throttle body, using a new gasket (I got lucky and
mine was intact from a recent removal for other reasons).
Reconnect all electrical connectors and hoses. Install the click-on
bleeder hoses last because they are fragile and tend to get in the way
of other things.
Reinstall the air intake tube.
Reinstall the supercharger belt.
Refill the coolant. Follow the usual bleed procedure.
I started up the engine, did a leak check and completed the bleed
process before I reinstalled the fans and hood.
Thank you for pointing the header tank tube mix-up issue.
After replacing the LH pre-cat O2 sensor on my XJ8 (and therefore having to remove the header tank), I got really scared seeing coolant leaking under the car in big amounts… I spent a fair amount of time looking around and couldn’t see what was wrong. Eventually, I came here and founnd the explanation in 10 minutes.
Thank you all!
As for the slow leak leaving no traces. I have had that problem! As a matter of fact, the day I bought my XJ8, I was driving back from Belgium to Paris (250 miles) and half way into the trip I had the low coolant warning. Since I had checked the coolant before leaving and the temperature was normal, I decided to drive to the next gas station… and killed the engine.
So since then I am very worried of coolant problems on these cars.
I had the engine replaced and still had to add coolant on a regular basis and sometimes I could smell “hot” under the hood but couldn’t locate any leak.
Finally, I found that this was the thermostat housing pipe at the front of the engine which had a small crack at the line left at junction of the two halves of the mold (definitely a lousy molding - and I am a professional in the field).
Again, this is something I would have found on this site…
Paul '94 XJS 4.0 cp. (
Paul '94 XJS 4.0 cp. (