Prompted by Norman Lutz’s observations on v12 cooling, I have
recently taken a look at v12 thermostats and the aluminium
housings holding them. These are basically the same construction as
the later 6 cylinder engine design and have a spring loaded
blanking plate attached to their underside. As operating
temperature increases, this progressively blocks off the bypass
port leading straight back to the water pump, whilst opening up
water circulation via the longer radiator route. (See Dick Maury’s
artice for how this is different from the earlier ‘‘sleeved’’ type
construction.)
The V12 Etype ROM specifies 82 degree thermostats which should have
a fully open temperature of 93.5 to 96 degrees Celcius.
Both the etype and xjs style housings are machined so that the
depth of the bypass outlet is set at about 41mm. As the thermostat
opens, the plate on the bottom also slowly extends downwards, until
it eventually blanks off the bypass route, or so I thought…
Placing nine different thermostats into a pan of water, I was most
surprised that only three of them opened out past 4 cms. The other
six, with varying degrees of opening, never extended far enough to
guarantee they would fully block off the radiator bypass route.
Anyone who suspects they may have an overheating issue, should test
their thermostats to see whether they will fully divert water to
the radiator rather than allow the recirculation of hot water,
rather than simply test them for ‘‘temperature’’.
I have posted some pictures in the photo album (which will appear
in due course). All of the thermostats pictured are stamped as
being 82 degrees but only 1,4 and 5 definitely open all ‘‘of the
way’’, in this case to 4.3cms.
kind regards
Marek–
MarekH
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from MarekH sent Sat 8 Jan 2011:
Had the same observation on thermostats. the one that worked was a
genuine jaguar part in a jaguar box from OEM parts dealer.
coincidental, I think not.–
The original message included these comments:
the later 6 cylinder engine design and have a spring loaded
blanking plate attached to their underside. As operating
Placing nine different thermostats into a pan of water, I was most
surprised that only three of them opened out past 4 cms. The other
six, with varying degrees of opening, never extended far enough to
guarantee they would fully block off the radiator bypass route.
Anyone who suspects they may have an overheating issue, should test
–
steven phelps vero beach, florida 85 XJ 6
vero beach, fl, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from MarekH sent Sat 8 Jan 2011:
I’ve only ever used the OE units myself Marek but can you tell us
which brands work correctly.–
850225/679,1E21003,2W2001BW,JNAEY3AC100218,SAJNV4841KC156072
HEIDELBERG HEIGHTS, Australia
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Norman LUTZ sent Sat 8 Jan 2011:
Grant Francis sent me a list P#s of Thermostats available here in
the states for proper dimension. Unable to match the AU#s but did
find a Beck/Arnley product #143-0081, there is a Stant part also
same specs. that was not available at the time, (85d)(95d)diff.#
and a Waxstat unit from the UK. $25@ at Kragen Auto Parts/Kelley.
Norman Lutz did advise that the cooler temp. Thermostat could
inhibit temps to the point of Smog-test failure. Best, JW–
The original message included these comments:
which brands work correctly.
–
86XJ-S cpes, Ballet I, Act II, 288 Dana
Fresno, CA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Norman LUTZ sent Sat 8 Jan 2011:
Dear Norman,
Worryingly, 7 out of 9 were Waxstat, made in England
2 were (quite old) West German ‘‘Wahler’’ make.
7 out of 9 thermostats were 3.2cms high (i.e. height from mounting
ring down to the closing plate) and all of them extended at least
to 3.9cms
Of the 3 Waxstats which did extend past 4.1cms, two of them were
3.4cms tall to start with.
I think the general conclusion is that a Waxstat will ‘‘stretch’’ 0.7
to 0.8cms when up to temperature. If you have one which measures at
least 3.3cms high to start with, then that’s good news.
Perhaps either bonding a 1mm rubber washer onto the bottom of the
others or onto the xover pipe port will finesse any potential
problem were one to not be able to get hold of a decent replacement.
See Jag-lovers Forums - Jag-lovers for a brief
discussion of similar concern regarding MotoRad thermostats back in
2007 - Grant Frnacis recommends thermostats from a Ford Falcon.
I’ve had good luck with Gates, and they’re readily available.
I’m intrigued by the arrangement used by Porsche…they use a hard
rubber insert on the bypass passage. This gives a compliant seal for
the bypass poppet, and protects the bypass port from cavitation
damage. These could be made with a little extra height…hmmmmm…
Mike Frank
At 07:07 PM 1/9/2011, you wrote:>7 out of 9 thermostats were 3.2cms high (i.e. height from mounting
ring down to the closing plate) and all of them extended at least
to 3.9cms
Of the 3 Waxstats which did extend past 4.1cms, two of them were
3.4cms tall to start with.
In reply to a message from Michael Frank sent Sun 9 Jan 2011:
When cold, a 3.2cm high thermostat has a gap of just under 1cm to
the bypass port.
Given that the thermostats all open by roughly the same amount and
that the thermostat bypass plate is itself spring loaded with over
half a centimetre of travel (to take up anticipated but never
achieved ‘‘over-opening’’), it seems to me that the way to go is to
make up some inserts, say 2.5mm high, as a press fit into the
housing’s bypass port. I’ll fab up something out of Delrin, which
is inert and has a tiny amount of give. Additionally, Delrin won’t
age the way rubber will. As a press fit, they won’t come out when
cold. When warm/hot, the thermostat will keep them pressed in. If
you switch to 3.4mm high thermostats, the inserts can simply be
levered out at a later date. The thermostat spec will now be no
different to that if 3.4cm high thermostats had been used.
Since all of the thermostats I tested were oem and the same 82
degree spec, (assuming they originally worked) I can only speculate
that with enough heat cycles, the spring loses some compliance with
age and this contributes to any other overheating issues on 4.2 and
5.3 litre etypes once the bypass starts to fail sealing off.
kind regards
Marek–
MarekH
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from jagwit sent Wed 19 Jan 2011:
Dear Philip,
When hot, it will be no different to a working thermostat.
When partially open, it would alter the relative opening between
the two paths in favour of the radiator, cooling the engine quicker
When cold, the water to the bypass will indeed go through a
slightly smaller gap, but there is no other path. The water pump
spins at the same speed so Bernoulli would suggest that it will be
pulled more quickly through the ‘‘restriction’’.
So, I would suspect you first point is more relevant when partially
open rather than when cold.
I hadn’t thought to solder onto the bottom of the thermostat. Other
than ‘‘you can’t take it with you’’, it sounds like a perfectly
sensible suggestion. Tailor the washer to be of such height so as
the thermostat opens to at least 41mm when hot.
If you look at the original photos, the 2 ‘‘Wahler’’ thermostats have
a much wider diameter opening for the radiator than the 7 Waxstats.
That would compound any effect restricting the bypass diameter
would have. Whether that makes things better or worse, I don’t
know. Someone with experience of fluid dymnamics might want to chip
in.
Remember the benchmark is a thermostat which after some age,
eventually never fully closes off the bypass, nurturing persistent
slightly hotter running conditions.
kind regards
Marek–
MarekH
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Michael Frank sent Sun 30 Jan 2011:
Yes Mike, but that’s exactly the point, because they all extend out
by ~8mm, so a 32mm high (i.e. short) thermostat may not block off
the bypass when fully hot.
If they were to extend by 1cm then there wouldn’t be a problem, but
the ones I tested didn’t, hence my sharing this observation.
kind regards
Marek–
MarekH
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Michael Frank sent Wed 2 Feb 2011:
Dear Mike,
It shows Porsche took the point seriously enough to spend a little
more money than Jaguar did to seal off the bypass. A suitably sized
soft rubber grommet/washer over the lower poppet would have the
same effect.
Dear Dan,
if you click on the little white flag to reconstruct the whole
thread, you’ll see what the discussion is about.
kind regards
Marek–
MarekH
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
