[xj] thermostats. Opinions please

XJ
1

In view of the higher-than-desirable temperatures in my 1990 V12 last week
(recap: after 3 hours highway driving the temperature would go to 95+ with
AC on. Cutting the AC lowered the temps a bit. Crossing into Canada
immediately brought the temp. to 88-90. I can either keep this car at home,
or try to resolve the problem), I have spent the day replacing thermostats,
which were new and newly installed, and yes, correctly. I am using the usual
82 degree (usual here for the V12, that is) OEM Waxstats. I am still waiting
for one thermostat, but I have removed the two that were in there. I tested
both in a pan with a thermometer (my wife is away; but if the next spaghetti
sauce tastes a bit like antifreeze, I am in trouble).
Here is my question: I assume that an 82 degree thermostat should open
fully at 82 degrees, and not simply begin to open at that temperature. Is
this correct? If so, I had two faulty thermostats (yes, they were marked
“82”); they were not fully open until the water temperature approached 95,
and they did not even begin to open until close to that temperature. This
now has me wondering. Have I now installed an untested (new) 82 degree
thermostat that may also be faulty? The one I get tomorrow will be tested
before installation. Opinions please
And Frank-the-mechanic has okayed the use of Water Wetter in this
engine; he was in fact quite positive and felt that it would have no effect
on any Barr’s Leak that might be in the system (my only concern). So I will
do that, and I will report. The car is being driven to Seattle for a second
concours event on Friday, and the ambient temperatures are supposed to be in
the 30’s (90’s for Americans).

                                            Gregory===================================================

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2

In view of the higher-than-desirable temperatures in my 1990 V12 last week
(recap: after 3 hours highway driving the temperature would go to 95+ with
AC on.

Which isn’t really all that hot, considering the warmish ambient
conditions

Here is my question: I assume that an 82 degree thermostat should

*open

fully* at 82 degrees, and not simply begin to open at that temperature. Is
this correct?

Yes, give or take a degree or two

If so, I had two faulty thermostats (yes, they were marked
“82”); they were not fully open until the water temperature approached 95,
and they did not even begin to open until close to that temperature.

Definately not OK

This now has me wondering. Have I now installed an untested (new) 82
degree
thermostat that may also be faulty? The one I get tomorrow will be tested
before installation. Opinions please

Well, thermostats are mass produced, and cheaply at that. A faulty thermo is
not unheard of, but I’d say the odds are in your favor. If I had to toss out
a wild guess, I’d say 5% are faulty out of the box, at the most. One trick,
though, is to exercise them before installation. Do this by simply using
your thumbs to open the thermo against the pressure of the spring.

Cheers
“Pine Needle” DwyerFrom: “Dr Gregory Andrachuk” V12-VDP@shaw.ca

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3

Gregory It has always been my understanding that the temp rating on the
thermostats state the temperature at which point it starts to open. Not
the temperature that it reaches when fully open.

I was also really concerned about the temperature on my 92 when driving
down to Ottawa a few weeks back. It was a very hot day and like yours,
mine was creeping rather high, well a lot higher than I was comfortable
with. I mentioned this to Jeff Booth when I arrived and he said his 92 was
reacting exactly same as mine. At 130 kph it was coming up to the 100 mark
so I kept backing off so as to keep it down around the 95 degree mark.

Bob.> In view of the higher-than-desirable temperatures in my 1990 V12 last week

(recap: after 3 hours highway driving the temperature would go to 95+ with
AC on. Cutting the AC lowered the temps a bit. Crossing into Canada
immediately brought the temp. to 88-90. I can either keep this car at
home,

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4

In reply to a message from Dr Gregory Andrachuk sent Wed 21 Jul 2004:

I would really get the lowest temp. thermostat, like 180F
for summer on that engine. It would even be OK in winter,
as long as it reaches the middle on the gauge. I have a
180 deg. thermostat from checker auto, and it works fine.
Engine heats up fast, and gauge stays on the left side of
normal, when the AC is on the temp creeps up to not quite
the ‘‘L’’ on the gage, and fans come on, but cools down
quickly after that. This is on a XJ6. Outside temp. today
98F deg. here in albuquerque. 95C on your engine is nothing
to worry about as long as coolant is present, and stays
at that location on the gage.
Walter–
69E / 78XJ6 / 73 VW Ghia
albuquerque/new mexico, United States
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5

In reply to a message from Dr Gregory Andrachuk sent Wed 21 Jul 2004:

Gregory:

My '88V12 ran happily in the 88-90C range until ambient temps
reached the 100+F area (38C for ROW), Then, there were times it
would approach 95C. Even at 85mph it really never really got over
that mark. In the fall, I had the radiator rodded, thermostats
(82C) replaced, new black plastic more efficient fan, and coolant
hoses done.

This summer, she happily purred along at '88-90C until once again
the temps reached about 95F, However this time she would only get
to about 91-92C on the gauge after sitting in traffic. After the
water Wetter thread a few weeks ago, I decided to try a bottle.
Yesterday we hit 100F outside, and since I added the Water Wetter,
I have not seen the 90C mark on the gauged touched. I beieve I am
getting about a 3 degree C decrease from the Water Wetter. I am
running about 50/50 mix of water and anti-freeze. Next summer I may
try the 75/25 mix to maximize the affect of the Water Wetter. So,
so far I am pleased with it.

Cheers–
The original message included these comments:

 And Frank-the-mechanic has okayed the use of Water Wetter in this

engine; he was in fact quite positive and felt that it would have no effect
on any Barr’s Leak that might be in the system (my only concern). So I will
do that, and I will report. The car is being driven to Seattle for a second
concours event on Friday, and the ambient temperatures are supposed to be in
the 30’s (90’s for Americans).
Gregory

–
Larry Karpman '88 V12 SIII, '94 MX-5
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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6

Thanks Walter. On the V12 especially it is important to use an OEM
thermostat with a “jiggle pin” to allow the purging of air from the system,
so an auto-shop special won’t do. I agree that 95 is not in any way
dangerous, but long term use above that temperature is just harder on
everything. It makes the wiring brittle, al the rubber ages more
quickly…the xj6 does not run as hot as the V12. I only heard my electric
fan run once on an xj6!
Gregory----- Original Message -----
From: “W. Schuster” ewsch@joimail.com
To: xj@jag-lovers.org
Sent: Tuesday, July 20, 2004 7:15 PM
Subject: Re: [xj] thermostats. Opinions please

: In reply to a message from Dr Gregory Andrachuk sent Wed 21 Jul 2004:
:
: I would really get the lowest temp. thermostat, like 180F
: for summer on that engine. It would even be OK in winter,
: as long as it reaches the middle on the gauge. I have a
: 180 deg. thermostat from checker auto, and it works fine.
: Engine heats up fast, and gauge stays on the left side of
: normal, when the AC is on the temp creeps up to not quite
: the ‘‘L’’ on the gage, and fans come on, but cools down
: quickly after that. This is on a XJ6. Outside temp. today
: 98F deg. here in albuquerque. 95C on your engine is nothing
: to worry about as long as coolant is present, and stays
: at that location on the gage.
: Walter

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7

In reply to a message from Larry Karpman sent Wed 21 Jul 2004:

A common test I’ve heard about is to cook/boil the
thermostat on the your kitchen range in a pot of water and
monitor the temperature, watching for the opening point.
Nobody does this much with American cars as the units are so
cheap and temperature is not as critical as it seems to be
here. I believe the rating is for opening not fully open. It
may equate to the same thing concerning coolant temperature.
You could try a run without the thermostat in the engine. If
it overheats then, your problems are elsewhere (radiator,
airflow, etc.).

Kim Hall
Everett, WA
1987 XJ6 VDP
AKA Hall-O-Grafix–
The original message included these comments:

In reply to a message from Dr Gregory Andrachuk sent Wed 21 Jul 2004:
My '88V12 ran happily in the 88-90C range until ambient temps
reached the 100+F area (38C for ROW), Then, there were times it
would approach 95C. Even at 85mph it really never really got over
that mark. In the fall, I had the radiator rodded, thermostats
(82C) replaced, new black plastic more efficient fan, and coolant
hoses done.
This summer, she happily purred along at '88-90C until once again
the temps reached about 95F, However this time she would only get
to about 91-92C on the gauge after sitting in traffic. After the
water Wetter thread a few weeks ago, I decided to try a bottle.

–
Kim Hall
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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8

In reply to a message from Peddlarbob@look.ca sent Wed 21 Jul 2004:

I concur with Bob on the opening of the thermostats. They will
remain closed until the coolant temperature reaches the temperature
rating of the thermostats. If a thermostat were to start opening
before this, the coolant temperature would never reach the ‘‘rated’’
temperature as the coolant would begin circulating and cool down
even further.

When does it open fully? From what I recall, it is rather quickly
and within a few degrees above the thermostat rating (3 or 4
degrees if memory serves me correctly). Last year when I had the
distributor overhauled to correct a sticking vacuum advance
problem, I realized that the thermostats were faulty as I could not
get the coolant temperatures to go over about 75 degrees (!!!).
This was after recoring the rad, replacing the coolant hoses and
fan/coupling and flushing out the block. When I purchased the 88
degree Waxstats from the dealer, I checked their operation using
the pot-on-the-stove and candy thermometer method (with the
blessing of my wife) to make sure that they were not defective.

On the way back from the Ottawa Concourse, I also did about 130 kph
without running the A/C and my guage did not go over 91 degrees. I
am convinced that with a properly functioning system, there is more
than ample cooling capacity in the Jaguar system and that the
coolant should be within a few degrees of the thermostat rating.
But then again, I haven’t been to Texas or to the Oregon
Triangle…–
The original message included these comments:

Gregory It has always been my understanding that the temp rating on the
thermostats state the temperature at which point it starts to open. Not
the temperature that it reaches when fully open.

–
Victor Krisel, '85 ser.III V12 Vanden Plas
Toronto, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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9

I assume that an 82 degree thermostat should open
fully at 82 degrees, and not simply begin to open at that temperature. Is
this correct?

Gregory, in my experience the thermostat begins to open at the specified
temperature and is not fully open until another 5degC or so. The devices
show significant hysteresis: they close about 5degC lower than they open.
Also they can be a bit stuck when first testing a new one so the opening
temp can get quite high, but then they settle to a consistent opening temp.

There is a wide spread of production tolerances here too - so don’t take
the 82degC too seriously! It can be +/- 4 degrees. Best to test the new
units - I guess you can return failures?

Chris

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10

In reply to a message from Chris Knowles sent Wed 21 Jul 2004:

I agree it’s an opening threshold temp that is cited for Tstats.

The problem IME with the pot on the stove method is timing. It is
only really any good for seeing if the thing works or not, in very
approximate terms.

It is very difficult, if not impossible, to increase saucepan temp
step-wise and observe the behaviour of the Tstat at each increment
before moving on to the next temp step and letting it stabilise to
check behaviour there before moving to the next etc. If it were
possible to do that then we could believe the results we get and
plot an accurate graph of temp versus Tstat condition, but it isn’t
unless you have a much more accurate and progressive stove than
mine. In practice what tends to happen is that the pan of water
increases in temp pretty quickly and in a continuous smooth curve
over time. The average sugar thermometer tracks this quite well as
it has a low latency and so we monitor the water temp fairly well.

Meanwhile, we try to eyeball the Tstat which is much slower to
react, so almost inevitably the very process of noticing it opening
is spread over several degrees of water temp and we never hold the
temp steady enough to see if given time the Tstat would fully open
at that temp. Instead by the time it has reacted and is fully open,
the temp has climbed another X degrees and we see that as cause and
effect, where in truth the Tstat may well have opened fully at the
temp it first started opening (especially wax ones) had we held
that temp for a while.

Bear in mind also that in a pan of water there is no differential
temp or pressure of coolant in either direction, and so we end up
with a fairly crude approximation of what is happening in the
engine. So apart from seeing if it works or not, and maybe
comparing to differently-rated Tstats side by side, I wouldn’t put
too much store by the actual saucepan figures per se. I don’t cook
my vegetables in a calibrated water bath, nor really calibrate my
Tstats in a saucepan…

As far as overheating is concerned, provided the engine cycled back
down to an acceptable range each time it climbed under heavy
thermal load I’d be fairly relaxed about it. Climbing unchecked, or
climbing under light load are something else. And as for the actual
temp, I’d give a large leeway to any auto gauge reading and the
system is designed to cope with over 100C anyhow.

Meanwhile, the difference to wiring longevity from operating at,
say, 100C versus 90C would be pretty insignificant I expect. I’d
imagine the big ageing/embrittlement effect comes from running for
long hours at 90 or whatever, not spells at 100 instead of 90.
Unless maybe one of our plastics experts can point to some kind of
threshold effect here too, short of the actual melting point due to
touching hot exhausts or an electrical short, or high-resistance
faulty connection?–
Peter Crespin 94 X300 Daimler / 66 2+2 ‘E’
Buxton, United Kingdom
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11

I agree. I’ve heard of some V12 guys buying several thermos, testing them
all, and then installing the two which are most closely matched in terms of
opening temp and fully-open temp.

My own experience in testing them was that the rated temp and the fully-open
temp was much closer than some of the others have mentioned. But, that was a
long time ago… and not with WaxStats.

Doug Dwyer
Longview, Washington USA
1987 Ser III XJ6
1988 XJS V12From: “Chris Knowles” cspknowles@zoom.co.uk

There is a wide spread of production tolerances here too - so don’t take
the 82degC too seriously! It can be +/- 4 degrees. Best to test the new
units - I guess you can return failures?

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12

In reply to a message from Doug Dwyer sent Wed 21 Jul 2004:

And the temp reading from the thermometer might vary if the bulb is
resting on the bottom of the pan too, as opposed to being held in
the water near the thermostat bulb. When you think there are heavy
cast iron pans, aluminium ones, paper thin thrift-store stainless
milk pans, laminated sandwich bottoms etc etc. it’s amazing
anything goes right. Point contact on an uneven red-heat electric
ring, versus a soft gas flame on a thick bottom etc.

Sorry, getting carried away there… :-)–
Peter Crespin 94 X300 Daimler / 66 2+2 ‘E’
Buxton, United Kingdom
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13

Also, a regular, non-jiggling thermo can be used by simply drilling a 1/8"
hole in the rim and be sure that’s at the top when the thermo goes in. The
jiggler is good to keep crud moving through the hole, but we don’t allow crud
in our engines anyway, right? :]

By the way, since the sensor for the aux fan(s) is at the bottom of the rad,
it rarely sees the same temp as the upper area and fans, plus it’s set to fire
at 95C, so rarely closing is its life.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Dr Gregory Andrachuk wrote:

Thanks Walter. On the V12 especially it is important to use an OEM
thermostat with a “jiggle pin” to allow the purging of air from the system,
so an auto-shop special won’t do. I agree that 95 is not in any way
dangerous, but long term use above that temperature is just harder on
everything. It makes the wiring brittle, al the rubber ages more
quickly…the xj6 does not run as hot as the V12. I only heard my electric
fan run once on an xj6!

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14

Like anything, a measurement of this sort needs doing right. But, since the
tolerances involved in the thermos themselves are poor, a couple of degrees F
error isn’t a big problem. The thermometer to use is indeed one with a
smallish end and it’s important to keep it against the thermo, in the vicinity
of the core plug – a rubber band is good. I think most folks realize this
and that the temp rise must be pretty slow, so the thermostat’s bulk is always
at about the same temp as the thermometer’s tip. Even on an electric stove,
it’s quite possible to achieve slow temp rises, and if it’s a worry, just drop
an old slug of lead or an old brake pad in the bottom of the pot. Then the
thermo’s mass will be, to use a technical term, mouse nuts, in comparison. :]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Peter Crespin wrote:

In reply to a message from Doug Dwyer sent Wed 21 Jul 2004:

And the temp reading from the thermometer might vary if the bulb is
resting on the bottom of the pan too, as opposed to being held in
the water near the thermostat bulb. When you think there are heavy
cast iron pans, aluminium ones, paper thin thrift-store stainless
milk pans, laminated sandwich bottoms etc etc. it’s amazing
anything goes right. Point contact on an uneven red-heat electric
ring, versus a soft gas flame on a thick bottom etc.

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16

John,

your post made me feel like in Doc Brown’s DeLorean … Alex Cannara and Gregory - who is still around occasionally;-) I think the question has been answered in the meantime … Anyhow your info is appreciated - if only as a follow-up.

Cheers

Jochen

75 XJ6L 4.2 auto (UK spec)