I’m following up on a post last year, I’ve overcome air
locks and the system seems to work as specified.
My 3.8S in a hybrid car is getting hotter than I’d like and
on reading the site and other searches I’m inclined to
follow the advise of fitting a bung to the bypass and a
modern high flow thermostat, in place of the sleeved
thermostat.
At idle (800rpm) with twin electric fan on the temperature
ramps up to 90- 95deg, whereas if I increase the revs it
will drop to 85deg, maybe too much is bypassing the
radiator?
Question - any suggestion on the best type of thermostat to
use, plus given the bypass is highly restricted are there
any issues this can create?–
AFD
Melbourne, Australia
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In reply to a message from AFD sent Mon 31 Oct 2016:
I tried the bung, not a lot of difference, what do you get
with no stat in place ?? Are your fans rotating at maximum
?? try a separate feed and see if you have voltage drop as I
had, disconnect one fan and see if the other speeds up…I
also fitted the XJ series three water pump…now no problems–
The original message included these comments:
I’m following up on a post last year, I’ve overcome air
locks and the system seems to work as specified.
My 3.8S in a hybrid car is getting hotter than I’d like and
on reading the site and other searches I’m inclined to
follow the advise of fitting a bung to the bypass and a
modern high flow thermostat, in place of the sleeved
thermostat.
At idle (800rpm) with twin electric fan on the temperature
ramps up to 90- 95deg, whereas if I increase the revs it
will drop to 85deg, maybe too much is bypassing the
radiator?
In reply to a message from AFD sent Mon 31 Oct 2016:
How are you measuring the temperature? Is it really 95 Deg?
Have you measured the exhaust gas at idle and again at the higher
revs when the temp drops? What needles are you using/what else have
you modified/is your timing bang on, and is the dizzy advancing to
spec? You might have needles that are very lean at idle, but a bit
richer at higher revs, your timing may be off, or wandering.
It might be your thermostat… but it might be a host of other
things.
Andrew–
The original message included these comments:
My 3.8S in a hybrid car is getting hotter than I’d like and
At idle (800rpm) with twin electric fan on the temperature
ramps up to 90- 95deg, whereas if I increase the revs it
will drop to 85deg, maybe too much is bypassing the
In reply to a message from JagWaugh sent Mon 31 Oct 2016:
I’ve quite a hybrid, series 3 water pump, 123 ignition,
twin 2 inch SU’s not fully tuned, plus short ‘‘restricted’’
exhaust in order to meet noise regulations. I guess I’ve a
number of issues to consider?
I had hoped to get the water temp down with thermostat and
restrictor and drive it to a specialist for a full set up,
I’m using a pt100 thermocouple under hose at thermostat.
In reply to a message from AFD sent Mon 31 Oct 2016:
Thermostat is spot on opens at 75 fully open at 85.
My thoughts were the 4.2 water pump may pull more water on
the by pass.–
AFD
Melbourne, Australia
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In reply to a message from AFD sent Mon 31 Oct 2016:
My new S3 water pump had double the specified impeller to
body clearance out of the box - a potential source of low
speed underperformance if not checked?–
Simon Ellery S1 XJ6
Kalgoorlie, Australia
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In reply to a message from Michael Frank sent Fri 4 Nov 2016:
Yes, the smaller pulley is a good idea, but what options,
mine I guess is the standard 3.8 litre drive and it is quite
large (slow) any ideas of the options, needing to consider
the belt centre line and cross section too?
In reply to a message from AFD sent Fri 4 Nov 2016:
With fresh everything I’m surprised at your temps if the
block passages were really clean, but they may not be true
temps. Try a second method: IR thermometer at sensor or
thermostat outlet, or sugar thermometer in coolant.
If true temps are you certain any electric fans are
sucking not blowing? Which 123? A lot of their curves are
pretty aggressive and different types have different
static timing. Mixing instructions between Jag manual and
123 might leave you running 10 retarded at idle?–
66 ‘UberLynx’ D, 70 FHC, 79 S2 XJ12L, 97 XJ6L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Sat 5 Nov 2016:
I’m running the 123 with the No. 6 setting.
I plan on fitting a high flow thermostat and partially
plugging the bypass, after that I feel a proper diagnostic
tuneup is warranted before I go too much further, I maybe
over reacting as you say fresh and ‘‘bitsy’’ might be my issue
at this point.
Just concluding, found blockage in radiator which had caused the bulk of the problem, in the mean time installed high flow thermostat and added plug 3/8 hole, to bypass. Only run over 15km or so stop start and under load and 75 degC average, no higher than 85 so at this stage I’m happy.