Temperature Gauge false reading.

Discuss Electrical problems here.
FosterS
Minor Friendly
Posts: 25
Joined: Wed Aug 19, 2020 4:49 pm
MMOC Member: No

Temperature Gauge false reading.

Postby FosterS » Tue Jul 20, 2021 3:20 pm

Its a 63 4 door with a 1098 engine the temperature gauge reads way to high, not because the engine is hot as it has yet to be started up today.
I’ve connected the sender up and put it into a beaker of hot water out of the kettle and the gauge is reads over 110 deg C when the water measured with the good ladies toffee thermometer(Shhh) is showing just over 85 deg C. The car had this problem when I bought it a year ago so I bought a new gauge and sender but it made no difference at all, both gauges and senders read the same
The gauge wasn’t wired through the stabiliser, in fact the fuel gauge wasn’t as well, I have now wired it through the stabiliser but the reading is exactly the same.
What am I doing wrong.
Is the gauge meant to be through the stabiliser or not when I bought it it did say that it was for 12 volts and never mentioned a stabiliser at all.
I know the engine is not running at 110 deg C as its not hissing and chucking all the water all over the place.
1963 4 Door 1098cc

Learn from your parents mistakes use Condoms. :oops:

geoberni
Minor Legend
Posts: 2206
Joined: Fri Aug 04, 2017 11:19 am
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby geoberni » Tue Jul 20, 2021 3:55 pm

A quick guess here, but when you say you replaced the Gauge and the Sender, did you replace 'like for like' what you already had?
Because it sounds to me as though you had a mismatch between the 2 items, so replacing with the same ones has just replicated the same problem.
It should NOT need to be on the stabilizer supply (caveat - it depends which gauge you're using).
The purpose of the stabilizer for the fuel gauge is generally to damp out the needle when the tank float is bouncing up and down.

The sender is basically a variable resistor to earth for the gauge. The hotter the sender the more the resistance drops.


A slightly less likely fault is a partial short to earth on the gauge line to the sender, thus throwing the reading out.
How's your wiring?
Good insulation or tatty and perished?
Have you got a multimeter you can use to look for other paths to earth?
Basil the 1955 series II

Image

FosterS
Minor Friendly
Posts: 25
Joined: Wed Aug 19, 2020 4:49 pm
MMOC Member: No

Re: Temperature Gauge false reading.

Postby FosterS » Tue Jul 20, 2021 4:53 pm

geoberni wrote:
Tue Jul 20, 2021 3:55 pm
A quick guess here, but when you say you replaced the Gauge and the Sender, did you replace 'like for like' what you already had?
Thanks for the reply
I bought a kit with the new Smiths gauge and sender in it so it should be matched by Smiths, though I've tried both gauges with both sender units and I get exectly the same reading 110 deg C, i've also run new wiring from the bat right the way to the sender unit same reading.
I'm at a dead end as to where to go next, I've been a mechanic for the past 50 years started in 1966 so I served my time on this era car, got me stumped.
1963 4 Door 1098cc

Learn from your parents mistakes use Condoms. :oops:

Sleeper
Minor Addict
Posts: 820
Joined: Tue Nov 08, 2016 3:18 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby Sleeper » Tue Jul 20, 2021 4:58 pm

I wonder if the temperature of water under pressure has anything to do with it ?

John ;-)

P.S A rheostat/decade box may help and let you know what resistor is needed to calibrate them...

Sleeper
Minor Addict
Posts: 820
Joined: Tue Nov 08, 2016 3:18 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby Sleeper » Tue Jul 20, 2021 5:07 pm

" The purpose of the stabilizer for the fuel gauge is generally to damp out the needle when the tank float is bouncing up and down. "

I think not , as far as I'm aware the function of the stabilizer is to provide a steady/fixed 10 Volts for the instrument in question, rather than it receiving a varying 12 to 14 volts altering with engine revs , ensuring it's accuracy.

The smiths oil gauges working on the same system were internally dampened to achieve this.

John ;-)

geoberni
Minor Legend
Posts: 2206
Joined: Fri Aug 04, 2017 11:19 am
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby geoberni » Tue Jul 20, 2021 5:15 pm

FosterS wrote:
Tue Jul 20, 2021 4:53 pm

Thanks for the reply
I bought a kit with the new Smiths gauge and sender in it so it should be matched by Smiths, though I've tried both gauges with both sender units and I get exectly the same reading 110 deg C, i've also run new wiring from the bat right the way to the sender unit same reading.
I'm at a dead end as to where to go next, I've been a mechanic for the past 50 years started in 1966 so I served my time on this era car, got me stumped.
That is very odd. Many a time we get someone here and it's a miss match because they've brought different types or specs.
I myself brought an old gauge from an autojumble, because I wanted a period Blue/Normal/Red display; but the old gauges have adjustment of the insides to move the pointer datum.


Is there a good earth of the sender, to the engine, to the car body, back to the battery?
With Ign Off, so there's no volts to the Sender, what is the Ohms from the Sender Body to the battery Negative.? Should be practically Zero.
You might have a poor engine earth that isn't significant enough to affect the starter but might be upsetting the reading of the gauge?

You haven't put sealant gunk or tape around the sender?
Just because it's sharing water with the engine doesn't make a good enough earth path.
Basil the 1955 series II

Image

FosterS
Minor Friendly
Posts: 25
Joined: Wed Aug 19, 2020 4:49 pm
MMOC Member: No

Re: Temperature Gauge false reading.

Postby FosterS » Tue Jul 20, 2021 5:24 pm

Sleeper wrote:
Tue Jul 20, 2021 4:58 pm
I wonder if the temperature of water under pressure has anything to do with it ?
I had the sender unit in a beacker of hot water so in this case I think not.
IMG_20210720_144307.jpg
IMG_20210720_144307.jpg (1.9 MiB) Viewed 340 times
IMG_20210720_144415.jpg
IMG_20210720_144415.jpg (1.93 MiB) Viewed 340 times
IMG_20210720_144243.jpg
IMG_20210720_144243.jpg (1.73 MiB) Viewed 340 times
1963 4 Door 1098cc

Learn from your parents mistakes use Condoms. :oops:

geoberni
Minor Legend
Posts: 2206
Joined: Fri Aug 04, 2017 11:19 am
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby geoberni » Tue Jul 20, 2021 5:26 pm

Sleeper wrote:
Tue Jul 20, 2021 5:07 pm
" The purpose of the stabilizer for the fuel gauge is generally to damp out the needle when the tank float is bouncing up and down. "

I think not , as far as I'm aware the function of the stabilizer is to provide a steady/fixed 10 Volts for the instrument in question, rather than it receiving a varying 12 to 14 volts altering with engine revs , ensuring it's accuracy.

The smiths oil gauges working on the same system were internally dampened to achieve this.

John ;-)
it's a bit of each to be honest. But the voltage shouldn't be varying that much, a correctly set up Regulator should be pulsing it at a better rate than that.
The requirement for the stabiliser was a result of the redesign of the gauges to overcome the bouncing around.


https://getrid.my/blog/2018/08/20/volta ... ssic-cars/
Basil the 1955 series II

Image

Sleeper
Minor Addict
Posts: 820
Joined: Tue Nov 08, 2016 3:18 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby Sleeper » Tue Jul 20, 2021 7:56 pm

If you could take the resistance measurements from the sender over the range required , and note the true reading against the gauge reading and tabulate the three readings , I'm sure a resistor could be inserted to compensate...

John ;-)

StillGotMy1stCar
Minor Fan
Posts: 368
Joined: Wed Jun 07, 2017 11:37 pm
MMOC Member: No

Re: Temperature Gauge false reading.

Postby StillGotMy1stCar » Tue Jul 20, 2021 8:38 pm

I think there has been a misunderstanding, the 1/2V(half V) bezel has been interpreted as a 12 Volt gauge.
The gauge is 10 Volts and should have it’s supply through a stabiliser.
As it makes no difference at the moment when the gauge is supplied via the stabiliser suggests the stabiliser is faulty giving an output equal to the battery voltage instead of 10V.
The stabiliser you have is marked with a B (Battery) and I (instrument) and needs to be connected accordingly.
Modern 10V regulators are available, but are polarity sensitive so needs to match your car earth system.

Regards John.

Sleeper
Minor Addict
Posts: 820
Joined: Tue Nov 08, 2016 3:18 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby Sleeper » Tue Jul 20, 2021 9:31 pm

Just spotted , your speedometer is hanging free and does not even have the speedometer cable connected and therefore the stabilizer may not be earthed so will not work ???

John ;-)

P.S. the gauge does not need to be earthed to work properly..

pgp001
Minor Addict
Posts: 693
Joined: Sun Aug 27, 2017 6:05 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby pgp001 » Tue Jul 20, 2021 11:05 pm

You have the sender unit gripped to the metal beaker with a crocodile clip, but is the beaker earthed to the chassis as well ?

Phil P

geoberni
Minor Legend
Posts: 2206
Joined: Fri Aug 04, 2017 11:19 am
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby geoberni » Tue Jul 20, 2021 11:29 pm

Sleeper wrote:
Tue Jul 20, 2021 7:56 pm
If you could take the resistance measurements from the sender over the range required , and note the true reading against the gauge reading and tabulate the three readings , I'm sure a resistor could be inserted to compensate...

John ;-)
I seem to recall, from having worked with these sorts of gauges professionally in my youth, a long time ago, that inserting a resistor will only correct it at one point in it's range, since the relationship between gauge and sender is not a straight line graph but a curve.

And lets not forget that it's a pair of Gauge & Sender as supplied. So poncing around trying to adjust it with a resistor is not acceptable.
My money is on something basic, like a higher than normal resistance earth route via the engine.

All that messing around with a beaker of water, where's the good earth connection back to battery?
Basil the 1955 series II

Image

oliver90owner
Minor Legend
Posts: 1172
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Temperature Gauge false reading.

Postby oliver90owner » Wed Jul 21, 2021 9:15 am

I expect the transducer (the thermistor) should be connected to a stabilised voltage supply. The gauge will have a 12V back-light bulb fitted?

If the car electrics is still dynamo powered, the temperature indication may well be lowered, from higher engine revs (with no other electrical load) to tick-over (with as much electrical load as possible - lights, heater fan, etc). This may be more apparent with a small capacity battery of considerable age.

If on an A/C generator, there may be no difference between those two conditions as the alternator is likely sufficiently energised unless the ‘ign’ light is illuminated.

FosterS
Minor Friendly
Posts: 25
Joined: Wed Aug 19, 2020 4:49 pm
MMOC Member: No

Re: Temperature Gauge false reading.

Postby FosterS » Wed Jul 21, 2021 10:05 am

geoberni wrote:
Tue Jul 20, 2021 11:29 pm
All that messing around with a beaker of water, where's the good earth connection back to battery?
pgp001 wrote:
Tue Jul 20, 2021 11:05 pm
You have the sender unit gripped to the metal beaker with a crocodile clip, but is the beaker earthed to the chassis as well ?
Phil P
The other end of the crocodile clip is attached to the battery earth.
1963 4 Door 1098cc

Learn from your parents mistakes use Condoms. :oops:

FosterS
Minor Friendly
Posts: 25
Joined: Wed Aug 19, 2020 4:49 pm
MMOC Member: No

Re: Temperature Gauge false reading.

Postby FosterS » Wed Jul 21, 2021 10:08 am

Sleeper wrote:
Tue Jul 20, 2021 9:31 pm
Just spotted , your speedometer is hanging free and does not even have the speedometer cable connected and therefore the stabilizer may not be earthed so will not work ???

John ;-)

P.S. the gauge does not need to be earthed to work properly..
There is a jump lead attached to the fixing bracket on the other side but you can't see it in the photo.
1963 4 Door 1098cc

Learn from your parents mistakes use Condoms. :oops:

Sleeper
Minor Addict
Posts: 820
Joined: Tue Nov 08, 2016 3:18 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby Sleeper » Wed Jul 21, 2021 11:07 am

Next step is to ascertain the voltage at the supply side of the gauge , 10v , 12v or other?

John ;-)

FosterS
Minor Friendly
Posts: 25
Joined: Wed Aug 19, 2020 4:49 pm
MMOC Member: No

Re: Temperature Gauge false reading.

Postby FosterS » Wed Jul 21, 2021 4:44 pm

Sleeper wrote:
Wed Jul 21, 2021 11:07 am
Next step is to ascertain the voltage at the supply side of the gauge , 10v , 12v or other?

John ;-)
The voltage in was 12.8v the voltage out without load in 11.8 v the voltage out with a small test light (4w) as a load is 10.9 v so i'm going to get a new stabilizer is there a good one to be had or are they all the same and would an elecronic one be best.
1963 4 Door 1098cc

Learn from your parents mistakes use Condoms. :oops:

pgp001
Minor Addict
Posts: 693
Joined: Sun Aug 27, 2017 6:05 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby pgp001 » Wed Jul 21, 2021 6:05 pm

I added an electronic voltage stabiliser when I did mine, it uses the same sender and gauge as you have. Mine has functioned perfectly for the last three years. The electronic ones give you a steady 10V DC output, the Morris one on the back of the speedo is not really a true regulator as such, it just switches on and off using a bi-metal strip so you get a nominal steady 10V supply for the fuel gauge.

https://www.ebay.co.uk/itm/282642726457 ... Sw9opfhCfU

Phil

Sleeper
Minor Addict
Posts: 820
Joined: Tue Nov 08, 2016 3:18 pm
MMOC Member: Yes

Re: Temperature Gauge false reading.

Postby Sleeper » Thu Jul 22, 2021 7:40 am

Years ago I made a batch of them for the Lotus Club , in the original cases , and they worked a treat , some are better than others ( mine had input and output capacitors ).

Yes, electronic ones are much better than the vibrating contact type , and the above link takes you to Fleabay and there are plenty to be had , but I've not tried any so cannot comment...

John ;-)


Who is online

Users browsing this forum: No registered users and 1 guest