fuel & temp gauge reading to high.

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Paul Jorgensen
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#1 fuel & temp gauge reading to high.

Post by Paul Jorgensen » Tue May 14, 2019 2:35 pm

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Hi All,

Ever since I have had my car, the temperature gauge every now and again has crept up as shown in the first picture, which to be honest was worrying. I did all the usual checks and could not find anything obvious.
In the end I purchased an infrared laser thermometer which I carried in the car, when the temperature crept up I would pull over and check the temperatures around the engine. All was reading normal.
In time I noticed that when the temperature gauge went up so to did the fuel level in my tank... I wish!!!! but the gauge did. That's when I thought, maybe it was the voltage regulator, I replace the regulator and it is still the same.
Although I know it is not overheating it still is worrying when it happens. Not sure if it would make any difference but it has a dynamator fitted in place of the dynamo.
Could anyone offer any help to overcome this problem or have had similar experiences.

The 2 pictures were taken last night on my way back home from its Mot test. The next 2 pictures were taken a few minutes later, I was sat in traffic and the Ammeter was reading - charge
Thanks
Paul
Paul. 1962 Series 1 roadster 850543
1965 mk 1 Lotus Cortina
1973 Triumph Stag (had it since 1982)

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Paul Jorgensen
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#2 Re: fuel & temp gauge reading to high.

Post by Paul Jorgensen » Tue May 14, 2019 2:39 pm

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Paul. 1962 Series 1 roadster 850543
1965 mk 1 Lotus Cortina
1973 Triumph Stag (had it since 1982)

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cactusman
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#3 Re: fuel & temp gauge reading to high.

Post by cactusman » Tue May 14, 2019 5:03 pm

If they both drift up it may be the voltage regulator. The traditional one switches the 12 volts On and off to provide an average 10 volts. To measure it you will need an analogue meter (an AVO meter is the best). Best thing is to replace with a modern electronic version....readily available or build your own....you need a low drop out 10 volt regulator chip....e.g. LM2940-10 plus a couple of capacitors...
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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#4 Re: fuel & temp gauge reading to high.

Post by Paul Jorgensen » Sun May 19, 2019 9:02 pm

Thank you for your reply cactusman, where cam
N I purchase one for a positive earth car
Paul. 1962 Series 1 roadster 850543
1965 mk 1 Lotus Cortina
1973 Triumph Stag (had it since 1982)

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#5 Re: fuel & temp gauge reading to high.

Post by cactusman » Sun May 19, 2019 9:17 pm

Positive earth car..then the chip I suggested is no good. You will need a -10 volt low drop out regulator. They do exist but are rare...you need this one....
https://uk.rs-online.com/mobile/p/low-d ... s/1025700/

Lm2940T-10.0/NOBP. Both the input and output line need a 100 nF ceramic to ground. The output should also have a 10uF electrolytic capacitor to ground....

Do also be aware that the pin outs of negative regulators (needed in positive earth cars) differ.from positive regulators. The mounting tab is NOT connected to ground and they are more prone to instability if not appropriately bypassed with capacitors....do refer to the data sheet when connecting.
.
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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#6 Re: fuel & temp gauge reading to high.

Post by Paul Jorgensen » Tue May 21, 2019 1:03 pm

Thank you again for your reply, I have looked on the RS site and to be honest I am totally confused, would you be able to provide part numbers and maybe a diagram of how to make the unit.
Sorry to be a pain!!!
Cheers
Paul
Paul. 1962 Series 1 roadster 850543
1965 mk 1 Lotus Cortina
1973 Triumph Stag (had it since 1982)

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Tony
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#7 Re: fuel & temp gauge reading to high.

Post by Tony » Wed May 22, 2019 6:50 am

I maybe barking up the wrong tree here but I had a similar problem and it was solved by replacing the old voltage stabilise behind the dash for a electronic voltage stabiliser from SNG, for a positive earth car which was quite cheap. May not be the same issue but it is a 5 minute job. Feel free to blow me out of the water if I am getting confused. One of our forum member did the job for me at Bicester a couple of years ago. Never had any problems since.
Tony (E typed)

1962 E Type Series 1 Roadster (OTS)

Tony

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#8 Re: fuel & temp gauge reading to high.

Post by cactusman » Thu May 23, 2019 3:56 pm

The SNG unit will fit just fine....it probably has the regulator I suggest within.....or it is a fairly easy job to scrape the mechanical innards out of your reg and fit the electronic components within....that's what I did....paul....pm me and I will do my best to send you the circuit diagram!
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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JerryL770
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#9 Re: fuel & temp gauge reading to high.

Post by JerryL770 » Mon May 27, 2019 2:51 pm

Do you have the part number for this improved version voltage stabiliser as SNGB parts catalogue for both S1 and S2 cars say part no: 148876J is no longer available and offers no alternative.
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats
2008 MX-5 NC PRHT

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#10 Re: fuel & temp gauge reading to high.

Post by cactusman » Wed May 29, 2019 6:22 am

LM2940-10NOBP is the wrong part....bear with me.....Will get the correct one!!!
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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#11 Re: fuel & temp gauge reading to high.

Post by Paul Jorgensen » Tue Jun 02, 2020 6:15 am

Last year I fitted an electronic voltage stabiliser after the intermittent high readings I was experiencing.
Everything was fine until Sunday when I took my car out for a run.
As soon as I started the engine the temperature gauge went straight to hot. I drove a 105 miles and only once for a few minutes did the temperature drop to normal whilst driving.
Last night I switched the ignition on and the temperature gauge went straight to High, I removed the wire to the sender and no change. I removed the wire from the temperature gauge and still no change. Only when I remove the wire from the gauge, ( the one from the voltage stabiliser) did the gauge drops to zero which is what you would expect.
Does anyone have any ideas before I go any further.

Cheers
Paul
Paul. 1962 Series 1 roadster 850543
1965 mk 1 Lotus Cortina
1973 Triumph Stag (had it since 1982)

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#12 Re: fuel & temp gauge reading to high.

Post by Paul Jorgensen » Tue Jun 02, 2020 9:53 pm

After pondering about the possible cause of my gauge going straight to hot when the ignition is switched on, Tonight I removed the Gauge from the dash, reconnected the wires and with the gauge in my hand I switched on the ignition and the needle didn’t move, I then earthed the body to the dash and the needle went straight to hot.
Long story short... the wire between the posts in the gauge was touching the body.
All now working properly again 😁
Paul. 1962 Series 1 roadster 850543
1965 mk 1 Lotus Cortina
1973 Triumph Stag (had it since 1982)

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