Thanks for the offer Dave. I wouldn’t know what to do with it. Do you mean strip internals of my current voltage stabiliser and then fit the 7810 inside the shell?

Will have to see. I’m assuming mine is working based on the volt readings jumping around. The next thing I’m going to try is the gauge sensitivity adjustment.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

I'd really like to know the outcome and are the cork plugs present in the adjustment holes in the back of the gauge?
Sounds like your voltage stabilizer is working ok and it has a good earth.
I have the very same issue
I have a new old stock gauge which I could try but interested in your outcome
Cheers

No corks plugs are present. I tried covering the holes with blu-tack but that didn't make any difference. Like someone mentioned, i could try covering the main opening in the firewall (where all the cables go through) and maybe just chuck some rags around the gauge to insulate it further.

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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Minimania in the US has several articles on the instrument voltage stabilizer and how to replace the bimetal strip with a 7810 (and other) voltage regulator. BUT; you have to gut the existing unit and be reasonable at soldering and electronics. If you are not confident, don't!! ONLY use a 7810 regulator with negative earth. I can post one if you are still keen.
Several contributors thought that the airflow through the temp gauge might effect the reading but rapid airflow near the stabilizer might cool down its heated bimetal strip and alter its average output. This would then effect the gauges. Try taping some insulation around the stabilizer.
Another possible problem is a stuck OPEN (or missing) thermostat. (If so, the gauge might actually be correct. Use an infra red gun to check cylinder head and radiator temps. Mine stay near 80c with normal driving.
As you can see in the photo the 7810 regulator drops the battery voltage (12 to 15 volts) to about 10 volts. The metal backing is connected to the negative pin 2 leg and can be bolted to the earthed case of the stabilizer. Pin 1 (red) is soldered to the B battery connection and the Pin 3 (Lucas mostly used light green wiring from the stabilizer to bimetal instruments) solders to the I instrument connection.
I must admit that although the 7810 regulator that I fitted to my car works perfectly, it did not solve the problem of a poorly calibrated fuel gauge. It does give a stable voltage at the fuel sender that I have accessed for a digital fuel gauge with alarm. Dave D

Cheers Dave for some more info.

I have replaced the thermostat but it didn't make any difference to the reading at the gauge.

I need to change the gauge and stabilizer - also checking the earth

so far I haven't been able to resolve the issue of the temp gauge.
I found on inspection that the cork plugs were missing from the back of the gauge so made new one's and fitted and did a test run.
The gauge still read C on the open road but when parked or at low speed read normal.
I then fitted more insulation around the area of the gauge or gauges and then did a road run. No change to the gauge reading. Still reading C on the open road.
I have replaced the thermostat before starting testing.
I have a new gauge and voltage stabilazer so which should I replace first?
The question that I need to ask is shouldn't the gauge remain on N on the open road? at speed.

Firefiery
Get hold of an infra red temperature gun to find the REAL engine, cylinder head, thermostat and radiator temperature and use that to judge how accurate the gauge is. This is much easier than taking out the sensor and dunking it in boiling water (100 degrees) while still wired to the gauge and with the thread earthed to the engine block.
I do a lap of the car after each major run with the gun to check engine, radiator, oil cooler, generator, sump and wheel bearings. I don't know what they should actually read but just pray that they don't change.
Dave D

Firefirey,
I'd put the car on stands at front when up to temp, then run it at 80 or 100 kmh. If temperature doesn't drop it's probably body vibration causing your problem, it's exactly what mine did with the fuel gauge.

Cure- bin the thing and fit an electronic one, it's 2020 now, not 1960.
$25 from 'wombat' on here.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Agreed. All of mine have been converted. I used the LM2940T-10.0 in each case, as covered here:
britishv8.org/Articles/MGB-Voltage-Stabilizer.htm

Still haven't got the temp gauge sorted.
So far I have checked the two cork plugs in the rear of the gauge - one was missing so refitted a new one.
Test run showed no difference to gauge reading.
Replaced the voltage stabiliser and found the earth wire on the gauge was a little loose.
Test run and still the same low reading on the gauge at speed.
Fuel gauge appears to be working fine.
New thermostat was fitted - Gauge still reading low.

If the actual car temp is ok then just adjust the gauge to read higher - http://www.mgb-stuff.org.uk/fuel.htm

These 2 photos show the difference you can get in adjustment at rest.

The first is too low and the second is too high



Edited photos showing the difference in adjustments

Have you used a non-contact thermometer to read the actual temperature of the temperature sender?

I want to update this thread because people have put a lot of info into this.

I generally try to do all I can before buying stuff because you can spend a fortune chasing faults. (You’ve all been there!!!) So I assumed the sender and Smiths gauge were calibrated for each other.

1) first tested the gauge by grounding the temp wire in the engine bay. Gauge needle moved from C to H. Disconnected the grounding wire and the needle moved back to C. Great. Temp gauge works.

2) plugged the two holes on the back of the gauge with blu-tack. Needle still moved from near C to near H during normal driving. Removed blu-tack.

3) Checked earth wires. All tight. Gave everything a bit a a jiggle. Needle still moved to the C and H extremes.

4) reset timing and carb. So tappet clearances, points, checked leads for resistance, checked coil resistance, fiddled with carb jet until all running sweet. Needle still moved quickly but didn’t reach the H extreme.

4) put bulkhead insulation in. The piece that sits on the engine side of the firewall. It covers the big hole where all the wiring and speedo cable comes into the car. Needle still moving to quickly from C to 3/4.

5) cut a piece of 10mm foam to cover the hole. It was quite long... nearly 400mm. Cut a vertical slot to try and seal around the loom. Driving around, I could feel air coming through to instrument cluster (centre 3 dial type). Needle still moving to quickly from C to 3/4.

5) just yesterday, Decided to use an old foam placemat (2mm ish). Cut it to fit the big hole. Cut a horizontal slot in it so it can slide past the loom and so it sits flush against the firewall. Gaffa taped the slot. Got some soft foam to stuff around the wiring loom. Replaced bulkhead insulation, test drive today and bingo!!! Far out. What a process.

Long story short. My problem was air being pushed through the big bulkhead hole and messing with the temp gauge. Also, my timing might have been out and possibly running hot.

Temp gauge now sits in the middle. Thanks everyone for the help.

The. End. Fewwwfff.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Nice work you got to the bottom of the issue.
What temp thermostat are you running - 74 - 82 or 88 deg?

Oh. Forgot about that. I’ve got no idea what temp thermostat is. Next time I’ll check.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.