Fuel gauge
 

My fuel gauge is reading half way no matter how little or how much fuel I put in. Any ideas what it could be would be much appreciated

Hi
float could be stuck
take wire of sender in the boot
should read empty
earth wire should read full
if float stuck take out and fix

Thank you for your reply. Is it located in the central of the tank ?

Yes think there are two types from memory.

Does the engine temp gauge work? If not it's probably the voltage stabilizer/regulator thingy in the instrument panel as it is used for both the temp and fuel gauges. The previous owner had that issue with my car before I bought it.

It should be easy to access the sensor once you remove the masonite / hardboard tank covering that forms the floor of the trunk. As I recall the resistance range on the sender on my 1971 140 is 70 ohms (empty) to 10 ohms full. As noted by grumpydad, pulling the wire off the sender should cause the gauge to read empty. If it does, then the sender is likely faulty. You can confirm that the gauge works by connecting a 68 ohm resistor beteen the sender wire and ground (should read empty) and then a 10 ohm resistor between the sender wire and ground (should read full). If you need a new sender be sure to get he one used for you model year. Volvo used at least 3 different senders on the 140 and they do not interchange.

If the gauge appears to be faulty, do as burdekin advises and check the temperature gauge. A flakey fuel gauge and temperature gauge points towards a bad voltage stabilizer. However, it would be unusual / difficult for a stabilizer to fail in a mode where it gives a continuous 1/2 tank reading.

Thank you so much guys really appreciate all your advise. Makes owning such a lovely old Volvo much more enjoyable 👍

Anyone know where we can source replacement voltage stabilisers ? Thanks

Reproductions no longer appear to be available. Skandix (and Classic Volvo) offers a rebuild service; but, you have to supply an original to get the horrendous core charge back

https://www.skandix.de/en/spare-part...lizer/1021371/

At that price I would be inclined to fabricate a stabilizer. Either from one of the LM series 5 volt 3 terminal regulators (with a heat sink) or using a microcontroller to switch a MOFSET to give you a PWM modulated output of 5 volts - which is effectively what the existing stabiliser is. Should be able to do it for less than $10 Cdn $. If you search using Google you can probably find a replacement circuit that somebody has already cooked up. I would volunteer; but, the weather here has recently switched from deep winter to balmy spring so I am currently disinclined to spend time in the basement workshop. If it starts raining, then maybe!

May be Ebay might yield a used one. Note that you need to check part number. Early 140s (at least up to my 1971) used a 5 volt stabiliser. I think the '73 and later 140s used a 10 volt stabiliser.

This is good advice.

The original instrument voltage regulator was defective when I bought the RB (a 1980 244) so I replaced it with a solid state item such as 142 Guy suggests. Mine came in a little kit with a 10v stabiliser, a heat sink and so on for less than a tenner. This link has the details:

https://www.volvoforums.org.uk/showp...&postcount=383

... if you have an earlier 140 you would need the 5v alternative.

Good fortune,

Alan

PS. If you are a little bit handy with a soldering iron you could probably save a fiver by getting just the component (just google LM7805 or LM7810) - and making up a little loom and a heat sink from some bits and pieces.

Well there you go!

https://spiyda.com/instrument-voltag...lizer-kit.html

For the 5 volt option it will be really important to mount the voltage regulator on a good heat sink. When the tank is full the sensor resistance is 10 ohms which means a sensor current of about 5volts/10 ohms = 0.5 amps. If your charging system is up to snuff the running voltage will be about 14 volts. That means that the voltage regulator has a voltage drop of 14 - 5 = 9 volts. The power dissipated by a linear voltage regulator will be 9V x 0.5A = 4.5 watts which in a tiny package means that it will be getting very hot.

You might want to try this thing instead

https://www.amazon.ca/Converter-Ajus...37512675&psc=1

It is a class of device known as a buck regulator. The only down-side is that it has an adjustable output so you will need a voltmeter to set the output to 5 volts. It is claimed that it can supply up to 3 amps so it should be able to supply the fuel and temp gauge circuits easily. Its up side is that it has a very high efficiency so heat dissipation should be less of an issue and its small enough that you could probably attach it to the existing stabilizer mounting board and use the existing mounting point. Plus, you get two of them for less than the cost of one of the Spiyda linear regulators.

Here is exactly the same thing on same for the cost of a package of chewing gum

https://www.amazon.ca/Lysignal-LM259.../dp/B074J4NXCM