Fuel gauge!
 

Hi All,

After a number replacement fuel sender units and about 12 years of combined ownership I have yet to witness an accurate fuel gauge do they actually exist in a 240 are do we all tend to fill up and chalk off the miles as though in solitary confinement?

Regards

Scott

They have always been stable giving consistent readings . you must have some kind of problem they are very simple devices .. the main thing is that they are fed with a 10 volt feed , either electronically generated or the older mechanical thermal regulator which gives an average of 10 volts ...
senders rarely if ever give trouble . What have you don as far as fault tracing goes?

Cleans the connections at the black plug and the earth eyelet that are under the black plastic cover under the boot near the spare wheel well. I figured as the other gauges seemed ok the regular should be fine.

The problem is that it seems to float just above the red for a while then back up to the presumed level then as soon as you change speed or direction it'll float above the red again etc. Once the engine is off but with the ignition on the level settles down again.

It was at its worst on the last sender that had me stopping at every petrol station just find out that the tank was almost full, I'd traced that to an actual dry joint at the sender.

Thanks

Scott

The important thing is that the gauge reading should be repeatable - ie whatever it says, it should always mean the same amount of petrol in the tank each time.
Less important is that the reading should be accurate - you can live with one that simply gives the same wrong indication every time.

Mine consistently progresses down the scale in a non-linear fashion. It drops from full to 3/4 in about 10 miles, then very slowly drops to just under 1/2, speeds up a bit down to 1/4, then after 10 miles it's in the red.
This looks alarming, but when the needle really is on empty it suddenly seems to get a new lease of life and is good for another 20 miles. I don't know at what point it actually runs out, I've never dared try for fear of dirt and air locks.

Bizarre but I am used to it. I can also live with the fact that whatever the reading when I first start up, it will have crept upwards by about 1/8 tankfull once the engine gets fully warmed up.
Also it always reads about 1/4 emptier when going uphill.

I think all fuel gauges have their quirks, but that's presumably because they are cheap and primitive. I hate to think what an accurate one would cost - it can be achieved - aircraft fuel gauges obviously have to be very accurate and work upside down or when climbing or diving.

LPG gauges are even more inaccurate - just resetting the trip button on each refill is by far the best method.

I had problems with the fuel and temp gauges on my 79 265, solved by fitting a transistorised stabiliser unit, as recommend by mr Othen of this parish.
Might be an idea for such a modest cost?

Definitely food for thought chaps thanks, I've about half a tank and plan to run it most of the week in readiness for MOT season as with many my reset button is non functioning so will resort to pen and paper.

Scott

The problem could be with the instrument stabiliser - a solid state replacement a is pretty cheap fix - link here:

https://www.volvoforums.org.uk/showp...27&postcount=3

Alan

Thanks for the info Alan about this fuel gauge voltage regulator - I hadn't come across this. It does explain why gauges might fluctuate according to engine RPM etc if the regulator is knackered. Do all 200-series have a 10v regulator behind the dash unit? That old one which has a metal casing seems quite hefty - like it'd take higher amps than the 7810 regulator being substituted in.

Also worth adding - those regulators can be had much cheaper than a tenner - it appears to be a standard 7810 1.5A 10V regulator and currently £1.38 including postage on eb (albeit without the extras that kit comes with). They really do get surprisingly hot, so it's important they are attached to metal as a heatsink (plus providing a ground/negative).
https://www.ebay.co.uk/itm/401349119...Cclp%3A2334524

John

I have been building that electronic regulator into the original can for the last 40 years on various older cars , one pop rivet will hold it to the inside of the can .

Thanks Clan

So - the dashboards from later 100-series to 200-series up to 1980 have that regulator can, which be replaced/modified with a regulator plus small capacitor, see http://www.164club.se/spanreg.html

The 1981 onwards dashboards appear to have the 3-pin regulator as can be seen in the attached image (not mine, grabbed off the web).

While I can't see what the actual numbers are on the OEM 3-pin regulator, it does appear to be effectively the same as a standard 7810 1.5A regulator. It is Volvo part #1362674 - available from Skandix for the scandalous price of €28 for what is a common, generic 20p part if you bought them in any bulk. (Though it is possible that the Volvo OEM unit has extra surge/transient protection circuitry built in because it is a little fatter than a standard 7810).

John