Erratic fuel gauge!

[Borderbmw]

My fuel gauge seems to have a life of its own,it can go from about where it should be,to half what it should be,then past it and then zero! im not sure if its the gauge or tank sender unit....any clues? all the other clocks seem to be working fine

[Brianmoooore]

Take the cluster out and tighten the nuts that hold the gauge in place.

[Borderbmw]

Ill try that,thanks brian

[oneblueleg]

Imagine the picture in my erratic temp gauge thread reflected... same problem I would imagine, as Brian says...

By the way, the thing that stumped me for a little while was how to get the plastic cover off the dash just under the cluster to reveal the screws holding the cluster in... there are two nice aluminium knurled thumb nuts behind the dash that hold it on (one each side of the steering wheel), you need to remove the big cover under the steering wheel to get to them... pretty obvious you might think, but I just expected plastic clips, not nice big aluminium nuts!

[Brianmoooore]

Temp gauge can have the same problem, but a duff SI board can also affect the temp gauge.

[Borderbmw]

Thats what i was thinking,but everything else seems ok,so i was hoping i wouldnt have to change the si board,do you know of anyone selling good used,or refurbed boards? i only know of hartlake in kent

[Brianmoooore]

Enough E30s in scrapyards these days to find one that has had it's board replaced at some time with the later lithium battery type.

[Borderbmw]

Do the batteries look different?

[cros]

Do the batteries look different?

These are the lithium type. They are 1/2 AA size, 3v each.

[Brianmoooore]

AFAIK, there are no issues with this later board, other than the batteries are non rechargeable, and are only used when the board is disconnected from the car battery. How long they would last in a scrapyard without the battery, I have no idea. I've not found an exhausted set yet, but if they do go flat they will need to be replaced.
There is a removable jumper on this type of board that switches the batteries on or off.

[cros]

The lithium cells have a shelf life of about 10 years. In the SI board application they'll most likely die due to old age rather than being drained. New cells are about Ԛ£6 each.

[Brianmoooore]

Happened to have a lithium SI board on the workbench, so I just stuck a meter across the jumper pins. This gave a current drain of 0.025mA.
1/2 AA Lithium batteries (CPC ~ Ԛ£3 each), have a capacity of 950mA/hr, so, 950 / 0.025 = 38,000 hours =1583 days = 4 and a bit years.
Most cars wouldn't spend anything like this long in a scrapyard, but could be a problem with cars that have been stored without a battery as a future project.

[cros]

From Varta's LiMnO2 specs, the cylindrical 1/2AA will run a 25uA load for 4.5 years even with cell ageing. But also they self-discharge to being useless after 7 years at 45deg or ~10years at 20deg even without a load.

I suppose all these are worst-case numbers though, but they suggest any factory fitten E30 lithium battery is over the hill by now.

You're right about the price. I'm remembering a local price in euros. CPC do indeed have them for < Ԛ£3 +vat. A nice cheap way of getting a 'new' SI board.

[Brianmoooore]

The batteries on the board I tried are date coded 89-11, and seem to be completely healthy.

[Borderbmw]

I remember changing the batteries on my old 316 si board for some i bought from maplins on recommendation which seemed to work but i cant remember the specification they were...any clues to what i need to get?

[Borderbmw]

Brian (hope you're out there somewhere!?),ive just taken out the instrument cluster and you said check the gauge securing nut is tight....i would if there was one but its fell off over time! ,and there is movement in the gauge.....so i just need to try and find a tiny nut for it now...

[Brianmoooore]

Nut is 4mm I should think, but don't quote me.
For the batteries- www.cpc.farnell.com , order code BT00170 for replacements for the Ni Cds. These are tag ended 2/3 size NiMH batteries, work fine and give you a bit more room to work. If you want the Lithium batteries, order code BT00119.
Smallorder carriage charges are a bit steep, so have a look around the sight and see if you can make the order up to Ԛ£30 for free delivery.
All sorts of car related stuff on there if you hunt.

[Borderbmw]

Im guessing the lithium are more advisable,my mate (who i got the car from) has changed the batteries for ni-cads but ive put a meter across them and there's no charge in them so i doubt very much if there charged,ill check out the cpc site,thanks Brian.

[Brianmoooore]

You can only use the Lithium batteries in the later board that used them originally. They don't normally ever need replacing.
The NiCd or NiMH are used in the early board.
CPC also have bulbs suitable for replacing the ones in the various switches, bulbs suitable for the OBC,and bat teries suitable for replacing those in the OE BMW alarm.