Oil level reading fault

[Ian Comerford]

For a long time when I turn the ignition on/start the car the oil level gauge needle goes straight to the very top of its arc.  I always use the dipstick anyway but am doing some work in the area of the oil tank in the next month or so and thought it might be worth addressing.  The question is, what is at fault, is it;
a) The cork gasket between the sender and tank having failed/tightened too much causing an earth fault

b) Faulty sender

c) Faulty gauge

d) Something else

Thank you

[Nige]

Same here Ian, there is my thread somewhere with some good testing suggestions from the crew.  I've not solved it yet other than disconnecting the gauge.🙃

 

I've even ran wires externally direct from the sender to the gauge and it's still tops out the needle.  Next step is the sender itself.

[Ian Comerford]

Thanks Nige, appreciate the reply.  I seem to recall something ages ago suggesting that if the cork gasket was broken or tightened down too much it’s causes the gauge problem we are both experiencing.  So if that is true you running wires from the sender to the gauge will still exhibit the same issue won’t it.  I’m thinking I replace the gasket first but am waiting for someone with greater experience of electrics than I (doesn’t take much…) or who has fixed this exact issue to reply.

[Nige]

Just make sure everything is spotless around the sender before you remove it, you don't won't any debris in that oil tank.

Not sure how the cork gasket works because surely the nuts and bolts that pass through the sender earth the unit anyway?

Edited July 3, 2025 by Nige

[Ian Comerford]

That’s a really good point……..  I just thought that if the sender was dead it wouldn’t read anything, rather than going straight to the top of its arc?

[PeterK]

Several sensors in the 911 read max if disconnected (oil pressure, etc)

 

If the earth to the oil level (separate earth, linked to the rear light harness) is poor, the gauge will max out

[Ian Comerford]

Thanks Peter, that’s useful, something else worth checking.  

[angusb]

13 hours ago, Ian Comerford said:

For a long time when I turn the ignition on/start the car the oil level gauge needle goes straight to the very top of its arc.  I always use the dipstick anyway but am doing some work in the area of the oil tank in the next month or so and thought it might be worth addressing.  The question is, what is at fault, is it;
a) The cork gasket between the sender and tank having failed/tightened too much causing an earth fault

b) Faulty sender

c) Faulty gauge

d) Something else

Thank you

What`s needed is a Voltmeter , with a Continuinty buzzer setting , ana a couple of leads with croc clips.

 To test the Cork gasket, disconnect both wires oil sender. Touch the earth spade & the oil tank  with meter. If continuinity then gasket has failed, The correct gasket is thicker than the one aftermarket/petrol tank one.

  Gauge- with wires disconnected turn ignition on, the gauge should not move. Now touch earth  with the power wire (the one which has the rubber bung on it) , the gauge should immediately shoot to max,

  To test the earth wire cable, use the same method as gasket. The wires are coated with fibreglass type resin, be gentle, as this cannot be soldered if the spades detatch from the wires.

Unless the internals of the sender are stuck; on,  my car freed off with potholes enroute to bodyshop, then the gauge will work

                                                                                                                                          

  

[Ian Comerford]

Thanks Angus, this seems to cover all aspects, really appreciated.  Just need to find a neighbour with the continuity buzzer voltmeter.  I’ll update once I figure out what’s at fault.

Nige - looks like the cork gasket is a likely suspect after all

[ChesterJLampwick]

My level gauge has always been up the pictures, mostly it reads off scale high, but occasionally works properly with a sudden click, then clicks and goes high again. I've checked the external connections, nothing loose.

Thanks for the testing guide. One day I'll get round to it, just for peace of mind, but I do try and remember to dip the tank every time it comes home hot. Sometimes I look at the dipstick when cold and there is alarmingly next to nothing on it, however it is easy to overfill when I see this, next time its hot it is above maximum. I did have an early CB750 Honda where this meant a worn oil pump or a sticking check valve if the tank drained into the sump while standing.