Oil pressure OK but low pressure warning light on?

[SuffolkFox]

Hi all. I think this may have been covered before but cannot find via search so apologies if repeat. Starting to put the other half's 350i back on the road for the summer and have this problem. Background - the engine was brand new less than 8000 miles ago but ancillaries (including sensors) not, symptoms as follows:-

Start engine, oil cold, pressure sits around 65% of dial

Engine and oil warm up, pressure drops to about 42% at idle and sits dead on 50% at about 2000 rpm

BUT

at idle the low pressure warning light comes on and only goes off if revs raised to said 2000 rpm

SO

- Is there a second sensor that controls the low pressure warning light as pressure seems ok and certainly not horrendously low so could that be duff? If so I can't find it.
- If not is it possible the low pressure warning circuit is giving false info (incorrect pressure switch point)?
- The pressure sensor I can see has a single wire to it so I assume no secondary sensor in there.

Thanks all
SF

[gruffalo]

Yep the light is a diffent sensor I think, sounds like you have a faulty one there.

[adam quantrill]

When the engine is quite hot it's not unknown for the oil light to flicker on idle. What's your idle RPM? Should be about 850. The light should go out above about 1000 whatever happens, so yes, maybe the sensor is duff.

[Wedg1e]

The usual installation features a T-piece screwed into the side of the pump body: the gauge sender and oil pressure switch are fitted into this.
Of course we are talking TVR here so the word 'usual' is open to interpretation...

[SuffolkFox]

Ok, will have a look for the T piece and second sensor later, although couldn't see one yesterday (and yes I am very aware of the TVR interpretation of word usual - based on the various bits on this car and my previous Cerb). It sits at about 900 at idle so that appears OK and once warm light will not go out until above 1500 so unhappy leaving as is. I could try changing the engine oil to see if its the oil volume versus pressure problem but I would think that would effect both readings hence my question.

[gsx600]

Wedg1e said:

The usual installation features a T-piece screwed into the side of the pump body: the gauge sender and oil pressure switch are fitted into this.
Of course we are talking TVR here so the word 'usual' is open to interpretation...

Not seen a wedge with a T piece, usually have 2 holes for sensors, 1 which is just a small sensor that connects to the low oil presuure light (sensor a bit like the water temp sensor), and the other a large affair that connects to the electric oil pressure guage.

On mine at one point I put in a T piece where the oil pressure guage was fitted and then added a capillary type presure guage as could see real time and more accurate. This proved my original electric guage / sensor to be totally wrong

[350zwelgje]

SuffolkFox said:

..... It sits at about 900 at idle so that appears OK and once warm light will not go out until above 1500 so unhappy leaving as is. I could try changing the engine oil to see if its the oil volume versus pressure problem but I would think that would effect both readings hence my question.

Do you know the oil rating? If using less than ..W40, and certainly below ..W30 the oil is too thin for the RV8 when the engine is warm and resulting in a very low oil pressure. Some go to ..W60 to cure it, but that is at the other wrong end of the scale! causing good oil pressure but other issues in the long run.
Changing it for a known viscosity 20W50 (even cheap mineral for the test) would be what I would do to see if it would be resolved by that.

Rob