Oil pressure gauge

[Big Jim]

Good morning .
I have fitted a replacement green breather valve and removed the cam covers to re paint and seal .
I now have a problem with the oil pressure or as I suspect the gauge .I started the engine and did not take note of the oil pressure .When I did notice it ,it was off the scale . With engine off , but ignition on it was still off the scale . Looking in the engine bay I noticed I had knocked off a wire from the sender . This improved maters .Ignition off = zero ,ignition on it does not seem to drop below 30 psi . Engine running , off the scale . I have a non standard cheap gauge , which I always thought read very high , about 75 psi which I put down to a miss match . Do you think I have just damaged the gauge ? Do you know how to take an electrical reading from the back of the gauge ? What type of after market gauge is ok as a replacement ?

[Big Jim]

Update
I have disassembled the gauge and moved the needle back to zero .It is probably how it was before .But it would be good to know what the oil pressure actually is accurately . So still looking for a gauge that will work with my setup .

[amarshall]

The sender and gauge are matched - either a 5 bar or 7 bar pair depending on age and model. Looking at dash, age and model I think yours should be the 7 bar version, which is a VDO to match the rest of the instruments. They're hard to find - best to try Lotusbits or Bauke Tocus I think.

[Big Jim]

Thanks for that .
Just spoke to PNM . According the the VIN it should be 5 bar . He said that the gauges were hopelessly inaccurate and should only be used to indicate a change from the norm . As my gauge now gives me a reading I will not worry bout it too much .
Jim

[amarshall]

Thanks for that .
Just spoke to PNM . According the the VIN it should be 5 bar . He said that the gauges were hopelessly inaccurate and should only be used to indicate a change from the norm . As my gauge now gives me a reading I will not worry bout it too much .
Jim

Thinking about it, that's a pretty good summary of how I use it : something like this : / = normal
something like this : \ = too hot or level a bit low
and if it's \ and flicking up and down a bit, I need to put some oil in it NOW!

P.S. - knocking the wire off the sender won't have done any harm to the gauge.

[Hawaiis0]

Open circuit = no deflection, Short circuit = Full scale deflection(FSD).
It's possible you had momentarily shorted out the gubbings to give the FSD when powered up.

[amarshall]

Open circuit = no deflection, Short circuit = Full scale deflection(FSD).
It's possible you had momentarily shorted out the gubbings to give the FSD when powered up.

Nope. The pressure sender is a variable resistance connected to earth and the gauge is fixed resistance also connected to earth. Effectively, it's a potential divider with a variable resistance in it and the potential being supplied to mid-point between the two loads.

Disconnecting the sender results in an infinite resistance so the gauge gets a full 12V across it (as there is no other path to earth) which is within spec. (just).

With the sender connected, the sender has a low resistance at high pressure, so more voltage sits across the gauge (Kirchoff's law). As pressure drops, the resistance rises, so more voltage appears across the sender and less across the gauge.

The temperature gauge operates in a similar fashion.

[CID]

I always rely on a mechanical gauge (see http://www.ebay.com/itm/Engine-Oil-Pres ... 12&vxp=mtr.
I paid about 18€ for it in that time, so I guess a good investment.
My 5Bar VDO gauge gave a good similar reading as the mechanical gauge.
Bought sender at a VW beetle store at a very low price. Seems they are the same + also right threat.

[Big Jim]

Update .
I have got a 5 bar gauge from LB . The replacement gauge was reading off the scale when cold .After cleaning the connection on the sender it now reads 5 when cold . When hot it is 2 1/2 - 3 at idle and 4 1/2 when pushed . What do others do ?

Jim

[Lotus-e-Clan]

Update .
I have got a 5 bar gauge from LB . The replacement gauge was reading off the scale when cold .After cleaning the connection on the sender it now reads 5 when cold . When hot it is 2 1/2 - 3 at idle and 4 1/2 when pushed . What do others do ?

Jim

Sounds Ok.

Mines similar but a bit higher on idle when hot because I use 10/60 Castrol synthetic.

What oil do you use?

[Big Jim]

Valvoline 20 50 . The oil level was at midway in the dip stick when testing , so I guess the pressure would be higher when 'Full' ?

[Lotus-e-Clan]

No the pressure would be the same.

The level in the sump will not affect pressure unless you corner hard allowing air into the pick-up tube.... you then will be in trouble cos the pressure will drop mahusively for a moment and the bearing shells will pick-up...especially on the big ends....and then your oil pressure will be permanently low!

Best not to run with low oil at all - best check and top-up after each trip (especially a long one) or at least weekly.

If you are using a lot of oil (less than 1000 miles per litre) then try Castrol 10/60 it's thicker when hot so less gets past the piston rings. You won't get low modern oil consumption (10,000 miles per litre) from the 900 series engine even when new but 3000 mile per litre should be possible depending on driving style etc.

[Red1]

Hi all,

After my camshaftgasket disaster i am now running Castrol 10W-60 also and the oil consumption is now very acceptable. Runs just as nice to my ears, but after a long damped 500 km drive the back turns slightly black, like a real old fashioned sports car