Oil Pressure again

quattro

quattro

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On start up, Sparky's bloo..... Oil pressure sits at just above 30 PSI for a few seconds, then can drop to between 5 and 15 :shock: A gentle dip on the throttle to slowly increase the revs makes it drop even more and then it increases when the I let go of the throttle. Yesterday it actually dropped to zero.

As soon as I start driving (e.g. get out of traffic and onto the motorway) it goes back to normal, i.e. 45-50 at 2,000 rpm and just over 30 at tickover, but can (if sitting in traffic) drop to very low figures again.

The oil light doesn't come on, but does work with just the ignition is on.

It doesn't make any noise at 0 - 5 PSI so I am thinking it could be the gauge, or associated wiring. Fuel gauge and temperature work perfectly.

I will be checking the tightness of the gauge wiring tonight, any other ideas?

Richard
 
Hmmm, it is worrying watching the needle fall away to zero, but I'd be inclined to think it's an electrical problem triggered by temperature/pressure change.
 
I agree with Paul that an electrical malady is the most likely - what about the guage working loose on the circuit board? Or perhaps the volyage stabiliser loose on the board - any other gauges misbehaving in sympathy?

I've been trying to think of any mechanical maladies that could produce effects like that. Perhaps the most likely is a sticky pressure relief valve (ribbed ball perhaps?). Otherwise you're looking for something loose that either opens a big hole early in the oil supply system, or prevents the pump picking up (but I'd have thaought that might have been accompanied by pump scream?).

Chris
 
Cheers lads.

Things buzzing through my head are from, loose connection on the sender, right up to loose pick up pipe in the sump ( I did take that off not so long ago, so did I tighten it up properly? :shock: )

I'll pull the wire off the sender tonight, give it a clean and crimp it up a bit. Hopefully that will solve it.

What is confusing though, is why does the pressure drop as the revs increase?

Richard
 
Richard.

Years ago i came across this exact problem - oil pressure was down a bit on idle, and when the engine was revved, the pressure dropped away. (usually when the engine was cold and the oil thick).
This was traced to a faulty O ring on the pick up pipe assembly. I suspect that it sort of held it's pressure in balance with the dodgy o ring, and then when the oil pump needed more suction, the O ring deformed, thus sucking in air and reducing the oil pressure.
First off, i would check all electrical connections, then connect a separate oil gauge up to confirm, before going into the engine.

Hopefully it will be something simple, and you get it sorted quickly.
Glen.
 
chrisyork said:
what about the guage working loose on the circuit board?
Click to expand...


That would be my next check. I had oil pressure guage problems a while back with the guage working intermittently. The guage is fed by contact pressure only on the circuit board so a good clean of the contacts might help.

Hope so :?

Dave
 
First port of call is a mechanical oil pressure gauge check. Low oil pressure is a concern for long term driving however you can drive around with less than 5 psi with little damage for a short while, I once drove my car (Ford 3.0 litre V6) for several thousand miles with the oil light on and the oil pressure was 5 psi or less, just used thicker grades of oil to alay my conscience> When that engine died it was from other causes than the oil pressure.

Graeme
 
quattro said:
The oil light doesn't come on, but does work with just the ignition is on.

It doesn't make any noise at 0 - 5 PSI....

Richard
Click to expand...

I'd say it's a poor electrical contact somewhere Richard.

I had somewhat randomly low readings develop intermittently soon after I did Occie's top end, and wasn't happy until I'd fitted a Smith's mechanical gauge - which confirmed everything was OK.

I rarely bother looking at the original gauge now, but it still seems to have a mind of its own sometimes.

Good luck with it.
 
Mine sometimes drops gradually off when driving, I turn the engine off & restart, and it sometimes goes back to normal. I reckon its the pressure transmitter on mine.. I'll try the tapping it with a screwdriver trick to see what happens, but there are no untoward symptoms from the engine when it does this. Never drops to a dangerously low reading though.
 
The previous owner of my car (19 yrs ago) freaked and commenced an engine-out rebuild when the oil gauge suddenly dropped to zero. After a botched motor overhaul it turned out to be a bad connection on the sender........
 
I have cleaned up the connector on the gauge and tightened the spade, no difference.

I have changed the gauge for a spare one, no difference.

This is the worrying bit - click on video



Yet, 20 minutes later with a warm engine, its running properly.

100_2144a.jpg


I have connected a resistance meter across the gauge and at rest (Engine stopped) it reads 28.1. When ticking over it reads between 17 and 22. I now have to let the engine cool down to see what it does when revved cold. I am hoping that the resistance reduces as the revs rise, but we will see.

Richard
 
Hi Richard if you have the new type transmitter with the black plastic top , rather than the old type original then i really wouldn't trust it !
 
I thought that Stina - it's an old original.

I'll wait for it to get cold again - tomorrow, then test it with the resistance meter.

If that shows it to be the gauge, or actually the oil pressure, then it's out with the mechanical gauge and get my hands dirty. :(

I'm hoping it just goes away LOL

Richard
 
From what i've read doesn't the light start to flicker at 8psi ?? If you've seen readings lover than 8psi and no light then i would put my money on an electrical gremlin :D
 
Even if the relief valve is sticking open with the engine cold, it wouldn't do it like this.
Worn engines and / or pumps show notoriously low oil pressure at hot idle, not cold revving.
I guess that leaves only a temperamental sender unit.
See what a capillary gauge says for peace of mind.
 
I don't trust the gauge sender unit, but do I trust the warning light sender?

I have a capillary gauge on the way, so we'll see what happens with that.

The previous owner spent over £6.5K on the engine, so I am a little nervous about ignoring this :shock:

Better hurry though, only three weeks to Beamish :D

Richard
 
Just a thought (but more than likely totally wrong though!)

On our old Vauxhall (the car didn't have an oil pressure gauge, but I'm wondering if what basically happened to us may be happening to you), the oil-pressure light switch sprung a leak; it was spitting out oil from the gap/clearance between the actual male lucar/spade connection and the switch body.

My wonder is what you're actually experiencing is due to oil somehow (compromised seal/rubber membrane?) finding it's way onto the actual resistance wire of the sender, which of course raises the resistance between the contact, so shows less movement on the pressure gauge.
 
Must admit, it does look like a transmitter problem, but it is weird how it drops off when you rev it, and comes back up at idle... :shock:
 
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