So here's my oil pressure problem..

[Vee-ard]

I need help.

I've got a Speco 2" electrical (not mechanical) oil pressure gauge installed in my car. Its hooked up to a "T" piece that has the factory oil pressure switch connected to the other side. (keep in mind its a 5.0L).

Lately I've been getting some ridiculously low oil pressure readings. The car has only just passed 80,000kms, (I've owned it since 56,000kms and pretty much put the gauge on straight away) On cold start up, it idles at about 40PSI, which isnt too bad, but when i first installed it, it used to idle at about 50PSI. but this isnt really what worries me. When the car heats up and I've been driving for about 15kms or more, it idles at 0(!) PSI (according to the gauge) when before it used to idle about 20-25PSI hot. Also, cruising down the freeway, it sits anywhere between 5-20PSI when before I used to get 30-40PSI at 100km/h.

I know 5.0L's idle oil pressure is really low, but looking at the gauge sit on 0 scares me, especially when it never used to. also, I dont like the idea of cruising at 100km/h and only getting 10PSI.

Occasionally the needle flickers from a low reading to about 20 PSI higher than whatever its reading, but then drops quickly. There's no rattling from the engine to indicate critically low oil pressure, and the factory oil pressure light isnt on. I've always changed the oil every 5000kms, sometimes less.

Things I've done to try fix this:
1) replaced the sender unit. (got exactly the same readings)
2) oil change with thicker oil (20w-60 penrite instead of 15w-60 penrite) and
3) replaced filter with brand new repco filter (TWICE).
4) taken sender off, checked for leaks, tightened.

I've also developed a steady leak from around the part of the block that sticks out where the oil filter mounts to. Not exactly sure where its coming from, but it ends up dripping where the oil filter gasket meets the mount. I now have a nice oil stain in my driveway. (it isnt the gasket leaking though). Is there some sort of valve or bolt around there that's bleeding all my pressure? or is there air stuck in the sender unit or something? do you have to prime the senders with oil?

The only thing I can think of that I may have done is used engine oil flush with my oil change and it seemed to happen around then. Have I ruined my compression or something by washing the sludge away or has the washed sludge blocked the pickup?

Im hoping someone can help me with this as its doing my head in, and I just want to be sure there's nothing actually wrong with the oil pump or lifters to cause the low oil pressure (if it is even low at all).

[Brett_jjj]

If the oil pressure shows a good high reading when the engine is cold,but drops off considerably once the engine is up to operating temperature, its usually a sign that the big end bearings and/or main crankshaft bearings are worn and need replacing.You should get a bit of a pressure drop once the engine warms up ,but not a significant one.Id be getting a different high quality oil pressure gauge connected to the engine to check its hot and cold oil pressures.This should be fairly cheap to get done at any mechanics.If it confirms the higher oil pressure when cold, and heaps low pressure once up at operating temperature,then go from there.It might be something else,but I think you will find its gonna be worn bearings.

[WogBoyz]

This prob isnt related however id use a Holden oil filter man, i used to use repco, The holden one is a fair bit bigger and looks much better quality inside then the repco one, i used to have some tapping noise since using the bigger Holden one noise gone, hopefully this helps in someway lol

[Vee-ard]

Worn big end bearings and/or crankshaft bearings at 80000kms? I hope not..

anyway, got a mechanic coming around wednesday to pressure test the oil system and we'll go from there.

from what I recently learnt though, my money is on a blocked pickup...

[Brett_jjj]

Mate, Ive seen bearings wear out in 20,000 km.Ive seen heaps of so-called rebuilt or reconditioned engines wear their main and conrod bearings out quickly because the oil galleries in the block were never cleaned out properly when the block was cleaned before assembly.This allows the dirt and grit left in the oil galleries to get in under the bearings and wear them out fairly quickly.Unless you did all of the cleaning ,machining and the reassembling of the the engine yourself,theres no way of knowing how clean things were when it was assembled,You say you change the engine oil every 5000ks.I cant see how the oil pickup could be blocked unless you use some really cheap bodgey oil in it, or use engine oil additives.The engine sump should be as clean as with regular oil changes like that.Ive only seen blocked oil pickups on engines where oil changes and servicing have never been done. The oil pressure test will show up whats wrong though.If the oil pressure on the mechanics gauge shows the same pressure drop once the engine is at operating temp,then Id say theres a 90 % chance its gonna be worn bearings.High oil pressure when cold,but low oil pressure once up at operating temp is a classic sign of worn main and/or big end bearings.

[Vee-ard]

quick update: mechanic came round, we put a mechanical oil pressure gauge on there - fine, idles at 15-20PSI, 40PSI at 2000rpm, 55-60PSI at 3500 RPM.

Gauge still shows idle at around 5PSI, 30 PSI at 2000 and 50 PSI at 3500. So i changed the gauge to a new one, still does it, although the needle doesnt flicker anymore.

New sender, new gauge, checked wire earth, motor is fine...? what next? tracing the wires and looking for a break that expands as it heats up and makes a false reading?

surely SPECO gauges are better than 15PSI off the real reading?

[hako]

Did the mechanic plug his gauge into the same hole your Speco one goes into?.....also what was your oil pressure warning light doing when the Speco indicated 0 psi?

[delcowizzid]

is the speco oil sender 1 wire if it is try run the gauge earth to the engine if 2 wire run it to the engine as well as the sender earth

[Vee-ard]

Did the mechanic plug his gauge into the same hole your Speco one goes into?.....also what was your oil pressure warning light doing when the Speco indicated 0 psi?

Hako: the factory pressure switch and the sender "bulb" are on a double adaptor "T-piece" where in a normal car just the factory pressure switch would sit. The mechanic unscrewed the factory oil pressure switch and plugged his mechanical one in there while the sender was still connected so we could compare pressures. He was getting a 15-20PSI idle while I was getting 5ish. Because there was no pressure switch plugged in the light wasnt doing anything, however when im driving the oil light has never come on once.

Delco: not sure what you mean? you've got the sender bulb where one wire comes off and leads to the signal connector on the gauge, then you've got an earth wire between the earth connector on the gauge and the car body then a power line to the accessories line. If you earth the signal wire before it reaches the gauge the gauge shoots up to maximum reading.

[delcowizzid]

earth the gauge negative onto the engine block instead of the body and see what the reading does youll find it most likely jumps higher all my gauges get wired with there earths to the block to stop ground offsets effecting readings they should allways be earthed to engine

[Not_An_Abba_Fan]

Have you tried plugging the guage's sender directly into the hole without the T piece? See what it does that way.

[Vee-ard]

earth the gauge negative onto the engine block instead of the body and see what the reading does youll find it most likely jumps higher all my gauges get wired with there earths to the block to stop ground offsets effecting readings they should allways be earthed to engine

thanks delco, ill try this when i get some free time.

abba: dont know why your idea didnt occur to me sooner.

I still want to keep the T piece, but that would be a good way to test the setup.

[Brett_jjj]

Good to hear it was just a faulty oil gauge or its connections and not an actual problem with the engine. At least you now know the engines true oil pressure readings.