Oil pressure testing for dummies

[maxsaudi]

The red oil pressure light came on a few blocks from our house, we limped the car home and is has been parked since Sunday when it happened. I have read several threads about it on here but I would really appreciate it if someone could walk me through the steps of how to test the pressure, what rpms/temps to do it at and what the normal readings should be. We picked up a test gauge at harbor freight with the 10x1 fitting so hopefully that will work. I'm desperately hoping it's the pressure switch and not something more. Thanks in advance

[ADCS]

Well the first thing is what oil do you use and have you checked the oil level since the light came on? Check with a cold engine first to make sure it is not empty. It would be good to also check it at hot (engine just turned off) and warm (engine off for 10-15 mins). If there is a big variance that can point you to sludge problems. Before this incident were you in the habit of periodically checking your oil level? Do you burn oil? Do you ever have to top up between changes?

[ADCS]

And check out this thread of you haven't already seen it
http://www.audizine.com/forum/showth...-warning-light

[maxsaudi]

Yes, it does lose some oil between changes. Shop says it needs new oil pan gasket and head gasket. Oil was changed 6-8 weeks ago and synthetic is always used. It seems to be using oil up that way vs burning it.

[PreciseD]

What was the shops reasoning for the need of a new head gasket? Do you have oil in your coolant? Coolant in your oil?

[SlickFix]

Hopefully, some kind soul with a Bentley manual on DVD will paste the instructions in here. My manual is hard cover.

[Dubsport Inc]

Sounds like your valve cover gasket and cam chain adjuster gaskets are gone and not head/oil pan gaskets!

[ECS Tuning-Audi]

Checking the oil pressure is pretty easy.

The best way to do it is remove the pressure switch and thread in the gauge. I forget off hand what the oil pressure values should read but if you search you should be able to find them.

If you aren't getting the right pressure when you first start and begin to rev it chances are it's not going to improve so the sooner you can shut it down the better to reduce risks of any damage.

Anyone have the oil pressure switch socket size off hand? I can't recall that either. It's pretty large. Maybe like 19mm or 21mm?

Jason

[PreciseD]

Cold Idle: ~80 psi
Cold 2k rpms: ~90 psi
Cold 3k rpms: ~100psi (pegs the gauge)
Hot Idle: ~24 psi
Hot 2k rpms: ~50 psi
Hot 3k rpms: ~70 psi
Hot at redline can still peg the gauge (100 psi)

[akaEsCo01]

Get an accurate oil pressure gauge first, I read the harbor freight ones are not all that great. I buy a good amount of their tools, but anything that needs precision and accuracy I will buy quality.

Second, the test is really simple. Take out the oil pressure switch connected to the oil filter housing and screw in the gauge. The hose on a quality tool will be long enough for you to lay it on your windshield right in front of your driver's seat so you can see it. Don't test it with a cold engine because that will tell you absolutely nothing. Your oil pressure is extra high at startup and even after the engine is just warmed up hence why a car will low oil pressure can drive for 15-20 minutes before the light will actually come on. Since you are reading it at the same place where the pressure switch would ping the light on the dash then you need to treat it the same way with the oil pressure gauge. Hold the throttle at between 2K and 5K and record your results. I don't remember off the top of my head, but you should see 2 bar at 2K.

Possible causes for low oil pressure are as simple as a clogged pickup tube, a little more involved would be an oil pump, bad piston rings, or sludge. Take a good inspection of your pan and oil quality if you have to take it off. Things like a leaky valve cover or cam chain adjuster gasket will not cause low oil pressure. If you had low enough oil pressure they wouldn't be seeing that much oil considering oil goes from the bottom up.

Good luck

[ECS Tuning-Audi]

Don't test it with a cold engine because that will tell you absolutely nothing.

Sorry but I do not agree with this at all. There could be a chance that his pick up is pretty clogged or the pump has failed. Yes the oil pressure light has specific values it needs to see before it trips the light, but if you are not getting oil to important places and you keep running the engine you will cause more harm than good.

Hook the gauge up, if your pressure is below what the cold engine idle value should be at its lowest then shut the car off. That will immediately tell you that you have a pressure issue and either the pick up is clogged or the pump has failed. Do not wait for the vehicle to warm up to see if it improves.

It doesn't take long to cause serious damage to an engine that isn't properly oiled.

Jason

[maxsaudi]

I was wrong, it is valve cover gaskets, not head gasket. Blame the lack of coffee.

[maxsaudi]

Holy crap, I'm finding it pretty much impossible to hook up the gauge to the test port. I think you have to be gumby to do it.

[maxsaudi]

80,90,100psi respectively when cold
30 at op temp idle
65@2k
75@3k
95@5k

Does this mean it's the switch?

[walky_talky20]

Those values look great. 95psi at 5k when hot is fantastic and indicates that everything is flowing very well. (when it starts to clog you lose the high-rev hot pressure first).

At this point, you could test the switch output if you like. Or you could just replace it. There is a chance it is the wiring or even the instrument cluster itself that is faulty, but the switch is most likely (assuming the wire and connector directly at the switch is in good condition - it's a hard life down there).

[maxsaudi]

Everything looked good until the bolt that goes in the test plug stripped out. I think our only option now is to tow it in and have that whole unit replaced. Not a good ending to the day.