Question about oil pressure unit?

[kibs45]

I have a 82 Audi 1.6 NA, and my oil pressure light lights up and buzzes me everytime the car revs up (roughly 2k-2.5k, every gear, warm and cold absolutely no light at idle), I have checked the Bentley and they say it is a faulty switch, bad "control unit", or no alternator signal.  The car has only done this for a couple of days.  Any other thoughts from anyone who has seen this before?

[Turbinepowered]

My strongest inclination would be to say that your oil filter mounted pressure switch is bad, but start checking the cheapest and easiest thing first. Make sure the thin wire at your alternator's "W" terminal has clean contacts and is firmly attached.

If that's good, then move on to the switches. They're cheap, just replace both of them. The one on the cylinder head is the low pressure switch, the one on the mount high pressure. Above X rpm (and apparently each Bentley gives a different value here :roll:) the system starts looking at the status of the high pressure switch. Below that value, it's looking at the low pressure switch.

Your symptoms are consistent with either a high pressure switch failure or an oil pressure problem. I'll keep my fingers crossed that it's the switch.

[Vincent Waldon]

Audi diesels share VW's "dynamic oil pressure warning system" which has two sensors:

1) a sensitive sensor mounted to the drivers side of the head.  The warning system monitors this sensor continuously and if it detects a problem the oil pressure light will flash

2) a not-so-sensitive sensor mounted on the oil filter flange.  The warning system monitors this sensor whenever the engine is over 2500 RPM and if it detects a problem the oil pressure the oil pressure light will flash and the buzzer will sound.  On a diesel engine the warning system figures out RPM based on the W signal from the alternator.

What the above means for you is that you have an issue with the high-pressure sensor system (because it's the buzzer) and the fact that only happens when you're over 2500 RPM suggests that the W signal is just fine.... the cluster seems to know how fast the engine is going.

If you google on this you'll find hundreds of threads scattered across the interweb:  the system is a bit complex, the sensors have a tendency to degrade, *and* these engines are in fact getting long in the tooth and starting to have oil pressure that's "on the edge" and so setting off the buzzer.

The interweb is also full of quick fixes: change to a thicker oil, get rid of that evil orange oil filter, just replace all your sensors, throw in a new oil pump.

As Turbinepowered and Libbybapa have suggested... we can be more scientific.  Because it's the buzzer we know it's the high-pressure side of the system.  Either the warning system is faulty or you really have low oil pressure.  If you have access to an oil pressure gauge (even a cheapie from Napa or Autozone works fine) I always suggest starting with "hows my oil pressure, really".  The Bentley will tell you the specs, and it's very comforting to know that your engine is healthy before spending a bunch of time trying to fix a warning system that in fact is only doing its job.

Assuming that your oil pressure is fine you can troubleshoot further:  the high pressure switch is normally open and closes at the appropriate pressure.  So, the troubleshooting bypass is to ground the wire going to the sensor mounted on the oil filter flange and then rev the engine above 2500.  If the buzzer stays off you can be pretty confident the switch is defective.  If the buzzer still comes on you either have a problem with the wire to the cluster or the cluster itself.

Clear as mud?! :wink:

[kibs45]

I really appreciate all this I have done some work with the 2.0 ABA and some other engines, so I am familiar with some VW stuff (and that the evil orange filter trips these sensors often) but this Bentley is not as concise as the one for my 1990 100q.  Originally when I purchased the car it indicated low oil pressure at idle, but it turned out the w terminal on the alternator was disconnected and after being reattached the light remained off completely.  A couple of days ago it started this, I use Fleetguard Filters (Cummins Engine Filtration), and Valvoline Premium Blue 15-40.  I know the engine has been running a little rich so I suppose the oil could have thinned.  I will hook up an actual guage to see but I will also look at Vincents suggestion.  The wealth of information here is fantastic.

[kibs45]

I guess when you are dealing with 26 yr old wiring it would behoove to make sure the connector didn't seperate from the wire...Thanks again.  By the way what are the two wires/sensors on the coolant/heater flange?

[kibs45]

I realize the mixture is a function of the pump (it needs a little work) but it is still getting 40-45 mpg so I can not complain too much.  However the broken wire did fix the problem.

[jtanguay]

worst case scenario would be a leaking injector... and that would cause the diesel to thin out your motor oil.  it is much worse in a gasser though because gasoline is probably on par with water in terms of lubrication.  diesel fuel has built in upper cylinder lubricant if you will  :lol: - another good reason to add a lubricity additive to your oil!!!

[92EcoDiesel Jetta]

Audi diesels share VW's "dynamic oil pressure warning system" which has two sensors:

1) a sensitive sensor mounted to the drivers side of the head.  The warning system monitors this sensor continuously and if it detects a problem the oil pressure light will flash

2) a not-so-sensitive sensor mounted on the oil filter flange.  The warning system monitors this sensor whenever the engine is over 2500 RPM and if it detects a problem the oil pressure the oil pressure light will flash and the buzzer will sound.  On a diesel engine the warning system figures out RPM based on the W signal from the alternator.

What the above means for you is that you have an issue with the high-pressure sensor system (because it's the buzzer) and the fact that only happens when you're over 2500 RPM suggests that the W signal is just fine.... the cluster seems to know how fast the engine is going.

If you google on this you'll find hundreds of threads scattered across the interweb:  the system is a bit complex, the sensors have a tendency to degrade, *and* these engines are in fact getting long in the tooth and starting to have oil pressure that's "on the edge" and so setting off the buzzer.

The interweb is also full of quick fixes: change to a thicker oil, get rid of that evil orange oil filter, just replace all your sensors, throw in a new oil pump.

As Turbinepowered and Libbybapa have suggested... we can be more scientific.  Because it's the buzzer we know it's the high-pressure side of the system.  Either the warning system is faulty or you really have low oil pressure.  If you have access to an oil pressure gauge (even a cheapie from Napa or Autozone works fine) I always suggest starting with "hows my oil pressure, really".  The Bentley will tell you the specs, and it's very comforting to know that your engine is healthy before spending a bunch of time trying to fix a warning system that in fact is only doing its job.

Assuming that your oil pressure is fine you can troubleshoot further:  the high pressure switch is normally open and closes at the appropriate pressure.  So, the troubleshooting bypass is to ground the wire going to the sensor mounted on the oil filter flange and then rev the engine above 2500.  If the buzzer stays off you can be pretty confident the switch is defective.  If the buzzer still comes on you either have a problem with the wire to the cluster or the cluster itself.

Clear as mud?! :wink:

I installed an oil pressure gauge at the oil filter flange first, then moved it to the cyl head. Pressure readings were pretty much the same at both locations: 8 psi at idle and 22 psi at 60 mph in 5th, engine fully warmed up. Sounds kinda low to me. I wonder if the Fram oil filter has something to do with the low oil pressure? Should I change the oil filter to a Purolator or Wix before investigating further?

[Vincent Waldon]

You're probably pulling 3000+ RPM on the highway and are supposed to have almost 30psi at 2000 RPM, so I'd say you're low.

You could try a different oil filter and it might buy you a bit of pressure... you could also switch to a heavier oil... 20W50 can make quite a difference if you've been running 10W30 for example.

The usual cause of low oil pressure, unfortunately, is bearing wear (mains/rods/IM shaft)... how many miles on this engine?  

If a filter and oil chance doesn't make any noticable difference the standard approach is to:

- pull the oil pan
- check the oil pump screen for obstructions
- pull the oil pump and follow the Bentley wear measurement procedure
- pull a main bearing cap or two and a rod bearing cap or two and Plastigauge them

Lastly, IM shaft bearings cost a lot of oil pressure when they wear... which the sprocket side one does in spades when the timing belt is over-tightened.  With some engine disassembly the front bearing can be physically examined with the engine in the car, but on a transverse chassis like a Jetta the engine pretty much has to come out to change the bearings... unless you don't mind adding some extra holes to the inside of the fender.

Having said all of that:  8 psi at hot idle and 22 psi on the go are probably reasonably safe... low, but your engine is certainly getting enough oil.  With a dash-mounted gauge you'll be able to tell if it ever gets worse.

One last thought... is that a really cheap gauge?  If so, know anyone that could lend you their gauge, for a second opinion?

[92EcoDiesel Jetta]

Vince, the odometer reads 180k. The oil pressure gauge is from a $30 3-gauge set from Autozone. I will check it against other gauges I have. I am hoping the gauge is off. If not, I will then check the items you listed. Are there 20W50 diesel rated oil?

[92EcoDiesel Jetta]

[quote author=92EcoDiesel Jetta link=topic=17907.msg155762#msg155762

I installed an oil pressure gauge at the oil filter flange first, then moved it to the cyl head. Pressure readings were pretty much the same at both locations: 8 psi at idle and 22 psi at 60 mph in 5th, engine fully warmed up. Sounds kinda low to me. I wonder if the Fram oil filter has something to do with the low oil pressure? Should I change the oil filter to a Purolator or Wix before investigating further?
[/quote]

I calibrated my cheapo oil pressure gauge to a Mercedes 300D oil pressure gauge. My gauge was reading low. I calibrated it by twisting the Bourdon tube a little by reaching in the light bulb hole with long nose pliers. After calibration, at idle I am now reading 20 psi and at 60 in 5th I am reading 35 psi. I am going to plumb in the Mercedes oil pressure gauge temporarily to double check that I calibrated the cheapo gauge "good enough".