[mstein]

I was driving on the highway this weekend and felt an odd wobbling in the car. I had been driving for about 15 miles at the time. Minutes later the oil pressure warning with a STOP CAR on the screen came on. I opened the hood and there was some light smoke coming from the passenger side of the engine, maybe oil dripping on the cat? Anyway, I checked the oil level and it was below threshold. Luckily, I had some oil in the trunk and filled it up. The wobbling was also gone and I drove around 20 miles. The warning didn't come again that day.

Next day, I go grocery shopping and on the way home, after just 3 miles of driving, the oil pressure warning comes on again. This time without any wobbling or smoke from the car. I check the oil level and it's still filled up all the way. I was just one mile from home so I decided to go for it and drove the car home, praying I wouldn't break anything.

Today I took a look at the car: The oil level is still all the way up, so there is no major leak. The oil looks a bit dark, but not terrible I guess. It has been changed about one year ago (~5000 miles). Previous owner told me he always used synthetic oil and so have I since I bought the car 4 years ago.

The oil filler cap looks okay, so I guess there is no oil sludge issue?

I noticed the oil pressure sensor is covered in oil but so is almost everything in my engine room, I have never cleaned it and it was there since I got the car. I also saw that the wire shielding is retracted from the adapter. Could the sensor or the wiring be the problem or do you suspect something more sinister?

I am thinking of doing the following:
I want to install an oil pressure gauge following 2001.5 AWM Autometer Oil Pressure Gauge Install and Installing an Oil Pressure Gauge
If the oil pressure is fine, I will probably have to switch out the sensor, if not, I wouldn't know what to do next.

Instead of installing an oil pressure gauage, I also read somewhere that I could just run the engine for a bit or drive around for ~10 miles and then check whether I have oil coming up under the oil filler cap.

Any opinions or advice? As always, thanks a lot for helping a car noob as me.

 

[mstein]

Sorry, forgot to mention this: The car is a 2002 Volkswagen Passat B5 1.8T AWM. It has 116k miles.
No engine codes but a P0420 (cat running at low efficiency) which comes on and off periodically for years already.

 

[PZ]

Wobbling and oil pressure are not related. You will not see sludge at the cap. The real issue is coked oil that resembles sand and that plugs the oil pickup screen.
Does the light come on at idle? If so, the switch or wiring is bad.

I would start with a mechanical pressure tester. Be sure to run the car until the engine is hot, then run it at 3K rpm for 10-15minutes or until the pressure starts to drop. Report pressure when cold, hot idle, and at the 3K after 15minutes (or end of test).

 

[mstein]

Thanks, that's already helpful. I feared the wobbling could be friction induced.

I have been cautious about running the engine at all, fearing I'd break something. Running it at idle or at 3k RPM for 10-15 minutes won't hurt much? Do you mean standing or should I be driving for 10-15 minutes?

 

[AndreasPassat]

Wobbling and oil pressure are not related. You will not see sludge at the cap. The real issue is coked oil that resembles sand and that plugs the oil pickup screen.
Does the light come on at idle? If so, the switch or wiring is bad.

I would start with a mechanical pressure tester. Be sure to run the car until the engine is hot, then run it at 3K rpm for 10-15minutes or until the pressure starts to drop. Report pressure when cold, hot idle, and at the 3K after 15minutes (or end of test).

^^^ This ^^^

FYI
Oil pressure switches are known to sometimes fail. Cheap aftermarket switches tend leak through where the plastic is crimped into the threaded metal portion.
Also, make sure the pressure switch is snuggly seated. If it's not tight it won't make a good solid electrical connection causing erratic behavior. Ask me how I know about that...

 

[mstein]

Quick update:

• Oil light or STOP ENGINE warning doesn't come on at idle or even after driving for 10-15 minutes (didn't dare to drive any longer)
• The electrical harness connecting to the oil pressure sensor was full of oil (see picture below)
  • It was difficult to get the harness off because I couldn't get my hands into that tight space, so here is what I did if someone finds it helpful: I fed a long flathead screwdriver through the intake manifold from the top to push on the release tab. At the same time I used a pair of flat pliers to get the harness off. I found that it was much easier to push/lever the harness out rather than pulling it.
• I bought a mechanical oil pressure gauge, but I stripped the Allen head from the additional port on the oil cooler, so I won't be able to measure oil pressure through that. The Oil Pressure Relocation Kit from 42 Draft Designs seems to be no longer available and out of stock everywhere, so I cannot measure through the sensor's port either, at least not permanently.

^Oil in electrical harness of oil pressure sensor

So I have two questions now:

1. Can I measure oil pressure through the sensor's port using the mechanical oil pressure gauge? Are the threads also M10x1 on that port?
2. Would it be reasonable to assume the oil pressure sensor caused the problem, because there is oil leaking through?

 

[PZ]

The sensor should also be M10x1, so you can use that port. If the gauge was failing due to the oil, the light should be on all of the time. If sludge is the issue, it may take a while of highway driving for the pump screen to get clogged and the pressure to drop. I know on the motor I repaired, it was over 15 minutes of 80mph before the light came on.

 

[mstein]

Thanks @PZ, the M10x1 adapter fit well into the oil pressure sensor port. I measured the oil pressure wit the mechanical pressure gauge over time at idle and up to 3000rpm. I went back and forth between idling the car, going up to 2000rpm, up to 3000rpm and back to idle, always taking note of the oil pressure shown on the gauge.

It looks like the pressure goes slightly down over time and drops slightly below the limits that I found in the following posts. What do you guys make of this?

A double check on the big blue Bentley book pages B 17-5 [AEB ATW], and C17-4 [AUG, AWM] says oil pressure at idle min. 29psi, and range of 43-65psi @ 2000rpm 176F.

The VW technical site your article references http://volkswagen.msk.ru is wicked cool. The lubrication system section it provides for the ATW AEB Volkswagen 1,8L Engines AEB, ATW Lubrication system -aeb_atw_lubr_syst.pdf matches the Bentley pressure data above, while the data it presents for the AUG, AWM http://volkswagen.msk.ru/engine/aug_awm/aug_awm_engines.pdf directs Check oil pressure with engine at normal operating temperature. Oil pressure at idle should be not less than 1.3 bar (18.9 psi ). Oil pressure at 2000 RPM should be 3.5-4.5 bar(50.8-65.3 psi).

Go figure.

 

[PZ]

I would be content with 20psi at hot idle, I would run the test at 3K for 15 minutes to make sure it doesn't drop suddenly. Letting it idle can cause any coked oil/sludge/debris to drop away from the pickup screen and invalidate the test.
If the test is good, I would change the switch and clean the wiring harness. Then change the oil and filter, and use a 5W40 weight oil.

 

[mstein]

I changed the switch, cleaned the harness, changed oil and oil filter and used a 5W40 oil as you recommended. The light hasn't come back on since despite driving quite a bit. I went back to my notes and noticed I had actually driven almost 10k miles with the old oil.

I know I probably should have run the test with the mechanical gauge first but I figured the new switch would probably complain if something was still wrong with the oil pressure.