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VanWagon
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Joined: April 12, 2022
Posts: 70
Location: USA
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 Posted: Fri May 06, 2022 6:30 am Post subject: Oil pressure sensor troubleshooting |
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After reading through dozens of posts, and thinking I've got a good grasp on how to manage My oil pressure sensor alarm going off, I wanted a second set of eyes. Using this post from a different thread as background, I listed what I did below...
| crazyvwvanman wrote: |
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The "high pressure" switch is supposed to be .9 bar, around 13 psi (some parts books and even some places in the Bentley wrongly say 1.8 bar, WRONG)
The "high pressure" switch goes by the water pump.
The "high pressure" switch must connect to a yellow wire in the main vehicle harness going to the dash and then pin 12 of the cluster 14 pin connector. (sometimes starts out green at the engine harness, then connects to yellow inside the engine compartment wiring box)
The low pressure switch is supposed to be .3 bar or close to that like .25 bar, around 4 psi.
The low pressure switch goes down by the pushrods on left side.
The low pressure switch must connect to a blue/black wire in the main vehicle harness.
The low pressure blue/black wire goes up to the dash and then pin 13 of the cluster 14 pin.
In about 5 minutes you can test the switches and wires with a test light or ohm meter.
If you are comfortable working with the cluster, start at that end.
Unplug the 14 pin connector from the cluster. Find the blue/black wire (not the blue)
Turn on the key but leave engine off.
Test the blue/black wire for the presence of GROUND
Start the engine, verify that ground is now GONE
Are both things are true? They must be for the oil warning to work properly.
Move on to the yellow wire.
With key on but engine off.
Test the yellow wire for the presence of GROUND, should NOT have it!
Start engine and slowly rev to 2500+, verify that the yellow wire NOW has GROUND
Are both things true? They must be for the cluster oil warning to work properly.
Of course the oil pressure changes as the oil gets hotter so the rpm needed to trigger the high pressure will also change. VW expects the high switch to trigger at 2000+ even with hot oil. With cold oil it can trigger at idle rpm.
Mark |
Troubleshooting a oil alarm.
Recently purchased 87 vanagon 2.1 l. Previous owner stated he had bypassed and annoying oil alarm after troubleshooting it with the shop and replacing all the "parts" that could legitimately be causing it. Unclear what he actually did.
2 weeks into ownership now. I've already fixed a few underline issues and basic repairs given it's age. This includes replacing fuel lines, resealed the gas tank, replaced missing idle control unit, replaced the blue foil on the cluster gauge, change the oil, filter, EVAP tanks in wheel well, fuel filter, spark plugs, distributor, spark plug wires, ran new windshield washer tubing, set timing @3k/35* and a few other things. I've tried to drive it between each part to confirm no new issues.
While going through the gauges, I noticed that the oil pressure buzzer pin was pushed over, therefore bypassing the buzzer. I bent it back into place, and installed a vanagon gauge cluster wire replacement. Now the buzzer is back in the system.
Also, during this I noticed that the oil pressure alarm light does not stay illuminated when the key is turned on. It never did. This the low pressure alarm was also not working.
Low pressure alarm:
Using the above method, and a multimeter, pin 13 on the gauge cluster wiring harness, the black and blue wire, does not complete a circuit when I turn the key on. When I start the car it still does not complete a circuit with a ground.
From my understanding, this means that there is a disconnection somewhere, either by a faulty sensor, broken wire, or disconnect further back in that circuit. Checked continuity of wiring and it appears good from dash to engine bay. Moving back...
Engine compartment:. Touching a test light between the positive alternator terminal and the black/blue wire as it enters the engine compartment, as part of a two-wire oil pressure sensor pair, the light is off when the key is in the on position, is off at idle, and off at greater than 2000 RPMs.
Looking into the circuit further back, I can see that the low pressure sensor is connected but the wire is old and brittle so I replaced it and soldered ends to the appropriate male female speed terminals. If I ground that wire to the engine, it allows the dash light to blink when the key is in the on position but not yet started. This does not happen when the wire is connected to the sensor.
Conclusion: low pressure sensor is bad. Everything before it in the circuit checks out.
High pressure system:
Engine compartment: touching a test light between the alternator positive, and yellow wire of the two pressure sensor wires, the test light does not illuminate while the key is in the on position, but does turn on with some occasional flashing at idle, and is definitely steady on above 2000 RPMs. I soldered up a new wire to replace the old brittle one. Going for a drive, and after about 10 minutes of driving, the dash alarm comes on and the light flashes. This happens when I'm 2 to 3,000 RPMs (4th gear), but if I downshift from fourth to third ( increasing the RPMs), it immediately goes away. Shifting back to forth at the same speed will cause the alarm to go off again within 30 seconds or so. This happens only after I've been driving for long enough to warm up the van, like 10 to 15 minutes or more. Oil level is appropriate on the dipstick. Current temperatures are between 50 and 70 Fahrenheit, and I used 10W40 oil, 5 quarts since I couldn't find 15W 50 or 15w40 on my oil change run to the store and I knew I would swap the oil after only a few hundred miles to do other improvements ( I just wanted to get his 2-year-old oil out of it, and this oil was recommended by some on this forum.
I don't want to turn this into an oil debate, but if you think this is a true cause of the alarm, let me know). The previous owner is a reputable person in a small town, and though it wasn't his daily driver, he did drive it every 1 to 2 weeks over the past couple of years. He told me when I purchased it that the local mechanics had replaced "all parts" that could have caused the low pressure alarm to go off, and ultimately they just decided to bypass it. So he was aware of the alarm going off and both him and his mechanic were no longer worried about it. I'm not going to accept that right away because of the potential implications if I'm wrong assuming it and I want to be able to take this on road trips for up to a thousand miles each way.
So here's my current thought...
There could be something wrong with the L-shaped board in the gauge cluster where the dynamic oil pressure wires come into the dash. It's always possible that is the issue, but before assuming it is completely in error, is my thought process on the above high and low oil pressure alarms flawed and anyway? What would you do next?
I just ordered up a sender relocation tubing to move it up top of the engine and allow easier access. I plan to add an oil pressure gauge and place the sender off the extra port.
I am ordering up new high and low pressure switches to replace the ones discussed above.
Thoughts? |
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dobryan
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Vana Guy
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Joined: August 23, 2016
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| Posted: Fri May 06, 2022 7:08 am Post subject: Re: Oil pressure sensor troubleshooting |
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The switches can be bad, or wrong values.
I had an alarm in a van I bought. Turned out the high pressure switch was 18 PSI, not the recommended 13 PSI (.9 bar for those still using the metric system). |
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ZsZ
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VanWagon
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Joined: April 12, 2022
Posts: 70
Location: USA
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| Posted: Fri May 06, 2022 8:58 pm Post subject: Re: Oil pressure sensor troubleshooting |
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Good info. I took it out again today, and it consistently does not buzz at 3000 RPMs. It will however buzz at 2000 to 2700.
I've got oil temp & pressure gauges on order, and new high and low pressure switches as well. I'm curious if it will fix the buzzer, but at least I'll have numbers to trend if it doesn't and I end up disabling the high pressure switch |
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VanWagon
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| Posted: Fri Jun 24, 2022 1:17 pm Post subject: Re: Oil pressure sensor troubleshooting |
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an update. OEM senders replaced. A Mansi relocation kit was installed which moved the low RPM oil pressure sensor from near the push rods below the engine to the top of the engine and adds a second port where I attached a sender for a new pressure/temp gauge as well. Here is what I found...
Startup pressures as measured from the top of the engine are appropriately elevated @ 60-80 while cold in 80F ambient temps.
Driving for an hour. Pressures drop to about 15-25 at cruising speed. 2500 rpm. When I come to an idle at camp (not in gear, not under load) the pressure gets into low single digits as (measured at the top of the engine). I had the low pressure light flicker as I bumped around camp trying to find a level spot (again measuring from the top of the engine), this may have been a bit front downhill. The low RPM low oil pressure light is new.
Temporary fixes I'm planning on doing to (hopefully) prolong things a little (and make me feel better about the numbers):
Thicker oil (20w50 planned).
Replace the pressure relief valve spring (I already have a replacement nut and oil temp sender I planned on installing there, so thought I would swap the spring while it was open.
Now my question:
From my (mis)understanding of physics, moving the sensor up higher on the engine creates a water column (or oil column in an engine) through that tube (unless we are measuring air pressure with direct communication between locations... so the numbers numbers measured at the top will read lower than the same sensor measuring at the bottom. Kind of how water pressures work when scuba diving. I know I am geeking out on this thought, and I could run a calculation to know exactly what this difference is based on a column of oil of given height and weight, but ultimately it is irrelevant because low numbers are low and even adding the difference created by moving a sensor up a water column will still make them lower than I want even if it lets me know what the true bottom of engine number is (which is where the OEM sensors read from). From my understanding, the numbers I get represent what are at the top of the engine (which is a worst case oil pressure anyway and therefore more important).
After overthinking this, my real question is...
Has anyone else had their low RPM low oil pressure sensor flicker after relocating it to the top of the engine? |
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DanHoug
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Joined: December 05, 2016
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Location: Bemidji, MN
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| Posted: Fri Jun 24, 2022 5:57 pm Post subject: Re: Oil pressure sensor troubleshooting |
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| VanWagon wrote: |
| Has anyone else had their low RPM low oil pressure sensor flicker after relocating it to the top of the engine? |
no. hydraulic pressure is the same at origin and end when there is no flow. if you're seeing 15psi at 2500rpm hot you have engine issues.
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-dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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BrownLoaf
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Location: Bellingham, WA
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| Posted: Sat Jun 25, 2022 7:02 am Post subject: Re: Oil pressure sensor troubleshooting |
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1 psi is equal to 27.7 inches of water column. Oil is less dense than water. By raising the pressure sender to the top of the engine, you can expect the measured pressure to be reduced by less than 1 psi. Not enough effect to be the cause of the low numbers you are seeing.
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87 Vanagon Syncro Tin Top WBX 2.1 "Bubbles" |
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VanWagon
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| Posted: Sat Jun 25, 2022 7:20 am Post subject: Re: Oil pressure sensor troubleshooting |
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| loganthecyclist wrote: |
| 1 psi is equal to 27.7 inches of water column. Oil is less dense than water. By raising the pressure sender to the top of the engine, you can expect the measured pressure to be reduced by less than 1 psi. Not enough effect to be the cause of the low numbers you are seeing. |
You are awesome. Thanks for answering my geeky question. I knew it caused some change, but I wasn't sure of the significance |
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hdenter
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| Posted: Sat Jun 25, 2022 7:41 am Post subject: Re: Oil pressure sensor troubleshooting |
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Aside from the mods you mentioned to raise pressure, you could install a higher volume oil pump. The reality, though, is that you will only be increasing the odds that this engine will grenade. Those kind of pressure numbers are usually caused by rod cap bolts starting to fail. First they stretch and loosen the caps and bearings which robs you of oil pressure, then they break and you get a new crank case ventilation hole. If you don't care about the core value of your engine because you have another or you are boxed in financially to drive this vehicle and you are praying that you'll find the money to replace/rebuild it before it blows, that's fine. But, if you need this core, you are just shooting craps in Vegas. Don't get me wrong, plenty of people have band-aided their motors and bought a little time. But some pay the price. You could think about doing a top end rebuild. Usually at this point the main bearings are still OK. Drop the motor, pull the heads and replace the rods without splitting the case. Check the end play once you have it on the ground. If that is still in the ballpark, go to town. With new rods and good main bearings you could get another 50k-100k out of this motor. Dave did a nice write-up on doing this with his current van. Good luck!
Hans
Hans
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hdenter
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| Posted: Sat Jun 25, 2022 7:46 am Post subject: Re: Oil pressure sensor troubleshooting |
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As for why you would now have a glowing light at idle, have you recently changed your oil and filter? Some of us have had problems with Bosch oil filters that are too restrictive. Stick with the Mann filters. There is thread about that whole issue somewhere...
Hans
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VanWagon
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| Posted: Sat Jun 25, 2022 9:03 am Post subject: Re: Oil pressure sensor troubleshooting |
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Great info in the last two replies. You also answered my next question. Any reason not to just continue until the engine craps out. I guess core value is significant enough to affect that decision.
I have a man filter in place, and since it was fresh a few hundred miles before, I did not swap the oil to change out the sensors, so I don't believe anything changed besides the sensor and its location. Location. It is getting warmer though, so maybe that has tipped it over the edge of lighting up the warning signal |
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