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Wed Jul 03, 2019 12:02 pm

Hey all,
I've come to find VDO oil pressure/temp/idiot light instructions to be contradictory and confusing...
I installed my pressure gauge according to VDO instructions that it came with however upon turning the motor over 5-6 times it registers 0 psi - gauge doesn't budge.
I know the motor runs and puts out appropriate oil pressure, I just can't seem to troubleshoot the gauges functionality.

- I used a test light on the + terminal on the gauge which receives 12v from fuse panel - Light illuminates

- I thought that power would have gone through the gauge all the way back to the sender but if I touch the test light to the "S" terminal on the gauge, no power is there... test light stays dark and of course, there is no power at the sender... "S" terminal from gauge is connected to "G" post on the VDO dual post pressure sender...

- Oil light hooked up to the other terminal post "WK" on sender

Feeling kind of lost here as everything is connected as per the VDO instructions I received for standard ground, single pole however I have a dual post sender and these instructions I found on the VDO site are for a floating ground, show a dual pole sender yet neither show how to set up for use of both pressure to gauge and idiot light - they just read sender (temperature or pressure...

When using both pressure and idiot light do you use a floating ground and connect both rings to one terminal and the other to a ground? I thought the engine was ground...... AAAARGH!!!

Image is instruction I found on the VDO site, the retailer that sold me the gauge also sold me the dual post sender but only sent me the left side instructions for a standard ground.

Thanks for any insight/perspective you can lend.
Sorry for the confusion.

Wed Jul 03, 2019 12:12 pm

1302Paul wrote: I used a test light on the + terminal on the gauge which receives 12v from fuse panel - Light illuminates

- I thought that power would have gone through the gauge all the way back to the sender but if I touch the test light to the "S" terminal on the gauge, no power is there... test light stays dark and of course, there is no power at the sender... "S" terminal from gauge is connected to "G" post on the VDO dual post pressure sender...

- Oil light hooked up to the other terminal post "WK" on sender

Wed Jul 03, 2019 2:07 pm

Thanks for the diagram.
This confirms that I have everything going to the right place, so I can't be too far off...

A quick question on the gauge functionality itself.
Is it supposed to transfer power from the + terminal through G terminal (S on my gauge) directly to the pressure sensor?

Wed Jul 03, 2019 2:26 pm

The WK post on the sending unit supports the OIL warning lamp in the speedo. This WK post is an ON/OFF switch to ground thru the sending unit. With the engine OFF (no oil pressure) the WK post should be grounded. If you have your OIL lamp properly wired, it should be grounding thru the WK terminal to the engine case. Does your OIL lamp turn ON when you turn the ignition key to the ON/RUN position (engine NOT running)? Alternatively, measure the resistance from WK to the case. You should read zero ohms.
Get this working first because it will prove the sending unit is grounding to the case. If the WK is not grounding it is doubtful you will get the G terminal to work.

The G terminal is a variable resistance to ground. This is how the gauge judges how much pressure there is in the oil system. I believe the resistance increases as oil pressure increases. I was testing a friend's VDO gauge last week and this is what we saw. I don't know if you should expect to get a voltage reading from the G terminal on the gauge. Was this listed as a legitimate test from VDO??

Also, it sounds like you are expecting the oil pump to build enough pressure by just cranking the engine? Does your engine not start and run?
We changed the oil in my friend's Beetle this past weekend. After putting 2.5qts back in we started the engine. It took around 20sec of the engine idling before we saw the OIL light go out and pressure start to register on his VDO gauge.
If your engine has not been running for a long time, I don't know if you should expect to see any pressure readings while just cranking the engine using the starter. Again you can confirm this with the OIL lamp. During the 5-6 times you cranked the engine did the OIL lamp ever go out? The OIL pressure switch is set to 7psi. That may not be enough to register on the pressure gauge so expect the gauge to take a sec or two longer than the lamp.

Wed Jul 03, 2019 3:44 pm

@ashman40

THank you for the insight.
I'm on the west coast so once I am home I will run these tests and get back to you later tonight.
As for the motor it is a brand new build and has been run and dyno'd so I know it runs out right and the builder says the pressure sender was reading right while it was running.
My trepidation in starting it was simply because i installed the oil cooler for the full flow system and thought I might be able to get some pressure by turning it over while getting the oil throughout the system. It's all topped up now.

For the oil light, I used the same wire that was used for the previous motors pressure switch however I'll double check the oil light for on/off tonight.

Wed Jul 03, 2019 9:49 pm

@ashman40

My OIL lamp turns ON when I turn the ignition key to the ON/RUN position and cranking it over for another 7-8 times the light doesn't go out, sounds as though I just need to confirm the full flow is flowing, connect the fuel pump and get things started...

Will follow up once I get it started and can see what the gauge is doing.
Thanks for you direction!

Thu Jul 04, 2019 2:06 am

Did you install the full flow system after you got the engine back from the builder? If so what did you add, filter, cooler or both? If you did any changes did you drain the engine oil? If you added a filter, take it off and see if it's full of oil, if not fill it. If you drained the engine, the pump may have lost it's prime as well.

Thu Jul 04, 2019 5:26 am

Check oil pressure with a mechanical gauge or take the sending unit out and crank engine and watch for oil flowing . Try to catch it with a rag .

Thu Jul 04, 2019 11:41 am

@Multi69s
I installed the full flow after I got the motor and installed the 96 pass cooler with fan and filter - topped up filter before I installed it and back filled the cooler from the top down to the filter. I didn't drain the engine, just topped up the system, cranked it a few times let it sit and then checked the oil level on the dip stick, repeated until satisfied it was at the appropriate level.

@vwoldbug
I'm going to loosen the full flow connection, crank it and confirm flow.

Thanks for the help.