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  View original topic: VDO Oil Pressure Gage Acting Strange
KarmannMarco Sat Apr 03, 2010 7:39 pm

Hey guys. Since recently buyng my Ghia i figured a vital item to install is an oil pressure gauge. Well i bought a nice simple 80 PSI VDO gauge brand new. It has 3 hook ups in the back , power , ground and sender.
I bought a VDO oil pressure sending unit from a samba member with the following specs that looks exactly what VDO calls for.
9.96
30/2
0-5 bar
0,5 +/- .15 bar.

I know 0-5 bar is equal to 0-80 psi so i felt this was correct for my gauge.

Here's the issue... I wired it all up today. Sending unit went in the factory sending unit hole with no problems. Hooked up the wire to the G side of the sending unit (the other side "WK" is for the dummy light). Turned on the ignition and the gage came to life going straight to 80 psi. The i started the car and the pressure came down to about 75 psi. When i drive around the pressure fluctuates between 70 and 80 psi which i dont think is correct. The car runs great so i dont honestly think its a oil pressure issue because even after 10 minutes of driving the pressure does not lower......

Any ideas? Wrong gage? Wrong sending unit?

Cusser Sat Apr 03, 2010 9:25 pm

I've had VDO oil pressure gauge on mine since 1977. When I turn on the ignition without starting the VW, the pressure still reads zero. After warming the engine up, I get about 10 psi for each 1000 rpm.

My gauge also is wired into the dash lights. G is correct for the gauge, and WK goes to the idiot light in the dash. I'd make sure my ground wire was really installed to good ground.

GMFCO Sun Apr 04, 2010 5:13 pm

Interesting - I just installed my sender today. Inserted a t-fitting to use original warning sender.

Mine reads 0psi. When I hook it up the needle raises just above the lower limiting peg but not up to 0. If I disconnect the ground, it maxes out.

KarmannMarco Mon Apr 12, 2010 11:36 pm

Interestingly enough i tested my gauge again today. This time directly in the back where the engine is at. Grounded the ground very very well directly on the battery. Hooked up 12 volts to it and hooked up the signal wire from the VDO sending unit and with the engine running the gauge jumped to 80 psi.
What is the regular "warm" oil pressure for a 1500 sp?
Is it possible that the position of the sending unit (how far in or out its threaded into the block) may cause different reading?
Any ideas? What do the ?????? numbers mean?


9.96 --------??????
30/2 ------- Thread pitch
0-5 bar ------- PSI (0-80 in this case i believe)
0,5 +/- .15 bar.------- ????

cool karmann collected Tue Apr 13, 2010 4:49 am

Idle pressure when warm on a stock 1500 could be anywhere from 5psi to 15 psi depending on how healthy (or not) the engine is. Your problems sound electrical rather than mechanical (i.e depth of thread). The fact the gauge goes straight to 80psi suggests a dead short to ground on the sender wire, so either it's touching somewhere it shouldn't (maybe even the body of the sending unit) OR the sender itself is duff. Remember, the gauge needle jumps to 80psi even without starting the engine.

>are you sure the gauge is wired correctly? the fact that the pressure drops as the engine warms could mean the polarity to the gauge itself is reversed.

Unless someone jumps in first, I'll measure the resistance between the G terminal and the case when I get home and report back.

Ant

70 140 Tue Apr 13, 2010 5:08 am

I would guess the sender... but only because you bought it used and the gauge is new.

Is it the 2 prong sender that lets you keep the oil warning light?

gimpy60 Tue Apr 13, 2010 7:03 am

"G" terminal is for idiot light, "wk" goes to guage.

iradi Tue Apr 13, 2010 10:19 am

Check the connections.

http://www.egauges.com/pdf/vdo/0-515-012-123.pdf

KarmannMarco Tue Apr 13, 2010 10:23 am

yeah its the two prong sensor with G and WK . I have it wired up correctly with the G connector going to the Oil gauge.
Cool karmann collected , i went out there and made sure the sender was not grounding out in any way. Connected the wire directly to the gauge in the back so that i know for sure the wire going through the car to the front wasnt grounding out. Made sure all three connections were correct and very tight. Started the car and the gauge jumped to 80 psi , as it wormed up it gradually dropped fluctuating between 60 and 70 on idle. Very strange. Its almost as if the needle is strarting on the wrong side.....

How could the polarity to the gauge be reversed? Internally?

cool karmann collected Tue Apr 13, 2010 1:23 pm

er... I was thinking maybe externally if you know what I mean! :lol: Obviously you've checked the connections now so thats not it, sadly I realised I left my DVM at work so can't check cold resistance at the mo, but will do so tomorrow.

Actually I've just had a thought. I was talking rubbish earlier, if the gauge jumps to 80 psi (i.e maximum) that means either the sender is duff (again) OR there is a break in the wire to the sender somewhere.

Try this, connect the sender wire directly to ground somewhere (forget the sender for a moment) and turn on the ignition. Needle on gauge should stay at or near zero. If this is the case, the wire is OK but the sender is at fault, if it still jumps across to 80 psi then the wire is broken somewhere (do a continuity check to confirm) OR the gauge itself has a fault.

Hope you're not utterly confused yet.

Ant

gimpy60 Tue Apr 13, 2010 1:34 pm

I just bought one of these, they told me wrong way to hook it up. Glad I read this thread. :wink:

KarmannMarco Tue Apr 13, 2010 2:29 pm

cool karmann collected wrote: er... I was thinking maybe externally if you know what I mean! :lol: Obviously you've checked the connections now so thats not it, sadly I realised I left my DVM at work so can't check cold resistance at the mo, but will do so tomorrow.

Actually I've just had a thought. I was talking rubbish earlier, if the gauge jumps to 80 psi (i.e maximum) that means either the sender is duff (again) OR there is a break in the wire to the sender somewhere.

Try this, connect the sender wire directly to ground somewhere (forget the sender for a moment) and turn on the ignition. Needle on gauge should stay at or near zero. If this is the case, the wire is OK but the sender is at fault, if it still jumps across to 80 psi then the wire is broken somewhere (do a continuity check to confirm) OR the gauge itself has a fault.

Hope you're not utterly confused yet.

Ant

No , not confused. I used to be in the car audio business working on brand new cars so this isnt very complicated for me (at least the wiring part)
I will try this tonight. Thanks!

cool karmann collected Wed Apr 14, 2010 1:17 pm

Checked sender today, WK to ground was 3 ohms & G to ground was 10 ohms.

I take it you didn't use thread sealing tape on the sender when you installed it?

Ant

KarmannMarco Wed Apr 14, 2010 3:21 pm

cool karmann collected wrote: Checked sender today, WK to ground was 3 ohms & G to ground was 10 ohms.

I take it you didn't use thread sealing tape on the sender when you installed it?

Ant
Correct i did not. Literally screwed out the factory one and screwed in the VDO.
I will test my sender as soon as i get out of work.
Thanks! youve been real helpfull. I want to be 100% certain that its broken before asking the seller if he will take it back.

KarmannMarco Mon Apr 19, 2010 11:13 pm

Ok well , i remover my sender and did some measuring.
Got Infinity OHMS from the WK post to the body and 12 OHMS from the G post to the body.......seems like the sender i got is faulty....

Anyone have a 80 psi VDO oil pressure sender layng around for sale?? hehe

Nessal Thu Apr 22, 2010 8:41 am

Wow, I was just going to post my experience because I had the SAME PROBLEM. I also had a VDO oil pressure gauge and it worked fine for a few months. Then out of nowhere it would peg at 80PSI everytime I start the car. I thought it was a bad ground that might have caused this reading but then I rewired and made sure the ground was perfect. Still the problem persisted. I sent the sender unit in for a replacement and sure enough, it was the sender unit. Works perfectly after that.

KarmannMarco Thu Apr 22, 2010 10:30 am

It gets stranger and stranger....
So I have a 150 PSI old VDO oil pressure gauge layng around and figured for the heck of it i would wire it up and see what happened ..... this gauge says my oil pressure on idle is 10 psi and when the engine is revved it goes to about 20 psi.... i checked my oil and it is a little low so i will top off tomorrow and retest it....

Anyone know the approximate oil pressures and idle and at higher rpms for these engines? I have a 1500 sp.

Cusser Thu Apr 22, 2010 12:08 pm

KarmannMarco wrote:
Anyone know the approximate oil pressures and idle and at higher rpms for these engines? I have a 1500 sp.

When engine is warmed up:

20 psi at 2000rpm
30 psi at 3000rpm
40 psi at 4000 rpm

Of course, can depend upon your oil viscosity, straight-weight v. multi-grade...

My VDO sender has worked well for over 30 years.



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