[Vwdiesel] Oil Pressure Warning System on '84 Rabbit

[Tony and Lillie]

For starters, the system works like this. On a traditional car, you have an 
oil pressure switch that switches at somewhere near 7-14 psi. That switch 
works the entire RPM range. This is a compromise, because it can't be too 
high, as it will be set off at idle. However, that is really too low at 
opperating RPM, and by the time the light comes on, there has been permenant 
damage to the engine.

VW had a better idea, which is the two sender system that is on your car. 
There is a low pressure sender that goes from idle to about 1800 RPM, and a 
high pressure sender that opperates above that. I don't know the pressure 
cutoffs for them, but I can explain the #'s you refer to for the senders. 
The low pressure should be around 14-25 psi. The higher pressure one goes up 
from there. The higher pressure one is the 2.1 to 6.4 switch in the Bentley. 
That reading is in BAR, in which 1 BAR = 14psi. So, 2.1 BAR = 29.4 psi. Now, 
anytime the oil pressure is too low, the buzzer should come on with the 
light. However, I believe there is some sort of delay built into the system 
that will keep it from buzzing during the first few seconds after startup.

On the subject of the bypass valve, there isn's such a thing that I'm aware 
of in the actual oiling system. Your opperating pressures will be quite a 
bit higher than that, especially when cold. From my experience an engine 
wouldn't run very long at high RPM's on 22 psi oil pressure.

As for the actual oil pressure, there really is no "ideal" oil pressure. It 
varies from engine to engine. There are guidelines, however, which is why VW 
put a range into the warning system. However, your oil pressure should be 
higher when cold, due to thicker oil. It also should not drop below about 
15-20 psi at idle when warm. If it does, no matter what engine we are 
discussing, your tolerance for the engine bearings is too high.

I'm guessing that you aren't having any problems, as you didn't give any 
specific troubles with your car?

Tony Hoffman
----- Original Message ----- 
From: "Bryan K Walton" <bryankwalton at machlink.com>
To: <vwdiesel at vwfans.com>
Sent: Friday, September 01, 2006 6:24 AM
Subject: [Vwdiesel] Oil Pressure Warning System on '84 Rabbit


> I'm trying to understand the oil pressure warning system on my '84
> (non-turbo) Rabbit.

>
> What I'm SURE I don't understand is the following:
>
> 1. If the first switch only operates between 2.1 and 6.4psi, and the
> second one only operates between 23-29psi, what happens if the
> engine is over 2000rpms BUT the pressure is somewhere between 6.4 and
> 23psi?
>
> 2. Bentley seems to say that there is a oil pressure bypass valve that
> sends oil back to the crankcase IF the pressure gets over 22psi.  That
> would seem to tell me that the pressure should NEVER be more than
> 22psi.  But Bentley also says that the minimally acceptable oil
> pressure at 2000rpms is 29psi.  So, what am I misunderstanding here?
>
> 3. Final question, if the ideal oil pressure at 2000 rpms is 29psi,
> can I extrapolate that ideal pressure at the following rpms is:
> 1000 rpms: 15psi
> 3000 rpms: 44psi
> 4000 rpms: 59psi
> etc...
>
> Can somebody please shine some light on my mental shortcomings here?
> Thanks!
> Bryan Walton
>