Date:         Thu, 16 Aug 2012 16:56:51 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Oil preasure light
Comments: To: C Snyder <titantic01@AOL.COM>
In-Reply-To:  <643E630D-DE89-429D-89BA-E62E981E92DD@phoenix.aol.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 01:49 PM 8/16/2012, C Snyder wrote:
>I just had a new oil preasure sending unit (the one that goes on the
>drivers side between the push rod tubs) on my 2wd 1987 Vanagon. When
>the key is turned to on the oil light blinks to chk the bulb then
>goes out. Is this normal? Any other car the light stays on until
>after the engine is started. Is this a design thing on Volkswagon vans?

Since by definition there is no oil pressure and 0 rpm when the
engine has not yet been started, the 0.3 bar sender switch is closed,
the 0.9 bar sender switch is open, and the two-level (DOPS - Dynamic
Oil Pressure Sensing) system used on the 2.1l engines will show the
standard indication for low-rpm insufficient pressure, a constant
blinking LED.  Having the LED stop flashing at this point is NOT
normal (and Ken knows this, he just had a brain fart).

Once the engine is turning and oil pressure rises above ~4.5 psig
(0.3 bar) the 0.3 bar sender switch opens.  The DOPS circuit checks
engine rpm and finding it below 2,000 rpm, shuts off the blinking LED.

As pressure continues to rise past ~13.5 psig (0.9 bar) the 0.9 bar
switch closes.  This is ignored while rpm stays below 2,000 rpm.

While engine rpm is above 2,000 rpm, should the 0.9 bar switch open
the LED will flash and a buzzer will sound.  Once rpm falls below
2,000 the 0.9 bar switch is again ignored.

If the cold engine is stopped immediately on starting (in cold
weather) and the ignition turned bad on you'll be able to see a delay
of several seconds before pressure drops enough to close the 0.3 bar
switch and trigger the blinking LED again.

This leaves undefined (by me) a number of conditions; for example,
what happens over 2,000 rpm should the 0.3 bar switch close but the
0.9 bar switch fail to open?  I could argue for my version of how it
ought to behave, but as I've not yet tested it I can't promise that
it was built the way I would have done.

Yours,
David