sure, I can explain that system.

there really isn't enough information yet to really 'know' what is really going on though. 

replacing the oil pressure switches is a common, semi-easy and logical thing to do.
I seldom ever, ever find a bad oil pressure switch.
like maybe 1 in 400.
but those are inexpensive parts.....could fit the symptom , so logical to try new ones.

be SURE to get the right one for each location.
obvisously they have different bar ratings ( or psi ratings ) 
and ...the one by the crankshaft pulley uses reverse logic compared to all 'normal' oil pressure switches.

it is 'open' where there is no oil pressure ( or below it's trigger threashold ) 
and supplies ground when there is enough oil pressure to keep it happy.
for example..
if it was faulty and not supplying ground when there is good OP ...you could just ground the wire going to it, to keep the DOPS from firing off the buzzer or warning light.
that's what we do on subaru conversions in an 86 or later van ...
since there is only the one normal OP sw on a soobie engine.

the way the DOPS works...
it's 'smart' in that it distinquishes between high and low rpm oil pressure.
it takes an input from the tach so it knows where engine rpm is.

this is because ..supposing you only had 10 psi at 2,500 rpm ..
on a 'normal' single OP swtich cirucit..
where the treashold to trigger the light is about 7 psi ..
from the driver's seat, things would seem fine, ..
but really ...10 psi at 2,500 rpm is very low.

that's why the DOPS has high and low rpm oil pressure sensing functions.
the circuit itself is hidden inside the speedometer.

the only 'real' way to know  is checking the actual oil pressure with an oil pressure guage. 

only then do you really know if it's a sensor/indicator problem, or actual low oil pressure .

or you 'try things' ... thcker oil , new OP switches ec. 

scott
turbovans
  ----- Original Message ----- 
  From: Jim Arnott 
  To: Vanagon List ; vw-wet Wet 
  Cc: Eric Johnson ; Clif 
  Sent: Saturday, August 14, 2010 5:18 PM
  Subject: [WetWesties] 2.1 dynamic oil pressure system

    
  So today I had the opportunity to deal with the oil pressure warning 
  system on a 2.1. Unsuccessfully I'm afraid. Here are the details:

  Email from a WetWesties member dead at the side of the road in my part 
  of the world. Blinking oil light and buzzer. '89 Syncro. Initial 
  indications while climbing a long grade. They noted that the oil level 
  was a bit high so they had the oil drained and correctly filled here 
  in La Grande, OR before continuing on their way. 20 miles out of town 
  at the top of a long grade, the oil pressure light starts blinking and 
  the buzzer goes off. They shut it down and call a tow back to La 
  Grande. Holler for help on the WetWesties list. I gotta go, ya know?

  Fast forward three hours. Both oil pressure switches replaced. 5W30 
  oil drained and replaced with 3.5 quarts of 15W40 Delo. No lights, no 
  buzzer, no leaks. Off these nice folks go on their trip to 
  Yellowstone. Thirty minutes later, the cell goes off. Clif & Amy. 
  Same place, same symptoms. Want advise. I dunno. Chat further and find 
  out that there is no lifter clatter at any engine speed. Above 3k rpm 
  the light and buzzer go off. 300 miles home, 100 miles to Boise and 
  Wagonworks. Tough call. So.... Since I really don't understand how 
  the later model oil pressure warning system works, I'm not sure 
  whether they have a real engine problem or an indicator problem.

  Can the wisdom of the lists bring me up to speed on how the 2.1 OP 
  warning system works. Oil pressure problem or sensor problem?

  Thanks in advance.

  Jim

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