Club 80-90 Forums

1.9DG in a 1990 model - although VW recond unit installed last year (taken from scrapper).

I have blinking Low Oil Pressure light - comes on at about 10 mins driving - usually at higher revs. Then continues to blink at me - with no sign of the buzzer.....
First time I stopped - turned off - checked oil - waited - turned back on - then fine for next half hour (end of journey) - then on return trip same - blinking after 10 mins. Turn off - turn back on - no blinking etc. Has done this on a couple of trips - no other indication of owt amiss - mpg OK - running on gas and petrol OK - I did change from VW Quantum 10-40 to a 10-30 as the temp up here has been down to -10 to -6 every night for 2 weeks and not above freezing in the day (straws being grasped there I know).

In hope (obviously) I am going down the faulty switch route and have van booked in Thursday for oil pressure test and switches replaced. I know I should be looking at the PCB end too - but there is nearly two foot of snow out there !!

Now which switches to order from VW....??

From WIKI -
Low rpm/low pressure sensor - 028 919 081 D (0.25 bar BLUE) - Later replacememt for all .3bar switches (OK - I am good on that one)

But which of the following please ??
High rpm/low pressure sensor (Petrols) - 068 919 081 A (0.9 bar GREY) - Std. 2.1
High rpm/low pressure sensor (Petrols) - 068 919 081 E (1.8 bar WHITE)

ANy help appreciated.

In very cold weather usng a 5w40 might be ok.. but 10w40 would be ok in anycase, but a 15w40 is the std "all weather oil.. and a normal mineral oil is best.. the lower second number (30) means its thinner when hot... not what you want really..
I'd be at least filling with 10w40 ASAP...
No buzzer??? late models have a second oil pressure switch.. this activates a buzzer and light when decelerating from above 2000rpm..

Light seems to come on for first time when accelerating (above 2000 revs)?

I would be putting some thicker oil in to start as if it really is low oil pressure, then it WILL damage the bearings... then change the pressure switch as its not uncommon for them to fail.. Brickwerks has them too..

Anyone know If I need a Blue (low revs) and Grey (0.9) or Blue and White (1.??

I'd be checking that someone hasn't earthed out 'The Buzzer Of Doom' (BOD) this is the switch which is next to the oil pump.

Ian.

You want the brown (081C) or the blue (as you cited, 081D) switch for the low-OP circuit. That switch is situated between the pushrod tubes lower left side of engine.

You definitely want the grey (081A, 0.9bar NO) for the hi-OP switch, below and to the right of the water pump pulley. Using the white 1.8 bar switch there would give you nuisance warnings even with pretty healthy OP. This switch also has to be a normally-open (NO) type, whereas the low-OP switch is normally-closed (NC).

The 1.8 bar switch was never used on the wbx but it is shown erroneously on some of the Bentley wiring schematic pages.

Remove the belts and water pump pulley wheel to gain better access to the hi-OP switch.

The low-OP switch is NC and grounds the idiot light circuit. It opens at 0.25 or 0.3 bar OP which opens the circuit so the idiot light goes out. This is exactly the same as has been done in just about every car, certainly every VW, since such things existed.

But, the hi-OP switch is NO. It closes to ground the sensing wire from the Dynamic OP Warning System controller when OP is over 0.9bar. So if OP falls below 0.9bar AND rpms are over 2k, the controller sounds the buzzer and makes the idiot light blink. People usually get this warning when decelerating from higher rpms, like Si said, because it is high rpm cruising that heats the oil the most, so as rpms are falling after a good cruise, the OP drops into the switching range and the warning is triggered, but you can get the warning at any time those two conditions are met. You sometimes have to switch the ignition off and back on to reset the warning, although there seems to be some variation of this requirement from car to car.

So if you want to test the hi-OP part of the warning system, just disconnect the hi-OP switch's wire (you can intercept it at the two-pin connector in the left-front corner of the engine bay, near the t-stat housing) and rev the engine over 2k. You should get the buzzer and blinking light every time you open the circuit and rev past 2k (or so).

You can see by this logic that the system is dependent on continuity to ground of the hi-OP switch's wire, so:

a.) the dynamic system can be defeated by grounding the hi-OP wire permanently; this is often done when people install a late instrument cluster in an earlier van whose wbx does not have the hi-OP switch fitted.

b.) if there is a break in the hi-OP switch wire, or loose connections, the dynamic warning will go off intermittently. So not only does the hi-OP switch itself need to be dependable, but the circuit also has to be solid.

If you deliberately ground the hi-OP switch wire, and still get the buzzer when revs go over 2k, then you may need to get at the back of the instrument cluster to be sure the connections and the circuit foil are OK such that the rpm signal is reaching the warning controller (housed in the speedo head).

The OP switches, whatever color, are like any switch or sensor, prone to failure after some years in service. They can get dirty and sticky internally so that they don't trigger when they should (clean oil helps here since that's where the gunk comes from), but most often they begin to seep oil externally around the plastic insert part of the switch. The seepage can progress to spewing oil, which can dump a lot of oil while pretty much assuring you get no warning because the switch is usually inop when that happens, so if any of your OP switches are seeping, that is all the early warning you'll likely receive. Replace them! They're very cheap.

Ride on my English brothers!

I am privileged to receive a reply from the esteemed poster above (known to those Brits who lurk on the Samba/Vanagon site) for his knowledge and being so prepared to share it readily. Many thanks for the comprehensive reply (and to the others above too )

Now can anyone fix my other car - a Skoda which unlocked itself and whose windows all wound down by themselves during a snow shower this afternoon........ Am off to clear the garage to get it undercover as we have 6 inches due tonight....

Thanks Tencentlife for the above response to mikey9's query.

I have been looking around for details of the BOD ('buzzer of doom') and the DOPWS as I too have been having 'issues' with the buzzer and/or low oil pressure! The above answer is the best response I've seen.

Having looked to change the switches I note my high rpm /low pressure switch (the one mounted near the water pump) is a white one, so perhaps that alone has been causing my problems. I believe from the above that I should fit the grey one so I will do that. However, I have one question, and one observation.

Question: What SHOULD the oil pressure be for a 1.9DG engine (1986)? Both at idle and above about 2000 rpm? I've searched around but can't see any confirmed numbers. I'd like to fit a pressure guage at some point, but unless I know what the pressure should be I'd still be worrying!! I'm also surprised that the white switch causes the buzzer to go off if there is good oil pressure as 1.8 bar still seems quite low to me? Comments?

Observation: Having read all the threads / wiki entries on the BOD and the DOPWS it appears that Tentcentlife's explanation of which pressure switch does what is the most common - i.e. that the blue low/low switch just controls the warning light when low RPM and the high/low switch is the one that triggers the buzzer. However, the Wiki entry (https://club8090.co.uk/wiki/Al ... and_causes" onclick="window.open(this.href);return false;) states the opposite - 'The flashing oil pressure light and 'buzzer of doom' are operated by the low-low pressure switch, hence at lower engine speeds'. i.e. that the low rpm / low pressure switch triggers the buzzer of doom. I assume this is incorrect? Can someone please confirm - and how do we go about getting it corrected? No doubt it will confuse others as well as me so it would be good to get it changed if it's wrong.

I'm afraid that wiki is incorrect, at least as you've cited it. The low-OP switch isn't really involved in the DOPWS; the low-OP switch lead is actually tied into the controller but as far as I can tell the controller doesn't care what it sees on the wire to the low-OP switch, grounded or not. It wouldn't make sense for it to care, actually, if OP fell below 0.9bar at 2krpm, the low-OP switch could be in either state, either above 0.3 bar, or below it in the case of total loss of OP, and in either case you would want the warning to sound. So logically the state of the low-OP switch shouldn't matter and as far as I can tell in practice, it doesn't.

But there is no doubt at all that it's the hi-OP switch circuit that triggers the BOD, the repair manual even explains how to test the system using that lead to trigger it.

VW does issue one single spec for OP, which is that at 80C oil temp the OP should be 2bar at 2krpm. You'll see that on a nice tight wbx but I would say most run below that level, and they're still OK. As a general rule, with most pressure-lubed engines, you'd like to see about 10psi (0.7bar) per 1000rpm. I think that rule holds to about 4krpm whereabouts OP will often peak and that's fine, you'd never need more than 3bar of OP at normal operating temp.

You can see by the rule of thumb that at 2krpm you'd only have about 1.4bar, which is still a quite healthy engine OP-wise. But if you had the white 1.8bar switch you'd get nuisance warnings every time the rpms transited thru this range of rpm/OP, until either rpms climb and OP rises above 1.8bar, or rpm falls below the 2krpm threshhold. These figures of rpm and OP are not precise, either, the OP-switches have a fairly wide tolerance around their switching points and the rpm at which the BOD gets triggered seems not to always be precisely 2k.

Hope that helps.

Thanks, that's a really complete and useful answer that helps a lot!

I'll head home now to fit the grey 0.9 bar switch with more confidence that assuming it doesn't set off the buzzer with that one in there all is fine!

Thanks again.