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Oil Pressure Switches
04-17-2019, 07:10 PM (This post was last modified: 04-17-2019 09:24 PM by Adrian.)
Post: #1
Oil Pressure Switches
Hi All,

My 2.6 I5 has the two oil pressure switches on the right hand side below each other. Does it matter whether the oil pressure switches are swapped i.e. are they connected to the same or different oil passages?

The oil buzzer keeps coming on below 2k rpm when at operating temperature.
* Blue/black wire connected to low pressure switch (wires swapped in picture).
* Pressure switches are brand new.
* Low pressure switch in the bottom location
* Image view is from the top looking down.

Thanks for any feedback
Adrian


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'89 Syncro 2.6i "ZIP"
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05-11-2019, 06:55 PM
Post: #2
RE: Oil Pressure Switches
(04-17-2019 07:10 PM)Adrian Wrote:  Hi All,

My 2.6 I5 has the two oil pressure switches on the right hand side below each other. Does it matter whether the oil pressure switches are swapped i.e. are they connected to the same or different oil passages?

The oil buzzer keeps coming on below 2k rpm when at operating temperature.
* Blue/black wire connected to low pressure switch (wires swapped in picture).
* Pressure switches are brand new.
* Low pressure switch in the bottom location
* Image view is from the top looking down.

Thanks for any feedback
Adrian

Hi Adrian,

The switches are on the same oil gallery. What is important for the logic of the buzzer circuit is that the yellow wire needs to go to the switch that is "normally open" (NO) and this is indicated by the colour of the switch. The NO switch has the higher pressure rating of 1.5 to 2.0 Bar and VW usually colour this switch white or plastic of opaque look. (after-market switches do not necessarily follow this rule) The second switch that must be connected to the blue/black wire is the "normally closed" (NC) type and VW colour is usually blue. One can test the static NO and NC condition with an ohmmeter, with the NC switch indicating short circuit (0 Ohms) with no pressure on it and the NO switch giving no reading when NOT under pressure. The NO switch will close at the rated pressure and then also give a short circuit or 0 Ohms reading. Obviously the NO switch can be tested while the engine is running... it should always remain closed during engine running condition. The third condition that the buzzer circuit monitors is the RPM value that originates from the ignition circuit and feeds both the rev counter and the buzzer circuit in the instrument cluster. At a value above 1500 RPM the buzzer circuit checks for the presence of the two inputs coming from the oil pressure senders and these inputs switch sequentially to OFF condition from the low pressure sender (blue/black wire) and ON condition from the high pressure sender in that order. In this state, the buzzer initializes and should remain off. The logic circuit is sensitive to the sequence of switching and obviously the low pressure sender operates FIRST followed by the high pressure sender. A change in the state of the pressure switches after initialization will set off the buzzer. Check your switches to be NO and NC and connect wires accordingly. Low oil pressure is not uncommon in the 5 cylinder engine at idle with hot oil and the reason is often attributable to the oil sprayers in the engine block that allow quite a large amount of oil to escape from the pump supply. Other than the irritation of the buzzer, I wouldn't worry too much about low pressure at idling... just ensure good pressure at running condition... get an oil pressure gauge to check this. You can select a lower rating for the high pressure sender to silence the buzzer but don't go lower than 0.75 Bar.
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