RangeR BoB's Audi A4 oil pressure sender installation page

The problem was, that to install the oil pressure sender for the gauge, I had to remove one of the two oil pressure switches used by my engine's computer to keep tabs on oil pressure. The switch I removed is located on the back of the oil filter adapter on the Driver's side of the engine. It has a single wire connected with a spade lug and covered with a white rubber boot:

You can best see it by moving the coolant reservoir tank out of the way.

This switch is used by the computer to be sure that oil pressure is above 1.2 bar by the time engine revs get above 2000 rpm. When I removed this switch and replaced it with the pressure sender, I got a persistent beeping warning and flashing red light on the dash when the engine revved above 2000 rpm because the switch was not triggered. The computer was just trying to help, but I needed to solve the problem.

To cure this problem, I removed the oil pressure sender and replaced it with a T-fitting from VDO. Into this fitting I can screw both the Audi factory Pressure Switch and the Autometer oil Pressure Gauge Pressure Sender. I used VDO part number 240 850, which I ordered from Summit Racing.

These installation instructions will also work for those of you who want to install an oil pressure gauge from scratch.

First we have to remove the coolant tank. We don't want to drain the tank, but luckily there is enough hose so you can move it aside w/o disconnecting anything.

First you have to remove the 3 screws that hold the tank to the car:

Flip the tank up towards the front of the car, and unhook the wire connector for the coolant level sensor from the bottom of the tank.

That done, we expose the sensor location. Slide back the white rubber boot, and disconnect the spade connector from the switch.

Remove the switch with a 24mm wrench.

To install an Autometer gauge, you need to know about threads. The sensors on Audis are straight (no taper) metric 10mmx1 thread (10mm diameter, 1mm per turn threads). The seal is achieved by flat machined surfaces on the switch and the oil filter adapter body. No gasket is used. I believe VDO senders are also 10mmx1 thread. I used an Autometer gauge kit, and the Autometer sensor is US 1/8" NPT (National pipe thread, a tapered thread system based on the ID of the pipe, not the diameter of the threads themselves). The seal with NPT is achieved by the crush fit between the tapered threads. 1/8" NPT will start to thread into the 10mmx1 Audi threads, but Don't Do It! It will leak! So you need to get an 1/8" NPT to 10mmx1 adapter, like shown here:

You need to seal the threads with thread sealant like this:

Put a nice even layer of goop like this on it (note this photo was taken after the sender and adapter were married up, but you get the idea):

Thread the sender into the adapter. Use a 14mm wrench on the adapter and a 9/16" on the sender. (note the 100 psi rating on the sender)

Next goop up the adapter threads and thread the combined sender/adapter into the T-fitting, using the 9/16" on the T-fitting, and the 14mm on the adapter:

You can't install the pressure switch into the side port of the T-fitting until after it is properly seated in the oil filter adapter, because it will interfere with various things while you try to screw it in. So we will install the T-fitting and Oil Pressure Sender first, then add the pressure switch later.

Goop up the threads of the T-fitting and begin to install the T-fitting into the oil filter adapter on the motor. Use the 9/16" wrench on the flats of the T-fitting for leverage.

You are going to have to "clock" the T fitting in the oil filter adapter housing so that the side port is arranged in a location that will allow you to insert the switch. If you just tighten the T-fitting until it is tight, chances are that you won't be able to install the switch. "Clocking" involves rotating the T-fitting slowly until it bottoms out in the oil filter adapter housing. If you are lucky, at the point where it bottoms out you will be able to insert the switch. There is a certain orientation where the switch will thread in as shown:

If you are unlucky, you will have to slowly turn the brass T-fitting into the oil filter housing. The housing is zinc diecast metal, so it is softer than the brass. The sharp corners of the brass T-Fitting will remove a bit of the softer zinc casting, in effect "spot facing" the casting so that the T-fitting can be rotated to the correct orientation. Slow steady pressure on the wrench will make this happen. No sudden movements, and if you feel the tension level suddenly spike, Stop! If you break off the T-fitting, you will have hell getting the threaded spud that will remain in the casting out.

Once you have it clocked to the right orientation, we are going to try a dry-run with the switch. First, please clean the threads of the switch to remove any residual oil. Now try screwing it in. There are various protrusions and such that will play havoc with your installation. If the switch interferes with anything, try "clocking" the adapter a bit more until nothing is in the way. That checked, remove the switch. Again goop up your threads on the switch with teflon sealant, and screw in the switch by hand. I was not able to get a socket in there to tighten it, so I ended up using the 24 mm open end wrench like a fork, perpendicular to the flats of the switch rather than parallel to the flats, and I turned the 24 mm wrench with an adjustable Crescent wrench to tighten up the sensor.
Once the pressure switch is screwed in, reconnect the wire and the white rubber boot.

Now clean up the area with a rag to remove any squeezed out sealant or metal shavings from the spot facing of the oil filter adapter housing. Watch out for the metal shavings! They'll poke you!

Now you are ready to fire up the motor and check for leaks. You can run it for a few minutes with the coolant reservoir out of position and it won't hurt anything. Just make sure no hoses are pinched

If there are no leaks, all is well. Now you need to reinstall the coolant level sensor plug to the bottom of the coolant reservoir and replace the reservoir in its mounts and screw down the 3 mounting screws.

Have a beer!