heres what i found , not really sure how true but never hurts to try. its based on V8 but imma give it a shot.

The reason you need an oil temp gauge is because your engine sees the MOST wear when it is cold. Oil temperatures take much longer to get to 'normal operating temp' than your coolant does. This means that just because your engine temperature sensor says that the engine is 'HOT'. it really is NOT and that the oil will not be at operating temp for another 5 miles. This is one reason why bmw M put these oil temp gauges on their M series cars and those little rpm lights to turn back the rev limiter so you cant over rev the engine while cold.

I work for BMW. I have access to all the information I needed to come to the conclusion of how to get the cluster to work properly.

It is all in the coding.

The M5, the 540i, and the v8 x5s all share the same oil level sensor/temperature sensor. All of them are wired up the same.

It is ALL in the coding of the cluster! You have tell the car it is an m5 or a sport package X5 v8 with the fancy gray faced gauges, and an oil temp sensor.

There is no adding sensors or running new wiring. Everything is already there, the 540i just needs to be told that it has an oil temp gauge.

If you go through your OBC tests, you will see one test is for OIL TEMPERATURE which always reads at -40 something degrees just like your ambient temp sensor in the bumper when it isnt connected.

On a side note-

I own a Canadian spec car which reads in metric with no option to turn off the day time running lights which is a law in Canada. I hate DRLS and I had get them off.

I had to go in and tell the car that it was NOT a canadian car and that it was now a USA car. After changed programs, I then had the option to turn off the DRLs along with a few other settings that Canadian cars do not have.