Bryan,

You can also use an airspeed indicator, if you have one handy.

The key is that both "tubes" that pick up the pressure have to be configured as if they are static pressure ports.  This means that the air has to flow over the opening(s) in the tube at 90 degrees, like the static port on the fuselage.

An easy way to do this is to use a short piece of tubing with holes drilled in the sides, like a soaker hose for the lawn.  Smash one end of this tube completely and connect the line back to the sensor to the other end of the tube.  Point the closed end of the tube directly into the airflow.  Do this to both of the tubes.  One would be at the oil cooler inlet, the other at the outlet.  You will now sense the difference in the local static pressure at these two points.  You can do the same thing anywhere else in the engine compartment that you like.  For example, you can measure the differential pressure above and below cylinders to ensure you have adequate cooling flow.  Chris Z., is about 5" of water pressure the figure Bryan will want for cylinder cooling?

If you are using an airspeed indicator, you will have to google for the conversion of speed sensed to pressure in whatever units you like.  Same for some other pressure measuring device.

For my purposes, I designed, and 3 of us built, an electronic 4-channel sensor that can display data from one channel at a time in the cockpit during flight.  I do need to have a secretary on board to take data readings and flip the switch between channels.

Goog luck,

Tom Thibault