First, test the gauge by putting the sender in boiling water. Second, it looks like from your picture that you are hoping that air from the engine compartment will flow through your cooler out behind the car. If I got that right, your cooler is not in a good place as most of the air will go out the vents on the boot cover (I know because I made the same mistake. Your cooler is not completely useless but much less effective than it might be. Is there any reason your oil temps would be too hot? Third, I read many years ago that oil temperature gauges were not normally put in cars because it would scare the driver.