Oil-level sensors (an example from Hella is pictured) are used in some modern engines to monitor static and dynamic oil
levels. In combination with an oil-temperature sensor, the data measured can be used as inputs for oil-degradation algorithms in the engine-control unit (ECU) to calculate service intervals. The principle of operation can either be a simple float-bowl mechanism, electrical-resistance (hot-wire) method or even ultrasonic sensors that rely on the sonar principle. It is difficult to calculate the static oil level of a vehicle due to the time taken for the oil to return to the sump and the unknown incline on which the vehicle is parked.
Calibration engineers have come up with an ingenious solution to ensure an accurate oil-level reading when the vehicle is parked on a level surface and the engine is still for long enough. Most filling-station forecourts are level and it takes a set time to fill the tank of a vehicle. After the filling stage, the ECU will trigger the oil-level measurement process when it detects that fuel has been added to the tank. Normally, a couple of readings are taken and then averaged before storing the result in the ECU’s memory. The measurement obviously needs to take place before the engine is started. The dynamic oil level can be monitored while driving but the warning thresholds to the driver will be conservatively calibrated because of all the variables that affect the dynamic oil level while the engine is running.