Abstract: An oil pan is provided with a partition member so as to be divided into a main chamber and an antechamber. A vertical wall of the partition member is provided at a lower region thereof with first holes adjacent to an opening of a draft tube of an oil pump and at an upper region thereof with second holes in the vicinity of an oil level. In a state of warming up following the starting, since the oil temperature is low and the viscosity of the oil is large, the oil in the antechamber cannot pass through the first holes. Accordingly, only the oil in the main chamber a quantity of which is small is circulated through the engine by the oil pump, thereby warming up the engine quickly. Low temperature oil in the antechamber is interchanged with the oil in the main chamber little by little through the second holes, so that the temperature thereof is raised gradually.

Abstract: A reference electrode is formed of lead, zinc, tin, indium, cadmium, magnesium, or any alloy thereof. A pair of electrodes comprising the reference electrode and a responding electrode made of a conductive solid, when placed in oil, develop a potential difference varying with the acidity or basicity of the oil and thus enable the efficient determination of the acidity or basicity.