Abstract: An apparatus and method is disclosed for indicating useful life of motor vehicle angine oil during engine operation based on engine oil temperature without direct measurement thereof. Following the initiation of engine operation, engine oil temperature is calculated from a warmup equation until calculated engine oil temperature exceeds a warmup reference, whereupon it is calculated from an equilibrium equation, both of which equations being linear combinations of engine operating parameters other than engine oil temperature itself. The warmup equation includes a constant term, a reference temperature term fixed at the begining of engine operation and a term increasing proportionally with the number of engine cylinder firings. The equilibrium equation includes a constant term, an engine temperature term and a term proportional to engine speed and may also include a term proportional to an engine cooling factor.

Abstract: A motor vehicle engine includes an operator controlled fuel injection enabling switch effective to disconnect electric fuel injection apparatus from an electric power source and thus initiate the cessation of engine operation when deactivated. However, the spark ignition system is still powered through an oil pressure switch so as to continue engine operation for a few extra crankshaft rotations to reduce the unburned fuel in the intake passage as the engine stops and thus reduce throttle bore coking. In a vehicle having a fuel pump relay activated by the fuel injection enabling switch with contacts connected across the oil pressure switch, the invention may be obtained by changing the power connection of the spark ignition system from the fuel injection enabling (ignition) switch to the fuel pump relay.