Abstract: A flow controlling system having a viscosity sensitive means for producing a simulated fluid pressure which varies in correspondence with a fluid pressure at a predetermined portion of a fluid flow circuit on the basis of the viscosity of the fluid flowing through the circuit, and a pressure regulating means, that is responsive to changes in the simulated pressure, for maintaining a predetermined pressure at that predetermined portion of the fluid flow circuit. In particular, in a preferred embodiment of the invention, the flow controlling system is utilized in an engine timing control tappet system of the type having at least one expansible tappet for controlling timing of a fuel injector using oil that is supplied by a pump to an engine lubrication circuit.