Abstract: An internal combustion engine for a vehicle includes: an oil tank defining an oil reservoir; a pump to pump oil from the oil reservoir to lubricate parts of the engine; and a cyclonic separator disposed within the oil tank and configured to separate gas from oil received therein, the cyclonic separator defining an internal separator chamber for circulation of oil therein, the cyclonic separator comprising: a vortex forming portion configured to cause oil flowing therethrough within the internal separator chamber to define a spiral path in order to separate at least part of a gas content therefrom; an oil inlet for receiving oil into the internal separator chamber, the oil inlet being fluidly connected to the pump; an oil outlet for discharging oil from the internal separator chamber and into the oil reservoir of the oil tank; and a gas outlet for discharging gas from the internal separator chamber.