Abstract: A shock absorber system where an outer cylinder having a top closure is connected to a vehicle frame and having a ported bottom closure. An inner cylinder is mounted coaxially in the outer cylinder and has a main piston including a piston rod extending down through the ported bottom closure. The piston is in slidable fluid tight relation to be connected to an axle of the vehicle. The system further includes a cooling cylinder and structure forming a flow channel leading into the cooling cylinder from beneath the main piston. Structure forms a return flow channel from the cooling cylinder into the top of the inner cylinder and includes a check valve. The cooling cylinder includes a gas pressure positioned free piston. Structure further includes a check valve in the main piston for passing liquid from above the main piston to below the main piston upon compression of the main piston and for circulating fluid through the cooling cylinder upon expansion.