Thanks Chris, the stern drive is new, SEI Alpha, I removed the starboard side exhaust at the rubber fittings and the water is flowing well' It comes out the top section of the riser and then joins the exhaust gas. There is a lot of corrosion and some small pieces were removed with a magnetic flexi stick. I take it that the block is therefore being cooled correctly, just a restriction at the water exit point in the gimbal exit. as there is some flow. Once the engine is warm, I can still put my hand in the hot water. I assume the exhaust gas and water meet down the bottom and the water is being 'forced' out the prop due to the restriction. I take its OK to run the motor like this as its still being fully cooled? And then do a rebuild in the winter, I'm in Sydney.