DF9.9 white smoke from exhaust

[Aroamer]

Hi there,

I recently bought a 2008 DF9.9 outboard and have been using it very lightly (15 mins at a time). I have replaced the thermostat, impeller and spark plugs and flushed through with acid solution, but am not sure how well the engine was maintained in the past.

Starts well with one or two coughs, but then settles down to run pretty well. However, I have found the tell to be intermittent (despite changing the impeller) and it sometimes cuts out altogether at idle. It will then also sometimes start to produce white smoke (I assume steam).

I can think of two options - one, there is a cooling issue or two, a head gasket issue. Plugs are not clean though, and given the poor tell I am heading towards a cooling issue. As it is an intermittent issue, I'm thinking it could be a piece of old impeller stuck somewhere in the system.

Any suggestions on where to look first? I've recently had the T-stat and impeller off so I think it's unlikely to be around those places. Any other points in the cooling system that people have found bits to get stuck?

Thanks!

[boats.net]

Was the spark plugs oil fouled or black when you replaced them, is oil thinned out like gas in oil? If they were then need to have a leak down test run to see if rings are sealing. Have you seen any signs of water on spark plugs, usually if have bad head gasket then water gets into cylinder. Some of the small HP motors had water pickup on bottom of ventilation plate of lower unit and if running in neutral sometimes exhaust from prop would interrupt water flow to water pump but as soon as put motor in gear and got under way would have a steady water flow.