Testing it in a bag tank or on a lake/pond/river would really be the only practical way to test it for longer periods. You should be fine running for at least 20-30 seconds before shutting it off, especially if it is at low speed and it is cold out. The reason that you cant run motors with rubber impellers long is because the impeller will be damaged due to friction and heat, but with motors such as this that is not so much of a concern as the engine actually overheating. As long as the motor does not get hot enough that the metal of the cylinders/pistons starts to expand with heat, running it for more than 30 seconds but less than a minute at slow-ish speeds should not cause any major issues Otherwise, taking the prop off and trying to spray a hose in the water scoop might work, but it would be easier to test on a lake at that point, even if the weather outside is as frigid as it is in Wisconsin right now.
"Outboards seem to multiply exponentially..........I find that for every finished project, there are two more waiting to be completed."
