I have a 1994 150 HP Johnson and the warning horn is sounding about every 30 seconds. Even when the engine is not running. The oil tank is completely full of new oil.
You can check the filter/screen at the pickup at the bottom of the tank and make sure that it is clean. (yes it is a messy job). Also the sensor can go bad.
Yes, drain and clean thoroughly and fill with new oil. It's not a good idea to mix brands as some will congeal over time. If this dosn't clear it, check your sensor.
lund,<br /><br />Drain and clean it. Replace the filter sock.<br /><br />Don't forget to pre-mix 50:1 until you verify oil useage again from your oil tank.
