Aug 16, 2015 · reason a generac 10 kw standby is blowing oil threw exhaust power went out generator ran for three hours then started to run rough went to see what was going on and there was oil smoke coming out of exhuast what could be the reasons the unit has been working perfect for the past three years till last night Submitted:5 years ago. Feb 27, 2015 · Does your Generac Generator need an oil change? Regular maintenances and oil changes help to keep your generator running properly. It is recommended to change your generator’s oil after the first month or 20 hours of use. After the initial oil change, every 6 months or 100 hours of use is the recommended.