The image may be grainy and out of focus because the projector may not be at the recommended viewing distance which is 5.2 - 32.7 ft. Adjusting the zoom lens may also help remedy the problem. If this still isn't fixing the problem you may need to take apart the device and clean the bulb/lens.
Your device may be overheating because the fan is dirty or the fan is broken. You filter may also be clogged and dirty which is preventing the fan from running correctly which results in overheating.