Most modern buses have a service coolant valve. Start engine, at hi idle if possible, check all coolant hoses and follow heat path. Easy fix.
Finding any battery load or loss is also easy to fix and find. Disconnect the negative battery cable. Connect any lite between cable and ground bolt or stud. If lite is on, there is a battery voltage leak. Slowly remove all the fuses. When load loss is discovered, lite will be out. Frank in Idaho..