i drive a 1992 nissan sentra. the gas gauge has broken so i use the odometer to know when i need to fill up. i have a ten gallon tank and usually get 300 miles before im bottom empty. but lately i have been getting only 170-180 miles. my oil has been a little low, could this be an oil problem? i checked the odometer and it still works. what could make my gas mileage drop almost fifty percent without any sign? there arent any weird noises or any other type of problem, so....

mrmillion; There are a million things that can cause poor fuel economy. Well, maybe not a million? Tire pressures, air filter, type of driving, ect. Being a Nissan, I'd take a look at the coolant temp sensor. Nissan has a problem with the sensors and connectors. You'll need to have the computer scanned and codes retrieved for us to give you any specific information. With a scanner, you can 'see' what the computer is 'seeing'. Leaking injector(s), any number of sensors, thermostat, primary or secondary ignition faults, ect., ect., ect....
Loren
SW WA

Loren has a lot of great suggestions, as usual. With a 50% loss in fuel economy with no noticeable running problems I would start with the basics, look for a fuel leak and depending on where you live, maybe install a locking gas cap..........