2008 Nissan Altima 2.5s is burning through gas like crazy! Motor has 164k on it. I put in a half tank yesterday and I've only gone about 50 miles, 80% Highway and I currently have 36 miles remaining. The tires are all inflated and air filter is clean. There's no noticeable gas leaks. What can I do?? This has been an issue for about a month
First, make sure you do not loose fuel anywhere. May sound stupid, but a leakage in the fuel system can be kind of hard to detect, since gasoline quickly evaporates. Look under the car while it is running and also look closely at the fuel-rails.
If you can, see if the engine reports any errors via OBDII-Port. Cheap readers for your smartphone are available and also a local should should be able to do this for a small fee.
Then check the usual components and when they where last serviced. Fuel filter, air filter, spark plugs. Replace where necessary. Take a look at your spark plugs - do they look healthy?
If the car injects to much fuel (generally runs rich), you should check your airflow-meter and O2 sensors. Also inspect the vacuum system for leakage.
If you see signs of misfire, inspect/replace your ignition coils.