Ooops. last service was on 3/25/2022 when the mileage was 39,920. Service included new Amsoil synthetic 0-16, new OF, new plugs, etc. Today the mileage is 42,600. Do I need to get the car serviced. now again?
Your oil is fine as far as mileage, but in my car I like to change it out every 5 to 6 months if I have not hit the mileage where I change it out. You got almost a year on that oil and filter. Should not need service on anything else. Hopefully, you can change your own oil so you are saving money. It would not have anything to do with your mpg issue.
But as others have stated, The first thing I would do would be to hook up my OBDII reader and look at my live data. Buying one is cheaper than what it would cost you to go to any local shop and have them hook theirs up and look at the numbers for you.
This is the one I use, it is pretty basic, not super fancy but it does have live data and can read your fuel trims. The OBDII can get kind of complicated, they can do a lot of things, but you do not need to know how to do all those things, you can learn them one at a time. For your fuel trims, it is pretty easy. Hook up the reader to the port, allow it to connect to your system, start your car up and let it idle, on the obd, go to live data and just scroll down to your fuel trims. There will be long-term LTFT which is your average fuel trim over time and there will be STFT which is your current fuel trim numbers. Just look at the STFT and observe the number next to it. A negative number indicates the computer is holding back fuel from the injectors and a positive number is a computer adding fuel to the injectors. What you really want is a STFT of 0.0, that would be perfect, but you rarely see that. In my Lexus, I believe the normal acceptable range is +10 to -10. If you see a STFT number over 10, lets say +26 or something like that, This could indicate something like a leaky or loose vacuum hose. If the number looks good then you can at least rule this out as a cause of the MPG issue. If it is an issue as some have stated that it is normal for your car to get those numbers.
As for someone mentioning, asking if your trans is going into overdrive, it is just the high gear. So lets say you are cruising down the hwy at 60mph, what is your RPM gauge reading? If your trans is not going into the high gear and staying a gear lower, it is going to be running at a higher RMP and eating up more fuel. I do not know what the normal RMP at highway speed is for your car but others here have the same vehicle and can tell you if it is normal, for instance, my lexus at highway speed is right at 2,000RPM, If I was not in OD and accidently left the gear shift in 4 rather than D I would be at like 3000RPM or there about. And that would be eating up my fuel. Some vehicles you could be out of OD and not even notice if you are not paying attention and you would not get any kind of engine light for that.
