Hi newagetomboy. That's a lot of questions.
There's a couple of ways to do this. One is to use your Mirage display to do it for you. It has two MPG displays - we can help you understand how they both work.
The other method is to do the math yourself.
1. Fill up your tank and note the mileage on your odometer.
2. Drive.
3. Fill up again and note both the mileage on your odometer and the amount of gas you filled up with.
4. Divide the total number of miles you drove by the amount of gas you purchased to figure your Miles Per Gallon.
5. Do this over several tanks to get an average figure, rather than just one or two tanks.
This must be the maintenance reminder. We can help you understand how this works too.
87 gas if fine. There should be no need to use any fuel treatment if you use good gas.
No, I don't think this is necessary either.
It sounds expensive. It's not available in my market so I have no experience with it.
Well, you shouldn't have to buy high-priced gas, but you could avoid purchasing additives if you stick to Top Tier gas. Read all about it here:
TopTierGas.com
Like inuvik said, get that alignment checked. Having your wheels pointed in different directions will cause fast & uneven tire wear.
One way to see how much gas your little car can hold is to run it out. One problem with that (besides being stranded...
) is the fuel pump, located in the fuel tank, is both cooled and lubricated by the gasoline. By running out it *may* cause damage to the pump. Now, I would hope the fuel pump would survive one or two incidents of being run dry, but I would advise against making a habit of it.
Regarding your owner's manual: You really ought to read it. Your Mirage has some pretty cool features that you might not know about, and learning more about your car will help you enjoy & appreciate it even more. You could download a copy through Mitsubishi and read some while waiting for your next fare. Aside from that, we will do our best here on the forum to help you out.
Glad to know you are getting great use out of your Mirage! I remember when you first joined - I was curious to know how your repairs turned out. It sounds like everything is going your way.
Tell us more about how your Mirage is working for you doing ride share and with regular use, and also what your riders think about it.