What is wrong with my fuel gauge?

I have a 1997 ford explorer v8. The car runs amazing, but i just found out that the fuel gauge doesn't go past half a tank. I put 16 gallons into it and the tank is a 20 gallon tank. What could this be? It took me a week to really notice this. And one more thing, i had my car in the shop to get an oil change, i get it back and the check engin light was on, and i'm pretty sure it wasn't on when i brought it in. Should i bring it back to the shop? The car runs amazing, engin sounds amazing.

I have a 94 ford explorer and the wheel drive won't work?

Both the 4 high and 4 low doesn't work. I checked the hubs and they are fine. I here a click when i press the button and i can hear it click under the truck and the light turns on and everything as if its working but its not engaged. And when i'm driving i can hear it clicking. Any ideas?

How much transmission fluid do I need on a service?

I have a 2003 ford explorer sport trac V6 with automatic transmission. I need to change the fluid but I'm not going to empty the torque converter. If I'm not mistaken it takes 10 quarts to do the whole thing but I just need to know how much just to drop the pan and change the fluid and filter thanks

Who do you contact when a repair shop?

I had a radiator replaced in my 2000 Ford explorer by a certified mechanics shop. They repressurised the cooling system out wherever the coolant flows through the engine. Well when they did that they caused a leak in the middle of the engine. I paid over 600 for the initial job. Now they're saying 1300+! I don't have money like that laying around for a vehicle. They put their hands on it in the first place. Who can I contact to get this matter resolved?
Please and thank you.

Which truck should I buy?

I know they are essentially the same car. I'm a 16 year old guy and I want an SUV for my first car. I'm debating between the 2006 Mercury Mountaineer Premier AWD and the 2006 Ford Explorer Limited 4WD. I have read reviews and didn't find much for bad reviews. They both seemed pretty good mechanically. Which one should I buy?

Added (1). I haven't found any for sale. I just check ebay and autotrader.

Is my alternator broken after mudding?

I went mudding yesterday in my 94 ford explorer XLT during lunch at school, leaving mud on the engine, and when i drove home from school, my battery light was on and my battery was at halfway. It stayed like that my whole trip. I charged my battery last night until it was full and drove to school today. The gauge changed slowly from full to half and then back to full while i was driving. It did this on my way to and from school. When i got home, i washed all of the mud off my engine and let it dry. I turned my car back on and the battery was at halfway still. I just put it on to charge again, and the charger didn't say it was full. Is this my alternator that is shorted out or broken? Or could it just be a problem with the gauge? How much will it cost in Utah to get the alternator fixed?

How often should Coolant be changed?

I have an 01 Explorer sport, 130,000. How often should I change the coolant in my car, and how do I know if its starting to go bad? Gauge says its running at operating temperature(not sure how accurate Ford gauges are though).