My fathers 1999 F-250 super duty has been sitting for probably 6 years now. It was running when parked but he became ill and could not drive anymore. It has been sitting outside uncovered under trees the inside shows signs of mice. I threw a new battery in her and was able to get her going but i dont wanna just start driving it without making sure everything is good. What would you do? Change all the fluids? Air filter for rats nest? Do the injectors need to be cleaned or anything?

 

Get some fresh gas in there or drain tank...change fuel filter after running for a while.... Check for rust/lines etc
Basically get her safe first then you can change all the fluids...Smell the gas ! Has it turned?
Rust might be an issue being from Me.

 

you did not mention if this is a gas or diesel engine .

 

gasoline v10

 

I believe the wiring on your truck had a soy based insulation on the wires. My 2000 did. Mice liked to chew on the wiring. You may have some wiring to repair. The local Ford dealer was good at finding and fixing this the 3 times it happened to me.

 

Get some inexpensive oil, an oil filter and an air filter. Check the fuel and transmission lines for rot, repair as needed. If there's more than 1/4 tank of fuel, I'd drain it. If there's 1/4 tank or less, I'd top the tank off with fresh fuel with a fuel stabilizer and a fuel system cleaner. Check for transmission fluid on the dipstick, oil and coolant level. Change the air filter. After that, with the old oil still in it, I'd run it at idle till it gets up to temp and the thermostat opens. I'd be keeping an eye out for any leaks/smoke/unusual noises while it's running. Get in the truck and move the shifter through all the gears make sure you can feel drive and reverse engage, maybe let it roll, at idle, a few feet each way if it will. Then check the transmission fluid while it's running. Shut it down and change the oil and oil filter. Once it's cool, check the coolant. Next step would be to check the brakes lines for rot and pull the brakes for an inspection/cleaning. If you get into replacing lines it'd be a good point to flush the brake system. Do a quick check of the suspension and grease up what you can, nothing should go bad from sitting so it's probably fine. At that point it should be safe to drive around, gently, to get everything lubed and moving again. After about 500 miles or so I'd change the oil again, along with the transmission fluid and filter and I'd probably throw a new fuel filter in it.

The engine will probably be fine, but my main concern would be the transmission. I've seen where a transmission sits for long periods and will get some rust on the steel plates just from moisture in the air and the clutch plates dry up. Then you go to drive it, glaze the clutch packs and it starts slipping. Once you get it running, every day for 2 or 3 days, run it up to temp and move the shifter through the gears so it's circulating transmission fluid. Then let it sit overnight. Transmission fluid has rust inhibitors in it. If you get the fluid circulating a few days before you actually drive it it'll break down some of the rust and it'll soak the clutches in fluid so they aren't dry. Then just drive it easy. Like 90 year old grandma easy until you've put at least a couple hundred miles on it.