I have to ask what oil change interval is good for a 100,000 mile + ford f150 4.2? Is 1600 miles/3 months good? Or is 3000miles/3months better? I drive 5 miles a day so 20 minimum to 35 miles a week in summer 70 - 90s temperature 10w40 oil castrol; fram regular duty filter.

 

You are driving 1500 miles a year. What has that got to do with 3 months > Most people who drive less than 5000 miles per year will change their oil once per year, no matter what the mileage...... Since you are in florida and it is always warm, that helps with multiple startups/ cold oil..... Most people would have stuck with 10w 30 in the hot weather you have... if you have good luck with 10 w 40, it should not be a big problem.

 

I don't know where you are in florida... there may or may not be excessive humidity........... would be a good idea to look under the fill cap on the valve cover and see if you have any foam or white / oily buildup.......... That can be common for short distance driving, multiple starts, humid weather.... Proper warm up, running 20 miles once a month can help if you have the white foam...Check dipstick to verify that oil is good and OK for a year.

 

you can barely see the oil color, it's so light not new light but very light colored

 

I heard 3 months is a recommend from a mechanic

 

and they say that because they make money doing your oil changes.

As said, an annual oil change is what you need.