I went to the gas station yesterday, I left my truck running while I went inside and came back out my truck had a lot of white smoke coming from under the hood, I shut it off right away because I thought it might be overheating, I couldn’t see any difference in the temperature gage, I turned it on about a minute later And drove home, someone recommended adding water, but I couldn’t check it then because it was hot, I also checked to see if I can see anything leaking but I couldn’t see any—any ideas?

Also, I cant remember off the top of my head but I want to say the last oil change was around 155,000, And they did synthetic which should last about 7500. And before I’ve Let it go almost 10,000 miles with a regular oil (non synthetic) change and I haven’t had problems

i2006 F150 XL 4.6
about 163,000 miles (?)

 

Maybe there's a vaping teenager under your hood?

Seriously though, not sure what would make white smoke, was it steam? Seems like that would be hard to miss a leak. Or burning rubber smell? I would think you'd notice that too?
Maybe you drove through a puddle right before you parked and it was just cooking off the splash water?

 

I didn’t drive through any puddles as it wasn’t raining. I didn’t notice any burning smell, I did let the engine sit overnight and did notice the coolant was really low, so I added some—hopefully that fixes it

 

Coolant doesn't just disappear, topping it off doesn't fix anything it is just a workaround until you really fix it.

Look for the coolant leak and fix that, coolant would not be low unless it was leaking.

 

if you are not careful you will blow a head gasket or motor .You have a serious coolant leak possible water pump fail . Check all your hoses could be a intake manifold leak . i'm sure you are going to need new hoses soon. .

 

Who told you that you can't add water to a hot engine? All vehicles made since the early 1970s use a coolant reservoir so you add coolant to that and not directly to the radiator. The reservoir has lines showing the max level of coolant to put in them, both when the engine is hot and when it's cold.

 

Um. No.
The coolant tank is pressurized on these trucks. If you take the lid off while its hot it will blow hot coolant out the lid. Don't open it while it's hot.

 

I added coolant to the reservoir, I seemed fine for about 2 weeks but I went to the gas station yesterday and it was doing it again...and I did notice a burning rubber smell

 

you better get that coolant system pressure tested. or get your own from harbor freight.