1991 F-150 started blowing white smoke
 

Ok so I was coming back from the store yesterday and I started passing this other vehicle and had to speed up to 70-75mph to do so. I noticed at 70mph my truck would start rolling white smoke out the back. As soon as I dropped below 70 though it stopped then going back to 70 resumed the smoking. Any reasons?

is oil level normal?

Yeah I just checked it and it was fine

White smoke is usually coolant burning. Has a pretty distinct smell.

Couldn't smell anything going 70mph with them windows down. That's what getting me. White smoke at 70mph is all I have to go off of

Do a pressure test on you coolant system, could be a blown gasket on manifold or head, or even worse, you could be cracked. It's odd that it's only happening a 70 mph, but this would indicate also that it's building pressure up. check your oil of coolant and your coolant for oil, pull your plugs and see if any of your cylinders are cleaner than the others, look at your plugs and see if any of them are white or grayish color. hopefully it's something simple and not a blown gasket.