1989 f250 hd automatic "460" engine. Recently purchased and right away mpg 7 and only have rear tank with around 150 miles per tank. Uses a gallon of oil in between fills. Truck does run great but loud as hell. Ordered exhaust manifold gaskets and bolt set. Installing tomorrow. I removed the air cleaner and two air duct to the upper intake in the back and filtered it at that point. The mpg increased immediately from150 a tank to 237 on 87 octane. Premium 92 got worse mpg.
the oil consumption is nothing I've ever encountered, but it doesn't smoke; however, when I got on it on the freeway, it did smoke then stopped. Here's my question. Any info or experience dealing with this and second when I put the new exhaust manifold gaskets on, I'll be inspecting each port for the blow by to identify valve seals. Finally, without removing the heads, I want to replace the guides with the best possible method that isn't going to create a head ache. (Pull spark plug bring cyl up to tdc use air keeping the valves up or was thinking I can use one of my 5 gal bucket paint filters to put in the cylinder head accompanied by a screw driver supporting the valves from falling in. Any assistance greatly appreciated
Thanks

 

First things first. Do a compression check. There's no point is replacing valves if your rings are toast.
then pull the valve covers and inspect inside your valve springs to ensure your umbrella seals haven't fallen apart.
Good luck. I think you'll need to yank the heads to replace the guides properly.