I just bought a used 99 f350 with a 7.3 powerstroke 136,600 miles and it's went thru appx. 5 quarts of oil in the 600 miles that I've driven it. anyone guess's on what to look for. also the heat doesnt work the blower does but just cold air comes out. (could the problems be related?). thanks.

Take it back. That's burning way to much oil. Someone prolly bombed it blew it up and sold it. I'd get rid of it.

The oil has to be leaking some place. Take a peak around the valve covers for oil as the turbo bolts are known to strip out on the 99 Powerstrokes. My very late 6/99 built was leaking a quart every 700 miles at 55K miles and the turbo was redone due to the bolt issue.

Now at 188K on the F series there is no turbo leaking oil issues and the 00 X at 140K uses little oil.

BTW, the heater/AC. problem is not related to your oil issue. You may have a faulty swtich or control.

Several ways to lose oil. Turbo pedestal, pan gasket, valve covers. Blue smoke is injector -O rings. If your burning oil the first place to check is injector-O rings.

Do you use an oil like Rotella? Could be possible someone put in the wrong oil just to be cheap when they sold the truck.