2003 Kia Spectra cranks slowly and won't start when engine hot.

Your engine has Oil jets that spray on the cylinders. these are not working most likely sluge in the jets. Your pistons get too hot with lack of oil and expand inside the cylinders so this is going to be very expensive to fix and the damage done so far is most likely really bad. Try a engine sluge flush mix but do not drive the car just rev for a few minutes then drain and put oil back in. This may not help as the sluge from other places in the engine will get loose and may clog other stuff. By now your piston rings and pistons are so burnt up you most likely have lower than recommended compression.