I noticed that my '03 had 7500 mile oil changes but my new '04 requires it every 5000 miles. Why the change if it's the same engine?

 

the answer is due to the ULEV and the elevated cylinder head temps. the oil will break down quicker and Lexus (Toyota) knows this, if the oil gets cooked too long ie;7500 miles vs 5000 miles, there will be a "chance" that you will start to get oil build up or "coking". Hope this helps!

 

It also depends on your driving habits. I just came back from a 5,000 mile trip to Florida. The oil is fine (Mobil 1 5-30). Driving highway miles is like getting the oil well done. Driving city miles for the same distance is likely getting something cooked rare, thus causing gelling. Still wise to change anyway.