Article taken from Auto service and maintenance advice from TCC
Q--My Mercury Grand Marquis was purchased new on July 1, 1996. I was targeting July 1, 2005 for turning 500,000 miles. I lightened up on my driving the past six months since the price of gas increased so I will not make the target date. However, as of today I have 487,000 miles on this auto, with the original engine (the only engine work was the replacement of intake manifold) and no transmission work, nor any exhaust system service. I change the oil and oil filter every 3000 miles, and never run oil low. My car currently burns one quart between oil changes. I change air filters every fourth oil change, spark plugs once per year (about every 55,000 miles), and change transmission fluid every 100,000 miles. My car continues to average 22 to 25 mpg with very low maintenance therefore my total cost per mile is superior to nearly every car on the road. Also, I burn only branded gasoline. I think the detergent package is better. And oh yeah, I am also under 60 years old.
A--I couldn't resist running this letter. Not only is the mileage marvelous, so is his maintenance regimen. Although letters continue to trickle in on the highest-mileage vehicle, I promise this will be the last I use, unless somebody has a million-miler.