Q: I own a 2002 Isuzu Trooper and it has been a great SUV. It has 164,000 miles and I would like to get something with a little more luxury. I need 4x4 drive and usually buy vehicles two to four years old. I like truck-based SUVs. What would you recommend as a replacement? I love the looks of the Range Rover, but would not buy one due to reliability issues and cost of repairs. I was thinking of the newer Lexus LX570 or Toyota Land Cruiser, but really don't need a V8 and full-time all-wheel drive. All the domestic truck-based SUVs seem either too large or too small.  A: Two vehicles come to mind: the Toyota 4Runner and Nissan Pathfinder. Both are midsize truck-based SUVs that are available in luxurious versions that cost about $40,000. The Ford Explorer is another to consider though I think the 4Runner and Pathfinder are nicer.  Q: I am interested in the 4-cylinder Sienna 2011. I have a 2005 6 cylinder Sienna with 60,000 miles and love it but need a second car for the weekend when the children have activities at the same time in different places. Do you have any feedback on the 4 cylinder?  A: I haven't driven the four-cylinder Sienna, but I can imagine how it drives. I recently test-drove a four-cylinder version of the Buick LaCrosse. The large sedan's engine was similar in size and power to the one under the Sienna's hood. The four-cylinder engine works well in the Buick, though acceleration can be a little sluggish. In a vehicle as large and heavy as the Sienna I think the four-cylinder's performance might disappoint some drivers. It's worth a test drive, though, because the four is likely to give you significantly better real-world fuel economy.  Q: I would like to purchase a 2011 VW Touareg or Audi Q7 in the fall. Both of these vehicles get very poor miles per gallon with the gasoline-engine versions. The Diesel versions get much better mpg. I do not know much about diesel engines other than better mpg. How does the cost of maintaining a diesel engine compare to a gasoline engine?  A: Fuel economy for diesel SUVs typically is several miles per gallon better than for their gasoline-powered counterparts.  But diesels have gotten more complicated in the past decade or so, with high-pressure fuel injection systems and sophisticated engine-control electronics. They won't "run forever" the way older diesels seemed to. However, their maintenance needs aren't necessarily any more demanding than gasoline vehicles.  Q: I have a 2000 Porsche Boxster with 23,000 miles on it. I drive it only about 2,000 miles a year. I was told that Porsche says to change the oil every three months—that seems a bit too often. What do you recommend for a car that is just exercised, not driven in harsh conditions?  A: Porsche cars have very long oil-change intervals. I recall test-driving a 1999 Boxster that could go 15,000 miles between oil changes, according to its owner's manual. Since you don't drive your Boxster very much each year you will wind up making the change after fewer miles. But every three months is too often to change it. I think you can go a year or two between changes.  Write to Jonathan Welsh at mecar
Jonathan Welsh answers readers' questions on finding a new 4x4, how a 4 cylinder drives and the benefits of diesel.