Q: We have a 1999 Infiniti I30 with 122,000 miles that runs well but has one issue — at highway speeds the car noticeably "jumps" or "skips" sideways slightly when going over big bumps. We have not replaced the struts or any other suspension components. The struts show no signs of leaking but two garages have suggested replacing them, given the car's mileage. No garage has pinpointed the exact cause of this behavior. When we bought the car the dealer ran the equivalent of a Carfax that did not indicate any accident history. Our boys have asked if they can use this car for a road trip to Washington, D.C., for spring break. I am concerned about them driving that distance given the handling issue described above. How would you suggest we diagnose it? Would new struts correct this? Is it worth spending $1,000-plus to put new struts on the car, given its age?

A: Your concern is valid and laudable. The typical car owner's only concern is that the vehicle starts, drives and makes it to their destination.

Unless there are significantly worn or loose suspension components — ball joints, bushings or tie rods — the shocks/struts are likely worn enough to allow the tires to momentarily lose traction, causing the car to skip or jump a bit. As the wheel/tire encounters a bump, the shock/strut is tuned to resist and dampen the upward suspension travel, literally absorbing the impact. It also dampens the downward rebound of the suspension, keeping the tire in firm contact with the pavement.

If the shock/strut fails to adequately slow/dampen the upward suspension movement, the wheel/tire effectively bounces, reducing the tire load and contact with the pavement that provides traction. This can generate the skip/jump characteristic.

At 15-plus years and 122,000 miles, the shocks/struts on this vehicle are certainly worn enough in their damping action to warrant replacement. Whether this is economically viable is perhaps the larger issue. A quick online search pulled up KYB and Monroe strut assemblies for this vehicle priced in the $60-$100 range, not including installation, so you might be able to have all four replaced for significantly less than $1,000.

Q: I am on my third Subaru and I think their "boxer" engine is a great design. Why haven't more manufacturers used this design? The only other "flat" engine I can remember is the Corvair engine. My other question has to do with fuel injection. How does "direct" fuel injection differ from the fuel injection we have had for 20-30 years?

A: Er, perhaps you need to raise your internal combustion engine horizon. Volkswagen, Porsche and Ferrari have built "boxer' horizontally opposed engines. BMW and Honda built boxer engines for motorcycles. Currently Porsche, Subaru, Continental, Lycoming and Rotax build boxer engines. By the way, the "boxer" engine was patented by Karl Benz in 1896, so it's a longstanding, successful engine design.

Conventional throttle body and multi-point port fuel injection deliver fuel into the air induction system upstream of the combustion chamber. "Direct" injection delivers fuel under high pressure directly into the combustion chamber, allowing significantly leaner fuel/air ratios for better efficiency and mileage.

Q: Back in the day I was taught to add gas line antifreeze during the coldest part of the winter. This was to absorb water so it wouldn't freeze in the bottom of the tank or the fuel line and block gas flow. Now that most gasoline is 10 to 15 percent ethanol, I'm wondering if there is still a need to add another form of alcohol to the tank.

A: Not on a regular basis. Ethanol in today's gasoline helps prevent moisture/water from building up in the fuel system, but can mix with existing water causing phase separation. However, isopropyl alcohol — typical gas line antifreeze — can remix phase-separated water and carry it through the fuel system. So adding it once at the beginning of the cold season could be useful.