Q: My 2010 Saab 9-3 has a front-end shimmy at 65 to 75 mph. The wheels have been rotated and rebalanced a couple of times, and it still vibrates. Any suggestions?
_ L.C., Avon, Conn.
A: If you have returned to the same shop to have the wheels rotated and balanced, you may want to visit a different shop _ one with a Hunter “Road Force” wheel balancer. Unlike the majority of balancers, this one applies force against the tire tread with a drum to simulate actual driving conditions. The machine also has a device for checking the wheel for an out-of-round condition which could happen from hitting a curb. The correct weight is calculated and a laser line shows the correct attachment point.
Q: I drive about 100 miles daily and 80 percent of the time I am on the highway. When I get on the highway, I turn on the exhaust brake to assist when slow, gradual braking is necessary. I normally do not carry any loads or tow except the eight times a year when pulling our travel trailer, so most times no additional weight is added. Is using the exhaust brake beneficial in these conditions? Are any components experiencing premature wear in this process? I have 112,000 miles on the truck with original brakes and they check out at 50 percent remaining.
_ K.B., Aurora, Ill.
A: The exhaust brake, which should not be confused with the Jake Brake on big truck engines, simply creates some back-pressure making it more difficult for the pistons to move. The air that would normally flow freely on the exhaust stroke gets bottled up _ partially. Using the exhaust brake on the highway won’t hurt anything, and it won’t help anything around town. But it really helps when you have a heavy load, especially descending a hill, and saves the brakes from overheating.
Q: I have a 2014 Dodge Journey with a V-6 engine. The car has been excellent. However, when I have brought it in for oil changes, the dealer tells me that I should clean out the throttle body every 10,000 miles. I now have about 28,000 miles on it, but haven’t taken their advice, because the manual doesn’t say to do it. The dealer says the cleaning will improve mpg. During the cold weather I notice a drop in mpg, but I think it is due to longer idling periods. What is your recommendation? Should I follow the dealer advice, or just stick with the manual?
_ J.V., Chicago
A: Follow the manual. Although cleaning the throttle body may marginally increase fuel economy, it is not required maintenance. Cold weather affects fuel economy not only due to longer idling times, but greater accessory loads such as window heaters, wipers, headlights and so on. Also, until everything warms up the various lubricants (transmission, differential, wheel bearings and so on) and until they thin out, they can cause drag.