Q: I have a 2008 Corvette C6 with 44,000 miles. It continues to be a trouble-free delight to drive. My only concern is that when I turn to the left or right sharply at slow speeds, I hear a clunk, clunk clunk coming from the lower rear of the car. Any comments or concerns?
A: Since I had an '07 C6 that developed the same symptoms, this is an easy answer. The rear hub nuts have loosened up. My ALLDATA database pulled up GM bulletin No. 08-04-20-003 from June 2008 which describes how to check for proper torque on the rear axle hub nuts.
These special nuts are initially torqued to 118 foot-pounds and are designed to flatten over time and mileage to 75 ft./pds. To check for proper torque, remove the wheel center cap and apply a torque wrench to the nut. If the nut does not move at 75 ft/pds, it is properly torqued. If it does move at this torque, replace the nuts, utilizing a special thread-locking material.
Q: I have a 2013 Toyota Prius and would like to put on a trailer hitch just for a bicycle rack. The owner's manual says this is not allowed, even for just a bicycle rack. Yet I have seen other Priuses with trailer hitches. The design of the rear of the car makes it difficult to add a different type of bicycle carrier. I have talked to the dealer and written the company and haven't got an explanation as to why. Are they being overly cautious? If I had it installed properly, would it be fine as long as I meet certain criteria for use of the trailer hitch? Could you also tell me what the installer needs to be careful about so that I can make sure I get a person who understands the problem?
A: No question, many Prius owners have had some type of hitch installed to carry bicycles. I don't know the specific reason Toyota does not approve of any trailer hitch, but likely factors are structural integrity of towing a trailer, fuel mileage and the dangers of improper installation. In addition, the extra burden of towing may overstress the hybrid power system. Oh, yes, and liability.
With that said, a quick online check identified a number of hitches from reputable manufacturers specifically designed for the Prius. I would suggest checking with several professional hitch installers in your area for their recommendations.
Q: I have recently acquired a 1998 BMW 328i with 128,000 miles and have now unwittingly entered the oil and gas religious wars with everyone seemingly having a different opinion. The previous owner used premium gas and Mobil 1 10W30 oil. The owner's manual says to use 89 AKI minimum gas. I have been experimenting with 89 and 91 octane gas and so far I cannot detect a difference in performance. I plan to keep track of the mileage I get with each type gas and see if there is a difference. For oil, the manual says 5W30 in winter and 15W40 in summer. I am leaning toward Castrol Edge 10W40 since I want to stay with a synthetic. Care to add your advice to the plethora of information out there?
A: Having owned, driven and loved a handful of BMWs over the years I can share my personal recommendations. Middle-octane gasoline always provided good performance and fuel mileage with no issues. The U.S. AKI (anti-knock index) is calculated by adding the RON (research octane number) and MON (motor octane number) together and dividing by two. Europe and Japan use the RON, so the 89 to 90 middle-octane gasoline in the U.S. is closer to their premium gasolines. Our AKI rating is roughly 95 percent of their RON rating, meaning 89 AKI gasoline is the right choice for your BMW.
I simplified my oil choice by using a full synthetic 5W50 year-round.
Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.
