Q: Recently on a road trip I was passed by a car on which one of its rear tires appeared to be bouncing up and down. A few miles up the road, it was stopped. That tire had blown out and had taken most of the back bumper with it. What causes a tire to be vibrating like that when cruising on the interstate at 75 miles an hour?

A: An ignorant motorist. I can't imagine the driver not feeling the vibration from that wobbling tire at that speed. Unfortunately, I've seen more than enough evidence of major problems that potentially affect vehicle safety being completely ignored by the motorist - primarily because nothing had happened yet.

In this case, I would suspect two possibilities. First, a tire that has suffered a structural failure or belt separation in the carcass or a progressive separation of the tread, which could explain the rear bumper damage. Secondly, a dead shock absorber/strut on that corner of the vehicle. The uncontrolled up-and-down movement of the wheel could lead to this type of tire failure - eventually.

The moral of the story? If it doesn't look, feel, sound, smell or drive right, stop and investigate why. Not sure if anything's wrong? Have it checked out by a professional.

Q: My 2003 Highlander has a horn that sounds like the Roadrunner - "beep beep." Needless to say, I'm not given much respect when I honk at someone. They keep sliding into my lane just clear of my bumper. Is it possible to replace the original equipment horn with a Cadillac horn, the kind that sounds like a freight train?

A: And you think a louder horn is going to stop other vehicles from cutting you off? Believe it or not, Toyota has a fix for this. My Alldata automotive database pulled up service bulletin T-SB-0207-09, dated July 2009, that describes a new horn available for vehicles whose owners experience "an abnormal or inoperative low-pitched horn." The part number is 86520-0K050.

Q: Two years ago, the state of Oregon mandated the addition of ethanol in our fuel. Since that time we have had engine trouble with our 1994 Ford van with 150,000 miles on it running rough or hesitating when accelerating. Fuel additives helped in the past but not anymore. I found a gas station that sells ethanol-free fuel, and the van appears to run normally after my first tank of ethanol-free. Are older engines just not designed to handle ethanol, or does the fuel system need a periodic cleaning from now on? When traveling, finding ethanol-free fuel could be challenging.

A: Challenging? That's an understatement. Welcome to the world of alcohol-blended motor fuels. You are not the first, nor will you be the last, motorist to experience fuel system and drivability issues when switching from pure gasoline. In Minnesota, we experienced these problems back in the '90s when ethanol was mandated in our fuel. In Florida, the same issues cropped up a couple of years ago when ethanol was added to its fuels. In these two states, non-alcohol fuels are available only from limited sources and are for use in recreational vehicles, small engines and collector vehicles - which helps those of us with older equipment and vehicles.

Alcohols are solvents. Thus the buildup over the years of moisture, varnish and other gunk in your vehicle's fuel tank is cleaned and carried through the fuel system. In addition, the lower energy content and higher volatility of alcohol may account for some of your drivability issues with your pre-OBDII engine management system. Modern vehicles are much more accommodating to these fuels.

Make sure your high-mileage engine is properly tuned - fresh spark plugs, decarbonized induction system and cylinders, new fuel filter, etc. And try ethanol fuels from different sources - hopefully you'll find one your engine is happy with.

Paul Brand, author of "How to Repair Your Car," is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: Star Tribune, 425 Portland Ave. S., Minneapolis, Minn. 55488 or via email at paulbrand@startribune.com. Please explain the problem in detail and include a daytime phone number. Because of the volume of mail, we cannot provide personal replies.