QUESTION: I have two Jeeps, a '98 Wrangler with the 2.5L four-cylinder that has 76,000 miles and a 2000 Grand Cherokee 4.0L with 66,000 miles. I was wondering how often I should change the hoses. They all feel fine, but with the Wrangler coming up on 7 years old, I'm thinking that I should change them now. Nothing is stated in the owner's manual except "inspect."ANSWER: Cooling system malfunction is the leading cause of vehicle breakdown, and maintaining your hoses will help stack the deck in your favor. Automotive cooling system hoses are under continual attack from the inside, which makes it difficult to visually predict their health.Electrochemical degradation of the inner rubber surface occurs because the metals used in the engine, radiator and heater core react with the coolant to form a battery of sorts. Hoses begin to crack near the inner ends, more so than in the center. With the engine off and cool, try pinching/massaging each hose with your fingertips, comparing the center section to that near the ends. If ridges or grooves are felt, or additional softness is evident in one area, the hose is in definite need of replacement. The upper radiator hose is usually the first to fail, along with smaller bypass hoses, if used.Most hose manufacturers recommend renewing hoses every four years, along with the accessory drive belts. Hose durability research shows rapidly increasing failures occurring from this time onward. Being a skinflint, I usually stretch this interval by a little - OK, perhaps a lot - with frequent inspections and a roll of electrical tape in the glove box for unanticipated failures. I also snug the hose clamps every few years and keep an eye out for the slightest sign of leakage.Changing hoses? Start by collecting and recycling the drained coolant. Then perform a home-flush: Refill again with plain water, run the engine 10 minutes, let it cool, and drain again to help rid the system of most of the original coolant. Look for replacement hoses constructed of ethylene propylene rubber, which is more resistant to electrochemical degradation than earlier rubber formulas.If a hose fails to twist free of its radiator or heater core fitting, slice it with a razor knife, then peel it gently away from the potentially tender component. Clean metal component fittings of any loose material with a wire brush and apply a little dishwashing soap to the inner hose ends as necessary to help them slide easily into place. Be sure to place new or reused clamps properly. They should be located just barely past the fitting bead. Too far past can cause localized corrosion and placing the clamp on top of the bead can cut the hose. Re-check clamp tension after a couple of engine run-cycles, as the rubber relaxes slightly.Before wrapping up, let's take a look at the drive belts (with the engine off). They should be snug and free of excessive cracking or glazing. Also, wiggle any tensioning or idler pulleys, checking for excessive looseness.

QUESTION: My brother and I are both auto technicians. During a recent family gathering we began swapping stories of weird and difficult repairs we've made over the years. What was the toughest auto repair you ever made?ANSWER: It was my first day as an apprentice mechanic at my hometown Chevy dealership and it was raining cats and dogs. I'd worked there the previous month as a lube kid, and business was picking up. Elmer, the tough-as-nails dispatcher, pointed to this horrible wreck of a flatbed truck across the driveway and barked "Put an engine in it." He then added "Oh, it's too big to pull inside so you'll need to do it on your back in the driveway."Elmer was the toughest boss one could imagine. During the previous month I'd seen him hire and fire a half-dozen seemingly good mechanics and I couldn't help but wonder if I'd be next.The truck belonged to a building contractor, and was the most amazing vehicle I had ever seen. What wasn't falling off the truck was held in place with baling wire, Bondo or Romex. Everywhere the truck went, a trail of oil and smoke followed, along with some very descriptive graphics that had been added to both sides by a disgruntled ex with a spray can. I could sense the other mechanics' relief and amusement as I pried the hood open to begin my quest.For each hour it took to remove and install the replacement engine I probably spent two repairing damaged wiring, replacing broken brackets or trying to understand how this truck had possibly been driven in under its own power. I asked for help only a few times or to borrow a tool, and finally completed the job in three very wet days.I dreaded returning to the dispatch window and watching Elmer's forehead wrinkle as he tabulated my time flags on the back of the repair order. He stared at me for an uncomfortably long time, grunted and said, "Here's another one. Pick up the pace this time. Got it?"This job I dreaded more than the first. A diamond earring had been lost down the defroster grille of a Cadillac Seville. Accessing the defroster ducting and heater box was bad enough, but what if I failed to find the earring? It could be assumed I had pilfered it.Tom, the shop foreman, in a rare moment of compassion, walked by and wiggled my ankle as I lay contorted beneath the dash and said, "I think Elmer likes you, kid. Two gravy jobs your first week and you haven't cried or quit yet."I searched hard, sniffled a little and disassembled that car so far it was scary, but finally, I found it. The earring was stuck to some fuzzy sticky yuck in the back corner of the blend door housing.Things got better after that first week. After Elmer had measured my grit, and I continued to perform minor miracles each day, he turned out to be one of the nicest gentleman one could ever meet.

QUESTION: I recently had to buy two tires for my 2000 Toyota Avalon. I bought them at a Costco in Southern California, and they were filled with nitrogen. Could you please explain the pros and cons of this practice and what to do if you get a flat?ANSWER: Nitrogen has been used to fill the tires of aircraft, trucks, military and off-road vehicles and race cars for some time. A growing number of tire retailers are now recommending nitrogen for passenger-car and light-truck tire inflation and have purchased nitrogen generators, at a cost of approximately $5,000 and up.This dry inert gas has several advantages over air - except it isn't free. The main benefit of using nitrogen to fill your tires is to better stabilize tire-inflation pressure, which improves tire life and vehicle handling, in addition to providing greater safety. Nitrogen seeps more slowly through a tire's casing and contains virtually no moisture, which can cause pressure fluctuations at higher temperatures.According to one tire manufacturer, a typical tire inflated with compressed air might lose 2.7 pounds of pressure monthly, while one filled with nitrogen loses 0.7 pounds.Additional claims by the pro-nitrogen crowd are the elimination of wheel rusting or corrosion and internal tire degradation due to oxidation. This part seems to me to be a bit of a stretch, as rusted/corroded wheels aren't much of a problem, and the outside of the tire is still exposed to air. One also should note that the compressed air most of us are currently using already consists of 78 percent nitrogen.Is nitrogen worth the $2 to $5 a tire some shops charge to fill them? If you own a tipsy or heavily loaded sport-utility vehicle, or a performance-oriented car with expensive alloy wheels and tires, probably. If you drive a typical vehicle and check your tires regularly, as we all should, switching to nitrogen is unnecessary.To answer your final question, one can add compressed air to a tire containing nitrogen. That's good, since there are limited places in which to find nitrogen. There are no additional safety concerns related to servicing a tire containing nitrogen.Let's finish with a little more information on tire inflation. A government study estimates that 2 million gallons of fuel are wasted each day in the United States because of underinflated tires. Underinflated tires also are the leading cause of tire failure, and improper inflation (over or under) can adversely affect vehicle braking and handling.Tire pressure should be checked when cold, going by the vehicle manufacturer's specification listed on the driver's door or pillar sticker, rather than the maximum inflation value listed on the tire. Accelerated wear in the center of the tread indicates previous overinflation, while increased wear at both outer edges may be caused by underinflation.Brad Bergholdt teaches automotive technology at Evergreen Valley College in San Jose, Calif.