Q. 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. 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.”

Tom Jacopi,

San Jose, Calif.

A. 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.

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. Recheck 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.

Brad Bergholdt teaches automotive technology at Evergreen Valley College in San Jose, Calif.

E-mail him at under-the-hoodjuno.com or write to him in care of Drive, Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. He cannot make personal replies.)

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AP-NY-01-14-05 0617EST