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Q I have a 2007 Taurus with 100,000 miles on it. The manual recommends changing the antifreeze at 100,000 miles. Based on my previous experience, I am planning on changing the water pump and antifreeze at the same time. What is your opinion of changing water pumps before they fail?

A Most failures on externally mounted, belt-driven water pumps are not sudden or instantaneous. Often, coolant will begin dripping from the pump's "weep hole," a small opening in the water pump housing. The impeller shaft bearings are protected from coolant by seals, so if coolant begins to seep from this hole, coolant has to be getting into the bearings, which will eventually lead to pump failure. If this type of pump isn't weeping any coolant, I see no reason to replace it during routine cooling system service.

On engines that require removal of the timing belt to gain access to the water pump, there is some merit in replacing the pump during routine timing belt replacement to avoid paying for the same labor costs at a later date.

By the way, my recommendation for routine cooling system service -- flush and refill with fresh coolant -- is three years or 50,000 miles regardless of type of coolant. It's cheap insurance against cooling system corrosion and premature failure of expensive parts like water pumps, cylinder head gaskets, radiators and the like.

Q I recently bought a 2002 Subaru Outback with a 2.5-liter engine for my daughter to use while she is attending school in another state. According to the maintenance schedule for this vehicle, the timing belt should be replaced every 105,000 miles or after 105 months, whichever comes first. The 105 months is coming up soon but the car has only 58,500 miles on it. Several repair shops said to wait until 105,000 miles and to disregard the 105 months. Can we safely run this car until it reaches 105,000 miles before changing the timing belt, or should I change it now?

A According to my Alldata automotive database, here's Subaru's specific recommendation for this "interference" engine, meaning that if the timing belt breaks the engine can suffer major damage: "On models prior to 1999 replace every 60,000 miles. On 1999 & later models inspect every 30,000 miles or 30 months, then replace at 105,000 miles or 105 month intervals." Thus, if this were the vehicle my young son or daughter would be driving while living some distance away and we planned to keep the vehicle for several years, I would have the timing belt replaced now to avoid tears later.

Q I have a 2005 Toyota Tacoma tuck with 115,000 miles on it. At 30,000 miles I had a problem with the drive shaft. When at a stop, I felt something from the rear like someone had just bumped into me from behind. The dealer replaced the drive shaft under warranty. Now I am experiencing the same problem again. Does Toyota have an obligation to fix this problem even though the truck is no longer under warranty?

A The most common cause for this "bump" characteristic in the driveline is the drive shaft slip yoke binding on the transmission output shaft splines. Cleaning and relubricating these splines with molybdenum disulfide grease often eliminates the symptom. Another possible cause is a worn U-joint on the drive shaft. I found no Toyota service bulletins dealing with this problem, so at this age and mileage I don't see this as a warranty issue, but it never hurts to ask.