Q I have a 2005 Chevrolet Uplander van with 91,000 miles. After the van has been driven for more than 150 miles or so, the transmission apparently slips. When starting from a dead stop, the engine races a little and then the van moves with a jerk. It also jerks hard when it upshifts into each gear. It does not miss any gears and shifts at the proper engine RPM. If the van is allowed to sit overnight, the problem doesn't happen again until after about 150 miles of driving.

The transmission fluid is bright in color, has no unusual odor, and is up to the full level. The instrument panel does not indicate any failure codes. I suspect the problem existed before I bought the van at 68,000 miles. At the time of purchase an independent mechanic suggested the transmission fluid be changed, and I assume the dealer did so. What do you think?

A Remember what "assume" stands for! According to the recommended maintenance schedule, transmission fluid/filter service isn't called for until 100,000 miles under normal driving conditions. Even though the recommendation is 50,000 miles under "severe" conditions, I doubt the dealer performed this service before selling it to you with 68,000 miles on it.

I found several service bulletins in my Alldata automotive database addressing harsh first-gear starts and slippage. All point to potential problems in the transmission's hydraulic valve body. All suggest removing the valve body from the transmission for inspection and repair or replacement.

I would try an additive like Trans-Tune first.

Q I own a four-cylinder 2003 Camry. Lately, on a cold start I notice some light blue smoke emitting from the exhaust. The Toyota dealer tells me it is most likely the valve guides are worn and may need replacement which they say is quite expensive. I did put in oil additive recently and it seems to have helped a little. Do I have a serious problem?

A I don't think so. Valve guides do precisely what they describe: guide and support the intake and exhaust valves as they move rapidly up and down, opening and closing the intake and exhaust ports. After tens of thousands of miles, some wear is normal. The slightly increased clearance between the valve stem and guide can allow a tiny bit of oil to drain down the valve stem, sit on top of the valve head and then be drawn into the combustion chamber and burned upon startup -- thus the slight puff of blue smoke.

Consider it "upper cylinder lube" -- this tiny amount of oil isn't doing any harm. Unless oil consumption becomes excessive or a driveability problem develops due to fouled spark plugs, I wouldn't worry about it. Just make sure you keep the oil topped up.

Q My 2010 Ford Fusion has P225/50R17 tires. My dealer says I can upgrade these to a softer riding tire. My wife and I are both 75. What would you suggest that would still maintain our warranty?

A The standard size tire on the base model 2010 Fusion is P205/60R16. The taller sidewall, indicated by the 60 aspect ratio rather than the shorter sidewall with the 50 aspect ratio, would likely provide a somewhat softer ride. But, of course, you'd need to swap the 17-inch wheels for 16-inch wheels and ensure that the tire pressure monitoring system remained intact and functional. I would ask the dealer if they could swap your wheels and tires for a 16-inch set from another Fusion. This should not affect your warranty.

If you choose to keep your wheels, I could not find a 17-inch 60-series tire, which would be very close to the same rolling diameter. You could try a different P225/50R17 tire, but I'm not sure how much improvement in ride quality it would offer. Slightly lower tire pressure, perhaps 30 pounds per square inch, might help a little.