Will shifting by hand damage an automatic?

Q My husband and I are having a disagreement. If you have an automatic transmission vehicle and manually downshift to slowdown and come to a stop and then manually shift into gear, is this good for the tranny? Please let me know what you think.

A The fact that you used the term "tranny" to identify the transmission answers the question -- you're a motorhead! So, if you and your husband ever decide to go racing, you drive and let him manage the team.

First of all, manually shifting an automatic transmission is not exceptionally hard on the unit. In fact, many carmakers today offer some type of manual control for their automatics. Examples include VW's "Tiptronic" and Chrysler's "slap stick." These electronic control systems give the driver the option of manual up/downshifting, or allowing the powertrain control module to handle the shifting chores for them in a fully automatic mode. There are several fail-safes in the system, such as automatic downshifts if you forget to do so, but from a fun factor point of view, moving the shift lever into the manual slot and bumping the lever forward to upshift and snicking it back to downshift can add measurably to the enjoyment of the driving experience. In light of today's congestion and frustration, shifting the transmission manually might help restore some of the enthusiasm for driving.

Even though your automobile might not have specific manual control mode, I'm sure it does have the conventional "PRNDL" selector, allowing you to up and downshift manually. If you enjoy doing so, by all means shift manually.

Are manual downshifts harmful to the transmission or drivetrain? The PCM won't allow a premature downshift that would over-rev the engine, but obviously, banging the shifter into the next lower gear forcing the engine to rev to high rpm isn't doing anything much good. And remember, the PCM will downshift the transmission automatically when speed or rpm drop below a specific point, or you step on the throttle to accelerate -- so the downshift is going to happen, one way or the other.

If you're downshifting at the same speed and rpm you would choose to do so with a fully manual transmission and it adds to your pleasure in driving, then by all means continue to do so. And suggest to your hubby that the two of you attend a Skip Barber performance driving school.

You'll have a great opportunity to improve your footwork and driving skills, and he'll enjoy a wonderful attitude adjustment toward driving.

Q I have a 2001 Dodge Caravan. I am having problems with the manual climate control unit. The issue I am having is that the air flow switch blows only max power or the very lowest flow of air. I went to a junkyard and bought the whole climate control unit and attempted to put in, only to have the same thing happen with the new part. Is there a resistor or fuse that might be causing the problem?

A Yes, the blower motor resistor might be at fault. This component sequentially steps down battery voltage to lower the blower speed from high down through the intermediate speeds to low. If one or more of the resistor windings are open, those individual speeds will not work. The electrical circuit for high speed blower operation bypasses the resistor block and provides direct battery voltage to the motor -- so high tends to work even when the resistor has failed.

You can test the resistor with a simple ohmmeter for continuity, and replace it yourself if it's bad. Access is simple, just remove the glove box, reach through the opening and disconnect the harness from the resistor. Two screws hold the resistor in place on the evaporator housing.

Remember, you're working in the area of the passenger side airbag, so you might decide that this is best left to a professional.

Q I have a 2001 XLS Mitsubishi Montero that will be going off powertrain warranty in April, and at that time I will have about 52,000 miles on it. The manual says to change the timing belt at 60,000, do you think I should go ahead and have this done before my warranty expires? My dealer wants $850 to put in a belt and water pump, which they say I should do since they'll have it apart. This vehicle has an interference engine which really worries me. Why do they make such engines?

A According to my Alldata automotive database, the 3-liter engine in your Mitsubishi does not require a timing belt change until 100,000 miles. There is some confusion here as it appears that Mitsubishi recommends -- but does not require! -- timing belt replacement at 60,000 miles on '98 and later vehicles sold in California, Connecticut and Massachusetts. On all '98 and later vehicles, replacement is recommended at 100,000 miles.

Some of these differences are likely attributable to laws in the states in question, so double check your owner's manual.

In reference to your question about "interference" engines, part of the answer is efficiency. Domed combustion chamber shapes, higher compression meaning smaller combustion chamber volume, and wider valve angles -- all engineered for better efficiency, performance and mileage -- can potentially allow contact between an open valve and the top of a piston. But only if the timing belt or chain should fail.

So, as long as it doesn't, they won't. That's why some carmakers recommend timing belt changes at specific intervals.