Q: I always enjoy your columns but the one on downshifting confused me a little. We have a 2013 Toyota Corolla with 7,000 miles and a 2012 Toyota Sienna with 44,000. Both have automatic transmissions. When we bought each car the two different dealers both told me that the automatic transmission could be downshifted when braking without doing any harm and that it would help preserve the brakes. I do this whenever I see a stop sign or steep hill ahead. It always works fine and so far I see no problems with the transmission. Is it really OK to downshift automatic transmissions?

A: As I said in last week's column, downshifting to aid in braking with either a manual or automatic transmission isn't necessarily harmful, it's just unnecessary wear and tear on the transmission — one of the more expensive components on a modern automobile.

Maybe the best way to look at this is to identify the primary function of the transmission. This multi-ratio device is designed to operate the engine in its most efficient RPM range at any speed. It does not provide anything more than marginal deceleration benefit when downshifting while the vehicle is slowing.

The braking system, on the other hand, provides no benefit while accelerating but does an amazingly efficient job of slowing the vehicle, whether gently for an upcoming stop or aggressively during an emergency stop.

Every motor vehicle has five engines. The primary engine converts the energy in fuel into the heat of combustion, producing power to accelerate the vehicle. The four brakes are also engines, converting the energy of motion into heat and dissipating that heat into the atmosphere. The four brakes are far more powerful engines than the powerplant under the hood. The proof is in the simple fact the modern cars will stop much faster than they accelerate.

Amazingly, brakes are far less costly to service and replace than engines or transmissions. And interestingly, brake components, like tires, rank at the very top of vehicle safety components yet are at the lower end of vehicle maintenance costs.

To specifically answer your question, no, manually downshifting to aid deceleration isn't harmful, it just serves no purpose except in certain scenarios like long downhill descents to protect the brakes from overheating and fading. But, if it adds to your enjoyment and keeps you focused on driving, well, who am I to argue?

Q: Our second car is a 2000 Audi TT. It is garaged January through April every winter while we're in California. Just before leaving, the TT is washed and covered. A trickle charger keeps the battery going, and the gas tank is full. In past years I've always added a can of Sea Foam. Two friends, more knowledgeable about cars than I, said that this is a waste of money. Your thoughts?

A: I couldn't disagree with your friends more. Today's gasoline motor fuel is not engineered or blended for long-term storage. It is designed to be burned in a motor vehicle virtually the day it is delivered to the gas station. Stored for any significant length of time, exposure to even a small amount of water can cause ethanol-blended fuels to separate into gasoline and ethanol, potentially leading to contamination and corrosion. In addition, gasoline will oxidize over time, creating a nasty-smelling varnish-like residue.

An additive like SeaFoam in a full fuel tank is the simplest and least expensive way to ensure that the fuel doesn't deteriorate and your vehicle starts and runs properly when you wake it up after months of storage.

Leaving the fuel tank full during storage is a good policy because it minimizes the fuel's exposure to air and moisture. An automatic battery charger or maintainer that regulates charging to keep the battery properly charged is a better choice than a trickle charger that can potentially overcharge and kill the battery.