Shifting Not an Idle Move
Question: Why is it that allowing an automatic transmission to remain engaged at a stop light causes less wear and tear than shifting into neutral while waiting for the light to change?--J.F.S.
Answer: The shift lever is not intended to be a clutch. The automatic transmission has a clutch of its own, which is called the torque converter. At idle, the torque converter does not transfer engine motion to the transmission.
In simple terms, the torque converter operates by having two propellers inside a high-pressure oil chamber. At driving speed, the engine propeller transfers power through the motion of the surrounding oil to the transmission propeller. But at idle, the motion of the fluid is not great enough to transfer any power.
If you constantly shift the transmission between neutral and drive, you are causing a lot of wear on the transmission-valve body that controls the transmission through high-pressure hydraulic fluid.
Q: Is it harmful to alternate oil weight from change to change, such as from 10W-40 in January with no filter change to 30W in June with a filter change?--G.M.S.
A: You would probably not harm your engine, but you may be defeating the specific properties of the oil specification you have chosen.
The use of 30-weight oil in the summer is appropriate for many cars. But when you drain the oil in January without a filter change and put in 10W-40 oil, you have essentially mixed three (or four quarts) of 10W-40 oil and the one old quart of 30 still inside the old filter.
Once again, you will probably not damage the engine, but some of the oil will behave as 30 weight and some of it as a multiweight oil. It’s not the best way to go. If you want to change oil weight at an oil change, you should change the filter.
In addition, you also may be somewhat confused about oil designations. A 30-weight oil almost never carries a W designation. A W indicates that the oil was refined for winter use.
A 20-weight oil can be designated 20W-20, which means it has the viscosity properties of a 20-weight oil, but contains additives that make it appropriate for winter use.
Q: I have a 1985 Toyota Camry. The front disc brakes have started to squeal when I apply them cold. It was not that way until I had about 5,000 miles on the car. The dealer says it is caused by brake-pad dust on the rotor, and all he offers is to blow the dust off, which solves the problem for about four hours. I think there must be a permanent solution.--D.H.W.
A: Unfortunately, there is no solution with the existing brake pads on the car. Humidity, outdoor temperature and the severity of braking are all factors that contribute to the squeal, but the biggest contributor is the composition of the brake pads.
Toyota uses a “heavy duty organic” pad on the Camry, which contains some metal flakes and some asbestos. It’s a fairly hard pad, which means it will give you long brake life and a tendency to squeal. The squealing is caused by vibration between the hard pad on the rotor when you apply the brakes.
The next time you have a brake job, you might inquire about new brake pads that would have a composition different from the original-equipment pad. Other brake manufacturers may be offering alternative pads to the after-market through independent auto-supply stores.
