Dear Doctor: I own a 2007 Honda Civic. The manual says to use 5-20 HD motor oil. I went to the auto parts store and found 5w20 oil; however, it did not have the HD letters. Will this oil meet the factory specs? -- Gary

Dear Gary: Today there are many different oil designations. The letters HD in the oil industry can indicate different meanings for each oil company. You can interpret it as heavy duty or high detergent. As long as it is high quality oil and has the API logo and meets the oil spec designation required by the vehicle manufacturer, you are safe. Look on the oil container for the rating and compare it to the rating in your manual. As of now, the SM rating is the highest.

Dear Doctor: I own a 1998 Mazda 626. The car hesitates from a stop when I try to accelerate; it also runs rough on the highway. The computer shows nothing when I take it in for service. -- Cheryl

Dear Cheryl: Whenever I get a complaint like yours, my first step is to drive the vehicle to confirm the problem. Then I'll hook up a scan tool, fuel pressure gauge and take it out for a road test. I require that information before attempting replacement of parts. The hesitation you describe can be caused from low fuel pressure, early EGR valve operation, weak spark, lazy throttle position sensor or idle speed motor.

Dear Doctor: I purchased a new Ford Taurus wagon in 2004. Shortly after delivery, I felt a rapid vibration in the gas pedal. I took the car to the dealer and they repaired it. Now 20,000 miles later, the same feeling is back again. What can cause this? -- John

Dear John: In order for you to feel vibration coming from the gas pedal, there has to be a mechanical contact between the gas pedal assembly, cable or throttle body. Start with an inspection at the throttle body and work back to the gas pedal bracket assembly under the dash. Go back to the Ford dealer and ask for a copy of the previous repair.

Dear Doctor: I recently purchased a new Toyota Prius. I live in California and am able to drive on the high occupancy lane because it's a hybrid vehicle. Is there any problem with getting right onto the highway without the engine being warmed up first? Bob

Dear Bob: With any vehicle, it is always best to drive at a moderate speed until the engine has a chance to warm. I recommend letting the engine idle anywhere from one minute with temperatures 40-plus degrees Fahrenheit, to three minutes below 40 degrees.

Dear Doctor: I own a 1992 VW Cabriolet. For about a year the car has been bucking, lurching and losing power. The recent repairs are to ignition switch and harness, plus a tune-up including distributor replacement. The battery failed and was replaced. Could the battery have been the problem? Could a failing battery be kept alive by daily driving? Daniel

Dear Daniel: Let's start with the battery question. A weak battery will cause the electronics of any fuel-injected vehicle to misbehave. A weak battery can start the engine and be kept alive with daily driving until it has total failure. Fact: One out of four vehicles on the road need a battery replacement. Back to your bucking condition: I suggest someone hook up the proper test equipment and get the car on a road test with the equipment connected. I have replaced a lot of fuel injectors on a variety of vehicles. I have seen many technicians overlook partly blocked fuel injectors.

Dear Doctor: Lately, the gas mileage in both of my vehicles has decreased. Are the oil companies playing around with the gasoline? Jerry

Dear Jerry: The gasoline formula changed in the fall for the cold weather. The gasoline blend is changed for easier starting, especially when the temperature drops below 40 degrees. Also, engines are operating under less than ideal conditions; headlights and heat are on, as well as the electronic rear window defroster. In some cases we may let the engine warm up before driving away. The oil is also thicker when cold, which robs fuel economy. Switch over to full synthetic oil and then monitor your mileage in both vehicles. Think spring, it is only a few months away.

Send questions to: Auto Doctor, 3 Court Circle, Lakeville, MA 02347