Cold Winter Means Drop in Fuel Mileage Returns

January 1, 2011/Steve Tackett

MOTOR MATTERS ASK THE AUTO DOCTOR BY JUNIOR DAMATO

Dear Doctor: I own a 2002 Ford Taurus with 41,000 miles. This year I have noticed a large drop in gas mileage for city driving. It was rated at 20-mpg city, but now I’m closer to 10 mpg. My mechanic checked the spark plugs, wires, filters and everything looks good. What is he missing? Dan
Dear Dan: Loss in gas mileage during cold winter months happens for a couple of reasons. First, the difference in the winter blend gasoline will lessen gas mileage. The winter blend is designed to fire off faster in cold temperatures. Second, the engine will run longer in the closed loop mode because of the colder engine temperature. In the closed loop mode the engine operates in the preprogrammed computer mode. The engine runs richer and the transmission will sometimes not shift into overdrive or top gear. Oxygen sensors also get lazy with mileage, which are more noticeable in the cold temperatures. Engine oil also thickens and causes more drag on the engine. This is where as switch over to full-synthetic oil can make a big difference.
Dear Doctor: I have a 1998 Chevy Cheyenne 1500 with 170,00 miles. In 2005 it started skipping and my mechanic replaced the distributor cap (which was cracked), rotor, wires and plugs. Since then I have had to replace the distributor cap five times. I went online in 2006 and the chat rooms suggested using OEM parts only. I tried that route but the cap lasted about 18 months. I don’t understand why the original cap lasted seven years and replacements last about a year. Are there any alternatives to this yearly replacement cycle? Terry
Dear Terry: Premature wearing of parts, such as the distributor cap and rotor can be caused from high resistance in spark plug wires and poor quality parts, even though you are buying the best from the parts stores. In some rare cases, a poor engine ground can also be a part of the problem. If I were working on your truck, I would replace all the ignition items with MSD brand parts, available at any performance store or online. You will find the quality of the MSD brand to be above all the other brands.
Dear Doctor: I have been to four garages and none can figure out the problems on my 2000 Chevy Tahoe.

The “check engine” light came on and the garage told me it was the 02 sensor. They replaced it, but the light is still on. Took it to another garage, and they too, replaced the o2 sensor. I then took it an electrical specialist and was told my 02 sensors are bad. I explained I had already replaced them. He told me I needed GM parts. I replaced all 4 with GM sensors and the light is on again — and now the “check 4-wheel drive” light is coming on. Got any ideas? Cathy
Dear Cathy: I see this problem often. Just because there is a trouble fault code does not mean the part is bad. The trouble code is relating to the circuit that has the problem. It could be anything from a broken wire in the harness, blown fuse, to a faulty ECM. In some cases I have seen the small electrical connector corrode or pull slightly out of the connector. I suggest you find a technician that has knowledge of the Tahoe. As for the 4×4 service light, this is often seen on GM electronic transfer cases and is not related to the oxygen sensor fault codes. The circuit will have to be checked. As for the use of only GM parts that is not true. There are many good after market brand parts on the market that meet or exceed OEM parts.
Dear Doctor: The extended warranty on my 2004 Acura TL will expire in May 2011. I’ve noticed vibrating on the steering wheel and the driver’s seat when idling. When I’m driving I don’t notice anything wrong, but when I stop, I have to take my hand off the wheel because it is uncomfortable to hold. It also vibrates when I am in neutral and reverse, but not as much. Six months ago I mention it to the service man at the dealership and he said that it would be looked at during the Timing Belt Service in May 2011, which is an expensive maintenance interval. I want to get the vibration fixed while the car is still under the warranty. Should I get the Timing Belt Service before the scheduled date to narrow down the potential problem? Kathryn
Dear Kathryn: I would recommend you take your car in now and have the technician look at the engine mounts and the fan belt driven accessories. I would also look at exhaust hangers, brackets and any shields. As for the timing belt service, that should be done replaced per recommendation of the owner’s manual, not before. — Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

E-mail questions to info@motormatters.biz

Copyright, Motor Matters, 2011

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