Car Starts In Cold Weather, But Not In Hot Weather

March 6, 2010/Auto By Line


Dear Doctor: I read your column every week and I hope that you can help me. I own a 1991 Honda Accord four-cylinder with the automatic transmission with the (S) button on the shifter, which I never use. The car has 105,000 miles. In cold weather the car starts up without any hesitation. In warm or hot weather the car cranks, but won’t start and the S light comes on. I have taken the car to three mechanics and they can’t seem to find the problem. Chad
Dear Chad: The most common fault we find with the Accord and the S light illuminating is the engine coolant sensor sending a faulty signal to the computer. There could also be a dirty ground connection on the thermostat housing. A qualified technician should check for trouble fault codes stored in the computer.
Dear Doctor: I have a 2001 Volkswagen Jetta with the four-cylinder engine. Each year when it is time to pass a smog test I must first clear all codes and drive the car at 60 mph for about 35 miles to re-set the monitors. The car will then pass inspection. I have replaced the CAT, oxygen sensors (2) thermostat and sending unit for the cooling system. After a period of time the “check engine” light will come back on with a code indicating a CAT airflow problem and a temperature problem. The car runs perfectly and the temperature gauge shows a normal warm-up time and the operation at a normal temperature. I believe the computer needs to be re-programmed, but VW says no. What is your opinion? Tom
Dear Tom: The “check engine” light illuminating after the codes are cleared and the drive cycle is completed with 2 fault codes means something is wrong. I have replaced many thermostats in these cars. When it comes to a catalytic converter failure make sure the engine is running fully at 100 percent. An engine that is not at 100 percent can cause a false code. If you did have a faulty converter and replaced it with a cheap aftermarket converter, then it may not be able to provide the correct clean up of the exhaust. The rear oxygen sensor monitors the catalytic converter on the majority of vehicles. The technician can connect a professional scan tool and actually monitor the oxygen sensors and the actual engine coolant temperature.
Dear Doctor: I have a 1998 Lincoln Continental with 120,000 miles. I have no heat. It’s blowing very cold air. This happened last year, too, and I was told to change the overflow cap, bleed the system. It worked great. When it happened again this year I did the same thing, but I didn’t get lucky this time. Could there still be air in the system? Dan
Dear Dan: Check the coolant with the engine off and cold. You can actually have the front of the car sitting higher like on a driveway apron.

Get the engine up to operating. Check the temperature of both heater hoses. If they are both warm, then coolant is flowing through the heater core, but if one is cold, then there is a blockage in the heater system. Your car has an electronically controlled heater system. There are sensors and an electric blend door motor known to fail. The technician may even be able to retrieve trouble fault codes.
Dear Doctor: I own a 2007 Mazda3 with the 2.3-liter and five-speed manual with about 35,000 miles. I have some interest in the removal of the balance shaft from the engine as a way to gain some (about 4-horsepower). Aside from what may be perceived to be the positives of this modification, what are the negative parts of this change? Will the car break down without this part, or will it continue to function properly? Is this a smart type of modification? Mike
Dear Mike: Removal of the balance shaft belt can add a small amount of horsepower gain, however, I do not recommend it. This practice is used on racecars, not streetcars. The purpose of the balance shaft is to equal out engine harmonics and vibration at 2,000 rpm and over. The long-term impact is negative on street driven vehicles. A low restriction exhaust and fresh air intake system are better choices.
Dear Doctor: I am interested in the new Ford Fusion Hybrid. Can you tell me anything about it? Have you had the opportunity to drive it? Mel
Dear Mel: I recently spent a week in the Fusion Hybrid. Our test car had over 15,000 test miles. There were no rattles or suspension noises. A close look at the driver’s seat showed no wear or wrinkles in the firm leather seat. This indicates good quality leather. Under full acceleration the engine was quiet. I would suggest you take a good close look at this vehicle and a long road test evaluation. — Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

E-mail questions to [email protected]

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

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Copyright, Motor Matters, 2010

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