I have an intermittent problem that is reducing our gas mileage to about 13MPG. When we first purchased the car, the mileage was 17-18 in town and 27-30 on the highway.

I live in San Francisco (the city of 100 hills) one block from the beach. I travel on a street at least five times a week that has a 2% grade. My destination is 315 feet above sea level and about 1.75 miles East of my home.

On the return trip (coming down hill), I often notice that the car is slowing somewhat. This problem does not always happen, but is fairly regular. When I travel down this street with a 35 mile speed limit and the problem is occurring, the car will increase to at least 45mph. When the problem does not occur the speed stays under 35mph. The transmission indicator shows 'D' but it feels like the transmission has downshifted. On two occasions while parking, the transmission shifted very hard and the car jerked.

I took the car to the dealer last year and they could not find any problem. Perhaps they do not have any hills nearby to test the car on. I called the dealer Service Manager recently and asked if he had heard of such a problem. While not wanting to commit himself, he thought he has heard of it.

This problem does occur when on the highway. I regularly drive on Interstate 5 North and get 27-32mpg.

Has anyone hear of this problem? If so, what should I ask the dealer to look for?

2007 Sonata SE/Limited
3.3l V6 engine
current mileage 53,000
oil changed 7/21/2010 5W20
all fluids full as of 7/21/2010
all fluids change by dealer at 30,000 miles
car is still under full warranty

 

This is a correction to my posting of November 2010. I had some information reversed.

I have an intermittent problem that is reducing our gas mileage to about 13 MPG in town. When we first purchased the car, the mileage was 17-18 in town and 27-30 on the highway.

I live in San Francisco (the city of 100 hills) one block from the beach (sea level). I travel on a street at least five times a week that has a 2% grade. My destination is 315 feet above sea level and about 1.75 miles east of my home.

On the return trip (coming down hill), I often notice that the car is slowing somewhat. This problem does not always happen, but is fairly regular. When I travel down this street (the speed limit is 35 mph) and the problem *IS* occurring, the car will maintain a speed of about 35 mph. The hill is sufficient that I do not have to use the accelerator or the brakes. It feels though as if something is slowing the vehicle.

When the problem is *NOT* occurring, the speed will increase to about 45 mph. I suppose if I did not break, the speed would go even higher. Again, I am not using the accelerator, but am using the brakes to slow the car to 35 mph. The transmission indicator shows 'D' but it feels like the transmission has downshifted slightly.

I have taken the car to the dealer twice and they could not find any problem. Perhaps they do not have any hills nearby to test the car on. I called the dealer Service Manager recently and asked if he had heard of such a problem. While not wanting to commit himself, he thought he has heard of it. I would not be surprised to learn this is a computer problem.

This problem does *NOT* occur when on the highway. I regularly drive on Interstate 5 North and get 27-32 mpg.

Has anyone hear of this problem? If so, what should I ask the dealer to look for? I am thinking of asking the dealer to take the car to a hill and drive down it a number of times. Perhaps they will be able to sense the slowing problem.

 

Sounds normal to me. Yes, there is engine braking in lower gears but not in the highest gear. My suggestion, when you feel this "problem" move the shifter to the manual gate and see what gear the trans is in. Then, the next time the "problem" is *NOT* occuring, do the same thing and see what gear it's in. My guess is the the problem happens, the trans is in a lower gear than when it doesn't happen. Again, normal.