Hi Folks,

I have a 1996 Honda Civic LX 4DR Sedan with 115,000 miles that has been well maintained and serviced. About two years ago, I noticed that the car would not go into overdrive (5th) gear consistently, especially when it got colder (I live in Connecticut). I brought the car to my mechanic (a former Honda service manager with his own garage now) and he recommended changing the transmission fluid with original Honda transmission fluids. We did that and it improved for a few weeks and then when back to most times not shifting into 5th gear on the 15 minute potion of my ride to work on the highway. Once the weather got warmer, it shifted fine again. Come the winter of 2007-8 it started doing the same thing so we changed the the transmission fluid with original Honda transmission fluids. Again, it was better for about a week, then back to the same thing. Now that the warmer weather is here it's shifting okay into overdrive most of the time though on cooler mornings it wont do so until I'm about half way to work. In speaking to some people I know, they felt it might be a sensor in the transmission that is faulty, while my mechanic feels that the clearances are so tight in these transmissions that when the colder weather comes it's just enough the cause this problem. All I know, is that when 5th gear isn't working, my gas mileage goes from around 33 mpg to 25 mpg. Is there an easy way to diagnose the problem or should I just look to get a used transmission instead? Any and all thoughts, recommendations and advice would be greatly appreciated. Thanks in advance for any and all help provided.

Roger