Torque Converter unlocked when cold.

[fawalley]

Hi all. Have a 98 Civic EX which runs great. I have noticed however that now that it has gotten colder outside it takes longer for the torque converter to lock up. I'm a 1/2 mile from the highway so pretty much I'm right on it. I can feel the 4 main shift points and usually when it's warm feel the lockup within 5 miles. Now with the cold it may take 15 miles or more. When locked my rpm at 70 is just under 3000 rpm. When not, it's just over. I'd say maybe a 500 or 600 difference.

So, here is my question, does the engine coolant sensor control the torque converter lockup or is there a sensor at the transmission and where? Thanks to any and all that may answer.

[fawalley]

Found it. The Torque Converter will not lock up until the engine coolant reaches a temperature of 170* Even though I was getting good heat, or so I thought, I hooked up a scan tool to the OBDII connecter and found that the engine was running at 155* to 160*. Went down to the auto store bought a 195* thermostat and put it in. Took no time at all for the car to get to 170* and now the heat just blows you out of the cab. The proof in the pudding was the next morning at 4 am going to work.

At 4 am air temperature was 26*. Engine coolant 30* at start-up. 1/2 mile ride to the highway and by the time I got to the 2nd exit about 2 miles away. I was already up to and above 170* and the converter was locked giving me back my fuel economy. Engine temp ran around 208* while cruising and 214* under a load.