00 Avalon Not shifting into O/D with no codes...

[MRAGS80]

Hello, Anyone else experiencing your Avalon not shifting into O/D on the highway but will shift into overdrive on rural roads with speed around 40-45 mph. I talked with a Toyota Tech and he advised me that Toyota's are known for this problem without tripping a code. He siad to change my thermostat and that would fix the problem. He explained that at highway speeds 65-70 mph the thermostat was not closing as it should, there for keeping the coolant temp in the 175 degree range, not warm enough to allow the trans to shift into O/D, but driving around in the 40-45 speed range the air flow through the radiator was lower, allowing the water temp to hit the higher 182 degree range which would allow the car to shift to O/D. I changed the thermostat and everything is back to normal car shifts into O/D perfectly. Side note , I've always changed my trans fluid every 5k since new with DEX III and Mobil 1 Synthetic in the engine every 10k.

Hope this helps anyone experiencing this problem.

[ChiTDI]

Haven't had this malady, but thanks for providing the info.

[brainpause]

Trans fluid every 5k miles?

Wow! You are just renting that fluid.