My 01 Impala runs about 175 degrees normally (1/4 gauge), but in traffic it often heats up to 200 degrees (1/2 gauge). It never overheats, but when it runs at this warmer temperature, the transmission shifts harder. Manifold intake and thermostat replacement, and radiator flush have not corrected the problem. Both electric fans seem to be running fine. It has done it for the 4 years I have owned the car. Any suggestions?
The reason could be that the transmission fluid has lost its thermal properties. You should take it in to get it checked out.
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