I Have a strange issue with my 02 Civic 1.7L, I'm getting only 1-2 bars from cold on the temp gauge on the Highway, Minimal heat out of the blower, Replaced the Thermostat, No change. If the car idles I'll get full heat, Cooling fans come on too. But if I hop on the highway the temp slowly drops back to C. If I put the blower on High same, temp drops.

Any idea what I can check next?
Btw Water pump is 3 years old.

Ron