I've replaced the oxygen sensor unit and got the engine to run fine, but it still runs cold on the freeway only. Around town it runs at normal temp with the temp guage showing about middle area. But once I get on the freeway it cools down and I'm concerned that it may be ruining my gas milage so I'vedangled a 10" x 10" piece of cardboard in front of the radiator to allow it warm up better, and it works great. But I'm afraid this is only a temp fix and when summer gets here, I'll probably have to remove it. Any suggestions. I did check out the water thermostat and it looks like new and opens up at 180 degrees. I've heard you can buy a higher temp (195 degree) thermostat and I'm thinking about that too, but could it be caused by something else somebody may be aware of?
any comments or help much appreciated

 

Thermostat opening too early or being stuck open is the only thing that really can cause an engine to run too cold. Thermostat on your MPV should begin opening at 180'F but should not be fully open until 203'F. Would look at installing an OE one or the 195.