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Discussion Starter #1 (Edited)
My '07 w/ 111k miles on the odometer is doing terrible on fuel economy. I drive mostly on city roads, and I'm getting no more than 11mpg.

Potential cause #1: I've had a few throws of P0420 this winter and so replacing O2 sensors is on the radar. The sensors are original---regardless of whether or not the P0420 is a faulty sensor or a faulty cat, replacing the O2 sensors is a cheap-ish maintenance item.

Potential cause #2: I've noticed that my dashboard engine temperature gauge is potentially too low. I haven't yet connected an OBD2 reader to see the actual engine temperatures. Regardless, I've seen other posts on here saying that their dashboard engine temperature gauge during normal operation (ie fully warmed up) hovers at about the halfway point. Mine, however, seems to hover around the 35% point during normal operation. (Where 0% is a fully cold engine and 100% is ****ed.) I'm wondering if this is a symptom of a stuck-open thermostat, which would contribute to poor fuel economy.

Where does your dashboard engine temperature gauge hover when your engine is fully warmed up (and not overheating)?

Edit: I should add that VCM is enabled/allowed on my van, since the opposite seems to be the norm' around here. I have a VCMTunerII ready to be installed but haven't gotten around to it.
 

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Discussion Starter #4 (Edited)
Both of your potential causes will definitely cause poor MPG. Change all four exhaust sensors and thermostat.
This is my planned course of action; I have the parts on order from Rockauto.
Where does your dashboard temp gauge hover once your engine is warmed up?


Change your thermostat and your problem will probably go away. Leave your O2 sensors alone, and they will leave you alone.
Are you implying a connection between the P0420 code and the lower engine temperature? If yes, can you elaborate?
Where does your dashboard temp gauge hover once your engine is warmed up?


Thanks all
 

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If it's not reading in the middle, the thermostat is bad. The temperature gauge doesn't start moving until the engine has reach 50°C.
 

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If I remember correctly, my temp gauge is a bit below the mid point. You should have a obdc reader and a phone app like torq. Very inexpensive and it will give you info on cel and operating parameters, like engine temp.
 
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