I've read that the stock thermo. is 195 on the 5.2. My question is if the engine isn't running that warm, say around 170- 175 on the gauge, wouldn't that tell the PCM that the engine isn't warm enough and make the fuel mixture richer? Just wondering if this isn't part of my MPG problem.
Any experience with different temps? I have stock PCM with the "death flash" unfortunately, and don't think that can be changed back.
Also, could an O 2 sensor, or a TPS affect fuel mileage?

 

O2 is the most common killer of mileage. TPS can affect it too.

I don't think the engine running cool would make much of a difference as far as mileage. If anything you'd have better mileage. Fuel actually works as a cooling agent. This is why you have to add fuel flow when you add nitrous, the fuel cools the combustion temperature so the nitrous doesn't melt the pistons.. If you're running too cool, a leaner mixture would bring the engine temperature up, so I doubt that's your problem.

 

By the way, you should run the codes in your PCM and see what they say. That's the easiest way to determine where to start looking for a problem.

 

plus cold fuel is good for a 6% increase in mpg... (from my own experience with a fuel cooler)... but that's off topic here, sorry

if your motor is running too cool it could be running in open loop mode which will cause it to run richer. the 180 stat is the one to pick if your gonna change it, it will lower your head temp and not heat your intake charge as much as a 195 stat before it enters the CC.

if you have the death flash, get rid of it (get a new pcm if you have to), it's contriubting to your poor performance which will affect your mpg...