2oo5 caravan 3.3 liter.Was getting 420 code..replaced upstream O2 sensor...no change.Checked upstream and downstream cat temps with downstream being 80 degrees cooler.Added CATACLEAN and went for 30 miles... filled tank and went for 90 mile drive.Today filled tank and found my gas mileage had increased from20 to 27 mpg!Check engine lite was still on so I erased it and will see in 2or3 days if it returns.Checked cat temps with hot engine...upstream 375 degrees downstream 300 degrees...still 75 degrees difference.Anyone know what normal cat temps should be?My GM truck is 5 degrees cooler on downstream side...

 

Hmm. I've always read cat peak efficiency is around 600 F.