My 2nd O2 sensor is bad (the one farther to the rear, the less important one?), still, yes! I think I've been getting worse gas mileage since this occurred. Is this common? Seems like it would be because it has to do with the air/fuel mixture???
Also, on cold nights, like tonight (outside temp 45 F), with the heat on low, going 50 mph or so, the engine would not reach a temp of 80 C. I kept it in third gear to try and get the engine a little warmer, but it wouldn't work? I know that the engine temps on C's do go up a bit higher than 80 when conditions prevail, but what about lower? Anyway, my question is, is this normal, and could it be related to the bad 02 sensor? Thanks GUYZ.

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)