Thread: Temperature readings pre/post cat - normal or problem?

I just used a temp gun to read my pre/post cat temperatures. Car had been driven up to operating temperature, outside temp about 80-ish, then I let it idle about 5 minutes.

Pre-cat temp was about 380-400F. Post-cat wasn't much different. Rear should be higher, right? I measured a few other places on the pipe. On the U-bend I could read 440-450F, consistently hotter than just after the cat. (Could that be because, the restriction that forces the exhaust through the smaller-diameter pipe, "concentrates" the heat so the reading is higher?)

For the record, I also have OBD code P0137, O2 sensor circuit low voltage, bank 1, sensor 2.

I wouldn't be too disappointed if the cat is dying, as it would be a legitimate reason for a downpipe and new cat.

Originally Posted by Fivefingerdeathpunch

Temps seem normal to me.

OK. As I keep reading about it, the old rule of thumb that says there should be about 100 degrees difference between front and back is just that, "old."

From http://www.aa1car.com/library/converter.htm

"In many late-model engines with multipoint fuel injection, combustion is so clean that the converter has little to do and the difference between the inlet and outlet temperature may only be 30 degrees F at 2,500 rpm - which is a lot less than the old rule of thumb that says a good converter should show at least a 100 degree F difference fore and aft at cruise. At idle, the converter in many late-model vehicles may cool off so much that there's almost no measurable difference in fore and aft temperatures. So checking exhaust temperatures fore and aft of the converter at idle and 2,500 rpm is NOT an accurate way to determine if the converter is working properly or not."