08 GT from new. 270,000 miles. Original cats. No codes, no issues. Do they stay or do they go?

 

Keep 'em!

 

What he said. Unless you're having ***** trouble , my advice is to keep the existing cats.

 

Love ***** trouble!

 

They are no longer providing any benefit, all the catalyst has been used up. If you're not getting any trouble codes, might as well keep 'em for legal compliance (depending on where you live). If you're a greenie and are worried about polluting (you picked the wrong car, but...), replace them with a CARB compliant CATs.

 

'08 uses full monitoring of HO2S sensors, and I suspect if the catalyst was "used up", all kinds of dopey codes would be thrown. imp

 

If the cats weren't functioning correctly, the downstream O2 sensors would have triggered a code.

 

I'm just saying... I've seen the tailpipe emissions readings of a well tuned car without any cats, and a well maintained 10 year old vehicle with stock cats. The car with cats did not have the cleaner emissions. Also, there is a reason that the warranty on the cats, while longer than the powertrain warranty, ends before the 8th year.

 

We're the NOx emissions also measured or was it only the HC and CO?

 

That's neither here not there.

At best, it says that it's possible at that particular moment for a single car without cats to meet test standards for which the mfrs have had to go to cats in order to guarantee meeting them long term for the entire fleet.


Warranty lengths - or on the flip side, component design to reliably exceed some specified warranty period by "X" amount - is determined by the mfr's desire to minimize warranty expense.

This is most likely some bell curve/statistical thing, where the warranty length corresponds to some number of standard deviations on the low side from some estimated mean time to the inability to pass testing. As a crude example, at 3 standard deviations, you'd have to plan on having to replace converter(s) on about 150 out of every 100,000 cars. Plus probably a few more than that due to damage caused by other emissions-related failures.

Which (especially for OP) says nothing about how long any cats that have lived as long as his have might still be good for. They might be good for nine more years and another quarter million miles, or they might die over the next couple of weeks.


Norm