Burning vs leaking oil causing catalytic converter P0420?

For a few years now my 2004 Prius (now at 162k miles) has been requiring me to add oil between 5k changes. From reading these forums I now know that it's common for older Prii to burn oil, so I imagine that is what is going on. I originally brought it into the dealer to ask them to find an oil leak, and they said they found some drips around the timing cover gasket, near the right front. They said the reason I don't see oil spots on the garage floor is that it gets caught by a pan underneath. They quoted me $900 to replace the gasket, so I decided not to do it. After reading these forums I'm leaning towards not bothering since it's probably going to burn oil even if I do it.

I haven't been systematic about tracking my oil replacement, but my sense is it's about 2 quarts that I add between 5k changes. I will start tracking this more closely going forward, because...

I have started getting the P0420 catalytic converter error code (efficiency below threshold). I don't like the idea of polluting any more than necessary so I lean towards replacing the catalytic converter with an aftermarket one welded in for a few hundred if I can. For now I live in a municipality that doesn't require emissions testing, so I just use an odb2 device to clear the P0420 check engine code when it appears. I will probably move in a year or so, and likely to a place that does emissions testing so a new catalytic converter is probably in my future even if just to be a good air citizen.

But I want to make sure there isn't anything I should be doing to stop oil burning and trashing the new cat converter. I saw someone posted about adding an oil catch can, but it seems like that only catches a small portion of the oil replaced, so I'm not clear that would help much.

Is there any diagnostic or fix that can give me assurance that I've done what I should so the next catalytic converter won't get fouled by my oil consumption?

 

Yep, but if I get an aftermarket here for a few hundred, I may well have to write that off and spend $2kish for an OEM exhaust system if I go to a place that inspects emissions.

I will start using high mileage oil after I burn through the couple of quarts of mobil1 that I have left. In my last car I went to a higher oil weight; is there anything wrong with using 10w/30 instead of 5w/30 in a 2nd gen prius? I am in a 5000 foot elevation part of Arizona where it does go below freezing and we get snow buildup a few days out of the winter, but summers are quite hot.

Also, is there any conventional wisdom about how what level of oil burning leads to fouling the catalytic converter?

 

Good to know! That is a good reason to get it done soon. 20 minutes of googling hasn't turned up a reference to official policy on this though, so if anyone has a link to the law or policy where I can verify that I can bring in an aftermarket cat to CA that's not on the CA approved list, that'd be great.

 

I used to live in CA and the one time I had my Prius emission tested I'm pretty sure they did a visual inspection. I think it's supposed to be part of the procedure in CA.

Passing the Visual Part of the CA Smog Check Inspection - SmogTips.com

 

Thought I'd give an update: Tried Catclean fuel additive. The P0420 happened much more often while that quarter tank was being burned through. So it was probably doing something. Now that I'm on the full tank afterwards the light is less.

My Toyota dealer suggested MOA oil additive saying that it would clean the oil off the top of the cylinders so that the excess oil flowed back into the oil reservoir rather than getting burned up. He said it would take a few oil changes before it fully took effect. Not sure if it's helping. He also mentioned that if the car isn't using more than 1-1.5L per 750 miles, then probably not worth worrying much about. I'm using less than that for sure.

And I started using 10w-30 high mileage oil (mobil1) for my oil changes instead of 5w-30. Hopefully if there are any leaks that won't leak out as much.

So given that I think I'm doing all I can do, I'm going to go ahead and find a local muffler shop to weld in an aftermarket cat. A previous post mentioned confirmed that the Walker 16337 which is available on amazon for $245 works with the gen2. I'll see what my options are.

 

Finally ended up replacing the catalytic converters with Magnaflow parts 51205 and 51204. Local exhaust shop charged $270 for the parts and $95 for labor. Much better than the $2kish for the dealer exhaust system. Feels good to be done. Sorry priusprofit I didn't want to mess around with selling the old cats which were clearly dead.