"High Mileage" oil or heavier weight oil?

Get the least expensive 5W30 dino oil you can find that's a major brand or national/regional store brand. If you're using five quarts between changes (5000 mile interval), that's 8.5 qts of oil. Still not that bad. Don't be tempted to just change the filter and not doing complete oil changes - you still should still do them because the additives in the oil will get depleted even though you're adding a fresh quart every 1000 miles.

Unless you can get a good deal on synthetic, switch to dino oil since it's always cheaper. I have been able to buy full synthetic for my vehicles at about $2.60 a quart recently. I also had stocked up on Pennzoil Platinum when Pennzoil was running a promotion on it a couple of years ago. I still have 20 quarts of 0w20 for my Altima and 5 qts of 5w30 for my Prius left over. That was a great deal at $1 per quart.

So, if you can buy quarts for $2 or less you will not be breaking the bank if you DIY at $17 plus a $5 oil filter every three months. It's likely that your Prius only burns oil and doesn't leak it so high mileage oil does not help you that much so don't waste money on it. It's a hassle having to add oil so frequently but as long as the oil consumption doesn't get much worse you can soldier on the way you have been.

 

Sorry to hear about that. I should have known you would have problems with the cat conv once the oil consumption got that bad. My 05 burns about 1 qt every 2500 miles so I haven't experienced it (yet). And you're in CA with rather stringent emission laws (again, something I should have considered). Oh well, as Emily Litella on SNL used to say way back in 1976..... "Never mind".

 

I would try heavier oil first, before going to "high mileage" oil. My understanding is that the latter (by design) has additives to swell seals, and if you subsequently go back to regular oil the seals will shrink and then some. In short: once you start with high mileage oil, best to stick with it.

 

I agree with the Prius mechanic. Using a thicker oil often reduces oil usage on old cars that are burning more oil than they should. The only thing to watch out for is still being able to start in the winter. However in San Diego, you're never going to have problems starting the car with a thick oil, even a 20W. Therefore I would try 10W-40 and see if it reduces your oil use. If you've already used a high mileage oil in the car, I agree with Mendel and would stick with it, just go up in oil weight. Sure it will cost you a percent or two in fuel economy, but it should save the cost in oil and extend your cat life.

At least one PC reported reduced oil use after running several cans of engine cleaner through their car, but it's unclear why this would happen.

The other thing to recognize is that high oil use is indicative of the last part of an engine's life. If the oil is leaking into the cylinders and burning it, it could point to an issue like a failing head gasket, which will likely get even worse as the car ages. Some seal(s) in the engine are failing somewhere. You'll probably turn over the 10K number on your odometer several more times, but more may be unlikely without an engine rebuild/swap. Take measures to be prepared (financially, etc.) for an eventual engine failure.

 

A failing head gasket typically allows coolant into the cylinders, not more oil.

 

I love the phrase "anti-wear additive" or sometimes they'll advertise "extra anti-wear additive."
If they really worked then people would use them on new engines before the wear happens -right?

The seal conditioners in the "high mileage" oil can sometimes help cars with a smoking or drinking problem but you don't have a seal problem. You have a ring problem.
Since there's no such thing as retroactive oil changes, I'd club up to a heavier middle of the road oil and let the Prius keep saving you money until you fod out the second CAT.
Catalytic converters are waaaaaaaaaay cheaper than car payments.

You can reduce your OCI, if that will make you feel better but you're effectively replacing your entire oil supply every 4k....so I'd keep driving it and see if the increased viscosity oil makes a difference.

Good Luck!

 

Before resolving your car to regular infusions of fresh oil, make SURE the PCV system is working correctly. If so, 10w-40 won't hurt anything in a moderate climate like you describe.

 

A clogged PCV valve will result in air pressure increase in the crankcase, pushing oil past piston rings, seals and gaskets.

 

I agree with you and ETC; failing piston rings are a more likely cause of burning oil than a gasket.

 

Or negative CCP causing oil to be pulled from the under valve cover area into the intake stream. This is REALLY common on older vehicles when the PCV valve spring wears out, breaks or melts

 

You can try the Mobil-1 5W-30 High Mileage as is formulated to be a little heavier and try top leaks...but perhaps no miracles.

Another idea, try the Mobil-1 oil filter...just got some from Amazon and they seems to have a good rating for maximum crud uptake.

Also review @chogan2 recent experience he added lots of Techron to rid some carbon off the engine. Can't recall if he saw less oil consumption.