Gen-II with 80k, too old for synthetic ?

Hmmm. I never thought about this. My 2005 Prius has 170,000 miles and I use synthetic. I bought it with 119,000 miles on it and I don't know what the previous owner used but I've been using synthetic since I bought it.

I'm down about a quart every 5,000 to 7,000 miles. There are no leaks and I just had an emissions test. I can't figure out where it's going.

 

When there are no external leaks then it's always exiting through the combustion chamber (aka getting burnt). The 3 most common routes are:

1. Past the rings.
2. Past the valve guides.
3. Through the crankcase ventilation system (PCV valve).

One quart in 5000 to 7000 miles is really no big deal on an engine with 170,000 miles on it. Just make sure you check the dipstick on a regular schedule and keep it topped up but never over full and you'll be fine. Burning oil at those slight levels wont cause any emission problems.

 

Good to know. I did change my PCV valve at 124,000 miles and I know that up to 140,000 I wasn't leaking any oil. Is it possible to develop a quart loss of oil between oil changes in 30,000 miles?

 

I didn't even think about that. I really have no idea!

 

I bought an '05 with ~110K miles on it for my wife and switched to synthetic. No oil consumption or leaks that I can detect. Current miles is ~143k.

 

Yes and no. It has to go through emission 'testing'. But they don't do dyno testing anymore in NJ, they just plug into the computer and check for codes. As long as the CEL works and isn't on, you should be OK.

 

Yes.

It's often caused by some significant wear event, like running low on oil, or running with a very badly out of specification oil, or even badly overheating the engine. But lets assume nothing like that has happened to your engine.

You can also get a change in consumption when you change the oil type and maintenance schedule. It doesn't necessarily mean anything bad has happened. Surprisingly a very clean engine (internally) can sometimes use more oil than a slightly sludged up one. Apart from the oil control rings of course, where if they're gummed up you're going to use more oil, but other places like valve guides you can actually lose more oil if the engine is clean. This isn't really a bad thing in terms of future engine wear, it means that more oil is getting more freely to more places in the engine, and if a little bit of oil consumption is the result well so be it.

One quart every 5000 to 7000 miles is not something to worry about too much on an engine with that many miles, especially if it's not rapidly increasing or anything.

BTW What brand/type/weight oil are you using and what's your oil change interval?

 

Uh-oh. This may be the cause. About 10,000 miles ago my red triangle (I think that's what it was) would flash in predictable situations. Mostly hard braking to my left and going down a hill. I couldn't figure it out for the life of me.

After I thought about it for a week or so, the only thing that made sense was the oil. I pulled the dipstick and there was just a touch of oil on the bottom of the dipstick! But, something had to drop the oil in the first place.

Mobil One synthetic and here could be the other problem - 10K mile intervals.

Maybe I should change it every 5,000 miles and use regular oil?

 

If you go back to regular oil you will be doing two complete refills in 10,000 miles with an oil that does not protect the engine from ware as well as synthetic, and you may even have to top that up. Stay with synthetic and top off when needed. Check your oil at every fill up "not when the light starts flashing" it only takes two minutes and may just save the engine from a big bang and your wallet as well.