PCV and Oil Consumption

I know it's a PIA to get to but just change it and see what happens.

 

Yes I would change it . It is not worth much to try. H

 

The PCV Valve produces "when it is working correctly" a partial vacuum in the sump chamber (crank case). If it is not working correctly this can and does become pressure helping to push oil up the cylinder walls. I know of no mechanism that would give a DTC error. In days gone by the crank case was vented to outside atmosphere through a wire filter but now with emission controls the gasses from the crank case are burnt in the engine.

John (Briprius)

 

At 100k miles it's good idea to change the PCV valve as preventative maintenance, so even if it doen't fix your problem it's not a total loss.

 

I had a civic with a stuck pcv valve. No lights. The only sign was excess oil consumption. Changed it with a new one and consumption was almost none. I would change it just to get rid of the curiosity of it being the pcv or not.

 

Yeah, change it. There is absolutely no reason for the ICE to be burning oil at 100,000 miles (unless it was abused). My 01 has 117,XXX miles and it loses no oil in between changes. You have to figure the ICE in a Prius only runs about 60-90% of the time (depending on driving habits/commute) so 100,000 miles = 90,000 engine miles at worst but likely less than that. Even a Chevy engine doesn't burn oil at 100,000 these days.

Was your car/ICE abused (long intervals between oil changes etc)?

 

Usually your posts are spot on but I just couldn't let this one pass by without commenting on it.

The Prius Gen 2 ICE runs 100% of the time on flat terrain at highway speed >50 mph. The Prius ICE rpm
tends to be lower than a gasoline or diesel ICE but it's still running nevertheless.

Your estimate is wayyyyyyy off.

More like 85% to 97% of the time for most people.

 

What proportion of the time is your car driven on the freeway, and what is its average freeway speed?

I live in an area where the freeway speed limit is 75 mph. I don't think it is unusual for a Prius with 100K miles logged to use 1 -2 quarts of oil between 5K mile oil changes.

 

I don't think usnavysgt is all that far off.

I agree that at freeway speed that the ICE is running most of the time, so some people doing almost exclusively freeway driving would be going more than usnavysgt's upper estimate of 90%. But equally true is that some people doing mostly low speed commuting on local roads will have ICE usage as low as 60%. So it's a pretty broad spread, perhaps 60% to 97% would be a better estimate.

 

No, the ICE is running ALL of the time at freeway speed on a Gen II !!! The Gen II has a single planetary gear set in the eCVT. Above 42 mph the ICE must run to limit the rpm of MG1. By running I mean, it's either firing or motoring (spinning without firing - aka engine braking). Most of the time the ICE will be firing, of course.

And there's practically no way anyone can achieve an ICE usage as low as 60% on a regular basis unless they hypermile their Prius. Hypermilers and the pulse and gliders want to maximize their fuel economy and MIGHT be able to get 60% ICE. But I don't consider them to be in the mainstream and fortunately they have their own websites and forums specific to their goals and interests.

In order for a Gen II Prius to achieve a 60% ICE usage, for every 10 miles of travel, that would be 4 mi. traction battery and 6 mi. ICE, right? But the Gen II can only travel about one mile solely by electric propulsion on a full charge before the ICE starts again to recharge the traction battery per the Toyota BMS which keeps the traction battery SOC in a narrow range (~40% to ~60%) to make it last 10 years.

So, the only way anyone with a Gen II Prius could drive 10 miles with the ICE running only 60% of the time on level ground the sequence of ICE to traction battery propulsion required would be 1.5 / 1 / 1.5 / 1 / 1.5 / 1 / 1.5 / 1.
I just don't see how the ICE can fully recharge the traction battery in just 1.5 miles even adding regenerative braking. Not if you drive the Gen II Prius like any other car, which is clearly what Toyota intended.

 

Yes I understand that the ICE is always turning above 42 MPH, the suggested 97% upper limit is meant to include the fact that almost everyone is going to have at least some slow speed driving getting to/from the freeway and off ramps etc.

Anyway the the 97% figure was yours, I think it represents somewhere about the maximum ICE usage for most users. The contention was about the lower figure. I'm not saying that it's most people, but some people get ICE usage as low as 60% in slow speed local road driving. If you're going to include the worst case (almost all freeway driving) then I think you should consider the best case too, which is almost all low speed local driving with some mild hypermiling techniques.

 

I agree that at freeway speed that the ICE is running most of the time.

These are the words in your previous post, uart. So either you didn't understand or you were just careless which is no biggee. ​

The best case should not include any hypermiling. That's not real world use.

The one thing I really hate is unrealistic claims and expectations about the Gen II Prius. It's a great car. But let's not make it more than what it is - it's just a hybrid - not a Nissan Leaf, a Volt, a Tesla, or a PIP.

And if I had any of those cars, I wouldn't want to drive them gingerly just to eke out a few extra mpg.

​

 

Your wording of running 97% of the time on the freeway is misleading a better term would be spinning as even at freeway speeds you take your foot of the accelerator and fuel is cut off to the engine and the valve timing is altered to allow the engine to spin freely. It is not then running.

John (Britprius)

 

Yeah just careless with the words there. But there is still some doubt in my mind as to whether or not there is the same potential for oil consumption when the engine is just spinning without spark or fuel injection. I understand that oil could still get past the rings regardless of whether or not the engine is firing, but it wouldn't be getting burnt off, so you may well get a thicker film build up and less consumption. I'm not 100% sure of that though, it's just a hunch.

 

Yes that's what I was referring to in my previous post John. Remember however that the context here is that of oil consumption, and as far as oil consumption goes it may not make any difference as to whether or not there is any combustion. Actually I think it's a somewhat open question of whether or not oil consumption would be effected in this state. I'd be interested in what other people opinions are on this.

 

I think the difference in the situations between ICE running and ICE spinning are, that with ICE running there are three strokes (4 stroke engine) of more pressure above piston than below creating pressure in the crank case.

This pressure can push oil up the bore of the cylinder that is on it's intake stroke.

When the engine is just being spun by MG1 there is no combustion stroke (the largest pressure difference) and no compression stroke (the next largest difference) to produce piston blow bye thus giving greatly reduced crankcase pressure and less oil being pushed up the cylinder on a greatly reduced intake stroke.

John (Bitprius)

 

In a high-speed glide the ICE is only spinning.

I don't live on level ground. In fact I don't know if we even have any. Also, remember that time and distance are two different things. My tank average speed is typically 34 to 37 mph, which means that for every highway mile it spends a lot of time going a lot more slowly and my car spends most of its distance in 45+ zones.

To me the issue with the 60% is not possibility but the relevance to the OP in a car that's done 100k miles. Any way you cut it, the engine duty for a Prius driven 16,000 miles per year is a lot lighter than a conventional car.

So, as Patrick says that consumption might be normal but I have thought it more easily fixed in a Prius with a less tired engine.

 

Now the argument is whether or not the ICE is actually "running" or not at highway velocity when fuel is cut off. That's a topic for another discussion altogether.

My main goal is to continue moving without slowing down. And I do my best to maintain a constant highway speed on the way to work at 0530 and on the drive home at 1445 with the cruise control set at 70 mph or lower. Light traffic volumes at these times. It's still difficult though because other drivers seem to have a problem with the 70 mph speed limit once they've passed me after tailgating me when they don't need to. Sigh.

 

My 01 is virtually never driven on the freeway. It is primarily a city use car. Every once in a while, it will see the freeway for 8-10 miles and on rare occasions, we will bring it to Nashville (70 miles).