Oil consumption at 171,000 miles

Soooo, it's valve guide seals after all!!! Nice!!!

Why don't you just replace the seals?

 

Why? What benefit do you perceive from that?

The use of B results in less regenerative braking (therefore, worse mpg) as compared to leaving the gear selector in D and just pressing on the brake pedal.

If your traction battery shows 8 green bars and you are still heading downhill, I could see shifting into B given that circumstance. The traction battery doesn't need more charge, the braking system will rely upon the friction brakes instead of regen, and by spinning up the gasoline engine, that gives the friction brakes less opportunity to heat up as you continue your descent down a steep hill.

 

First up let me say yes, many other owners have noticed some amount of oil usage, particularly after 100k miles. (What mileage are you currently at btw?).

Now let's look at things you're doing wrong.

1. Using "B" mode doesn't necessarily change the amount of friction brake usage. The Prius uses regenerative braking as much as possible, so in normal driving simply leaving it in "D" and braking as usual will mostly avoid friction braking anyway (as long as you don't brake too hard). Some of us use "B" mode in mountains on longs descents as it delays maxing out the HV battery charge, and does slightly reduce the need for friction braking (under these circumstances).

2. The use of "B" mode probably has little to do with your oil consumption issue. It's true that using "B" mode does make the engine spin more often, so theoretically might slightly increase oil consumption, but the underlying oil consumption problem is a completely separate issue.

Much more likely (than "B" mode) to contribute to engine wear and increasing oil consumption is your reluctance to top off your oil *before* it gets low. Oil consumption of around one quart (or a bit more) over an oil change interval is not in itself a serious problem, letting it get too low however is. Remember that the Prius only has about 3.7 quarts of oil, which isn't a lot. So check the dipstick regularly and top off before it's even close getting to low.

 

That bit of information is pretty much meaningless without knowing the MILEAGE since the last change.
I'm glad that the high mileage oil worked for you but you still need to keep a close eye on it.
Some find that a good fairly long term Band-Aid but others find that the consumption creeps back up fairly soon.

Because that's a fairly expensive engine repair that doesn't make economic sense in most situations.

 

You can get a used engine out of a donor car for about $500, and I can't imagine that it would be substantially more expensive to replace rather than repair.
The OPs vehicle already has 170,000 miles on the clock.
I'm betting that a little extra attention to the dipstick and frequent topping off will probably solve the problem until enough other things break to illuminate the "change owner" light.

Besides....it's probably not the valve guide seals.

 

I still believe that oil burning Prii have valve seal problems. I've never seen worn out cylinders on any opened Prius engine.

 

Old school thinking here... For oil to go out of an engine, it would either have to drip out from a gasket or seal leak onto the ground, or burn out through the tail pipe. If no ground oil spots are seen, then, it must be going out the tail pipe. For oil to go from crankcase, to tail pipe, not too many path's exist. Either bad piston rings, (worn out cyl. wall tolerances), bad valves seals, or possibly PCV valve (if a Pri still has one of those). There might be other paths for oil to get out of an engine, but those would be my most suspect.

I am confused on how using the engine as a compression break, (in "B") could cause more consumption. I mean,, think of all the manual transmission cars where that is the first way you slow them down, is by down-shifting. For that matter, even automatics, shifting into L1 or L2 on a down grade is usual. Even diesel trucks, compression brake all the time. Why would that create more oil consumption from the above mentioned oil exit paths?

I do agree, using the brakes on the Prius is better than B for regeneration n all, but to not use "B" for what it was meant for, (long downgrades), out of fear of engine wear, or oil consumption, does not make sense to me.

 

A diesel using a compression brake is a totally different thing. The exhaust outlet from the engine is blocked so causing lots of back pressure in the cylinders.
In the Prius system the engine is used as an air pump pushing air "no fuel is injected and the throttle plate is closed" through the engine and out of the exhaust. This results in a high intake vacuum that helps with the braking effect, but can draw oil down the intake valve guides pass through the cylinders and out the exhaust. In effect the is the opposite to the diesel scenario.

John (Britprius)

 

Sorry, had no clue about diesel blocking the exhaust outlet, but not having any gas flow during down hill breaking in a car is no different than a standard trans. car, or an automatic car downshifted into a lower gear. If it is pulling oil through the valve seals, well then, seals are the reason for the oil consumption. For sure for this thread, on a high mileage Prius, stop using "B" so much unless your really on a long down grade, or, like others said, replace your valve seals, potentially even do a "valve job". I am so 70-80's, I remember that was the "typical" fix for an older engine, do a valve job, to get it to last a fey more years. Now days, its pretty unheard of. Back then, the valve seats, would also need resurfacing by the time the seals were a leaking. The loss of leaded gas, the addition of "hardened valve seats" has pretty much eliminated "valve jobs". Now you just drive it, till its wrecked.

 

With to days engines valve jobs become much more labor intensive against those of the seventies.
Now most engines have twin overhead cams with inclined valves and at least four valves per cylinder. The valve clearances are done by selecting either shims or cam follower thickness involving assembling the head "after valve work has been done" checking clearances. Then dissembling fitting new shims or followers then reassembling and checking again. This is made even more complicated by having inclined valves. Meaning it is difficult to check clearances because of the requirement of turning two cams at the same time to keep valve timing correct to prevent inlet and exhaust valves clashing, and bending, or working with just one cam fitted at a time.

John (Britprius)

 

The high intake vacuum also tends to draw oil UP past the rings on the intake stroke.

Usually it is a combination of things:
Worn rings
Worn valve guide seals
Weeping gaskets and main bearing seals.

Anyone who has such dramatic improvements like reported by the OP here might have had a stuck ring or two that the different formulation of oil freed up and sealed again. The results might just be temporary too.

 

Very old boy here, but back in the day with engines directly connected thru to the wheels, we would judge the amount of blue smoke coming out the exhaust under hard acceleration and under hard engine braking with throttle closed:
If smoke under acceleration , then bad valve seals as hard acceleration stresses the valve train and valve guides, and oil would flow past the seals and out the exhaust.
If smoke under hard engine braking, then bad compression/worn rings as engine braking maximized the ratio of crankcase pressure to combustion chamber pressure, which would tend to push oil up past the rings and out the exhaust.
Checking compression directly to check on rings was also a common technique, as was removing the valve covers to check on the appearance of the valve stem seals. Not sure what is possible on the a Prius engine, but these are ideas.

 

how was branson?

 

IF.....that product looks like it is THINNER than your oil, you might want to STOP doing that, as it might be counter-productive in a high mileage situation.