Uh oh..exhaust in valve cover

1. If the dipstick is dry then the engine oil is low at least two quarts. The full capacity is 4.4 quarts so that is a serious problem.
2. If the engine lacks lubrication it is going to overheat and will not operate as effectively as it otherwise might, so reduced fuel economy will be one result (not to mention a shorter engine lifespan.)
3. If there is a lot of air pressure built up in the engine, evidenced by the flow of air coming out of the engine oil filler opening, that implies the PCV valve may be stuck (if you are lucky) or the engine has worn (if you are not lucky) to the extent that cylinder blow-by (due to worn piston rings) is causing the excess pressure.

 

I wouldn’t worry too much about the air blow by.

I’ve pulled the oil cap on the following and have always gotten the same feeling (never measured the flow rate of the air, but based on feel and sound is was about the same):

• 2010 Prius II at 175 k miles
• 2010 Prius III at 72 k miles
• 2007 Prius at 170-ish k miles
• 2018 Prius c at 300 miles

It probably has something to do with the Atkinson engine. But if you’ve never taken the oil cap off and listened, you’d think you’re up a brown colored creek without a paddle.

I’d worry more about the low engine oil and begin checking it frequently.

Good luck and keep us posted .

 

Mostly because it probably really is NOT blow-by......as the rest of your post indicated.

 

I've never noticed air blowing out when removing the oil filler cap.

I doubt your oil level measurement would be off by much, if you've got the whole car on jack stands, even if there is a slight slope.Yeah check again on level ground, but probably will still be very low.

 

how many miles on her? have you done the egr/intake service yet?

 

+1

Once you get all 4 paws back on the ground and rolling normally, start monitoring your oil consumption immediately.
You don't have to do hourly measurements or anything crazy like that.....just make sure your oil is topped off and then start checking every time you fill up.
Start reading up in this forum about checking and cleaning the EGR, Throttle Body, and Mass Air Flow Sensor in addition to things mentioned above.

You're driving an 11, and your info says that you're not taking a lot of cross country trips, so it's unlikely that you need plugs and yanking them is a PITA from what I've read....so we'll shelve the 'check the plugs' thing for later....but you may want to read up on that as well just in case you're burning more than a quart every 5k or so.

Good Luck!

 

Have you pulled the oil filler cap off while running?

 

Well maybe that's because you realize that you are NOT supposed to open it with the engine running......maybe ??

I hope that the OP knows not to check the oil level with it running either.

 

My 2015 has 15K miles on the odometer. I started the engine and opened the oil cap. There was a good flow of air but it did not smell like exhaust.

BTW, the air/fuel ratio is upset when you allow unmetered air into the engine. The engine will run lean.

 

No exhaust smell on any of the ones I listed above either.

 

Yeah maybe OP was doing these checks with engine running, @boa279?

Off-topic: I managed to forget to put the oil fill cap back on once, with an Accord. We ran it thus for at least a week, smelling engine smell inside the car. Probably not good for it...

I always figure now: if you're going to leave the cap off (useless no need): put in on the hood latch mechanism, in the way.

 

Unless your engine is REALLY worn out, the air coming out the oil fill hole is crankcase fumes....IE very hot oil.
And letting air into the crankcase of an engine in no way affects the air/fuel ratio.

 

Yes, I agree - and this is not the same as exhaust fumes.

We are talking about the Prius engine, which has a mass air flow sensor upstream from the throttle body. Any air that enters the engine downstream from the MAF sensor will not be accounted for by that sensor, hence the air/fuel ratio will become leaner and the engine idle quality will change. After the engine has warmed up and the engine ECU is operating in closed loop mode, the air/fuel ratio sensor will note that the combustion gases are lean and DTC P0171 will be logged.

If the engine has an air leak, such as an open oil fill hole, that will allow air to enter the PCV system, which is connected to the throttle body downstream from the MAF sensor. A similar situation would occur with a loose PCV hose or a loose or missing oil dipstick. A failed throttle body gasket is another example of a problem which allows unmetered air to enter the intake manifold.

This is why the trouble listing for P0171 tells you to check the intake system, the PCV hose connections, etc. The idea is to look for air leaks.

 

You guys got me thinking about this, I never heard it mentioned but it would be easy to try on any running car with a MAF.

 

Oops. Forgot about the PCV loop.

BUT.....the crankcase is "vented" by virtue of the intake vacuum and there is some air flow there. Where does the intake air come from into the crankcase to maintain this small flow ??

I thought there was a limiting factor in that "plumbing" that had little to nothing to do with how much outside air is allowed into the crankcase.

 

I haven't needed to work on my 2015 very much. I will tell you how this works on Classic and 2G Prius with the 1.5L engine; the 3G Prius 1.8L concept should be similar.

On Classic/2G, the PCV system has two connections to the throttle body. One connection is above the throttle plate (hence upstream from the plate) and the other connection is below the throttle plate. When the throttle plate is closed or mostly closed, vacuum is created in the lower connection compared to the upper connection, which encourages a flow of gases. Hence, air flows from the upper connection into the valve cover and ultimately the crankcase. The return from the crankcase and valve cover goes into the lower connection that has vacuum, then that dirty air enters the intake manifold to be burnt by the engine.

Since the upper connection is downstream from the MAF sensor, that sensor accounts for that air which is circulating around the engine crankcase. Also note that the air has been filtered by the engine air filter which is upstream from the MAF sensor and that all air should be entering the engine only via the engine air filter and MAF sensor.

 

Oy, my brain is full.