PCV Valve Replacement Questions

Some of the items @farmecologist references I have done as well (including the BGProducts EPR treatment). But this has also been in the last month or so and is too early to tell or report on. Will keep the thread referenced updated with my findings as well.

So 2 data points coming soon.

 

True in theory, but has there ever been a clear case of replacing the PCV valve actually curing excessive oil consumption in a 3rd-generation Prius? Usually, I gather, that's more a case of grasping at straws.

 

Or maybe asked in a different way:

How many PCV valves have been found to not be functioning or checking?

My bet on this is low and then you have to look elsewhere. I know in my case the PCV valve was still checking at 120 k when I first began to notice oil consumption. And replacing it did not solve the small drink of oil.

Continued diligence with oil level monitoring on the dipstick and adding as needed while troubleshooting the other causes of oil consumption will help keep the problem from getting worse.

 

I'll confess to not even having a full grasp of how the pcv valve works. Let me take a stab, just from what I've read in the last few days, without peeking:

The PCV (Positive Crankcase Ventelation) valve connects high up on the crankcase wall. A hose runs from it's other end to the intake manifold. When there's high vacuum in the intake manifold, it's sufficient to pull a spring-backed ball bearing off it's seat, and allow air to flow from the crankcase to the intake manifold.

This action creates a partial vacuum in the crankcase. To counter this, another hose runs from the valve cover, to the air intake snorkel, somewhere between the throttle body and the air filter.

In the old days, crankcases just vented to the atmosphere, but that was causing pollution, so the PCV valve was introduced, basically to run the crankcase air back into the combustion chamber. But now, if the PCV valve is stuck in the shut position, the crankcase can't vent, which it needs to do, what with all the piston motion.

From here on I'm completely out of my depth, but thinking: bad things start to happen, with a poorly vented or completely sealed crankcase, specifically oil getting up past the piston rings, or perhaps getting into the intake via that second hose??

This seems to cover it:

 

Definitely buried in there. Easiest to do when the intake manifold is off. I did mine off cycle but will do it again when the intake manifold is off at 200 k miles.

You end up getting more people for the end of March meet up?

 

I think I talked @mmmodem into coming. You mind if I ask someone else who might be interested?

I got it on the calendar, so I should be good.

 

I'll see what I can do.

 

It's easy to get that description sort of backwards-ish, because it's not exactly intuitive.

The condition where manifold vacuum is highest is idle (well, deceleration can be even higher), when the engine is sucking against a closed throttle plate. So you have a very high manifold vacuum, but the engine is not producing much blow-by gas (and anyway, allowing much extra airflow into the manifold would mess up the idle).

The condition with the most blow-by gas is full-power operation, which is also when the throttle is way open and the manifold vacuum is relatively low.

So the PCV valve is an odd critter that allows more flow when the vacuum pulling on it is lower. The pintle on the inside moves to restrict flow as the manifold vacuum increases. (It can also close if manifold pressure goes positive, to prevent backfire from reaching the crankcase.)

There's a "University of Toyota" class on its theory of operation; the course material is on techinfo.

-Chap

 

Yeah I recall now: high vacuum at idle, and it drops as you accelerate.

 

Has anyone tried a PCV catch can? I can get a compressor water separator at the hardware store for around $10

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The "catch can" settles out the oil in the blow-by and traps it so that it doesn't reach the throttle body and intake manifold. I've used one in the past and it works. All I did was buy the water separator, remove the foam filter, add hose nipple to inlet and outlet, cut the PCV hose and attach. This was on a '95 Saturn SL2 with lots of blow-by. I ended up emptying it every couple of weeks.

 

The weird labyrinthine wart on the engine block that the Gen 3 PCV valve is screwed into is an oil separator.

-Chap

 

For the Toyota spec'd PCV valve thread sealant "adhesive 1324, three bond 1324", it looks like Loctite 271 is equivalent. See attachment:

 

For a counterpoint, looked up a Honda instruction. Basically: take off old one, put in new one, no mention of tricky coatings. I think I like that.



There is a washer though.