How critical is the PCV system?

[Chris B.]

I'm trying to find out how important the PCV system is for an engine? I've been told mine might be clogged since under my fill cap has lots of sludge/crud build up(bought car used) but the car(Volvo XC70) runs extreemly well and burns no oil. Also UOA's show very low wear. I did the glove test and put a latex glove over the oil fill hole and it sucked it in. I was told that means the PCV system is working.
If my PCV system is indeed not working properly and I drove it that way for a long time would the engine still have a long life? What kind of problems might I see? Many thanks!

 

[Quest]

Very! A clogged PCV valve will not only causes sludge, but the inability to vent those obnoxious gases such as moisture, condensation, blowby, etc. will accelerate the deterioration of your otherwise still lots of life left motor oil.

and if you choose to ignore it, your engine will start burning oil fairly soon due to oil control ring sticking(jammed) due to decomposed motor oil. Also: most seals, such as cam/crank esp. valve stem seals, the elastomers do not take deteriorated motor oil very well and will become brittle/hardened as the elastomer materials being attacked by these polluted motor oils. As a consequence: your engine will start to burn oil far sooner than expected.

 

[OLAFF]

If you ever think its failed, the easiest thing to do is pull the dip stick out a 1/4" and let it sit that way, anything blowing down in the bottom end will escape.

 

[Cup of Joe]

Originally Posted By: Catera
If you ever think its failed, the easiest thing to do is pull the dip stick out a 1/4" and let it sit that way, anything blowing down in the bottom end will escape.



Road pipe.

No PCV valve and a piece of 5/16 fuel line run to the bottom of the car.

 

[ARCOgraphite]

Originally Posted By: Chris B.
I'm trying to find out how important the PCV system is for an engine? I've been told mine might be clogged since under my fill cap has lots of sludge/crud build up(bought car used) but the car(Volvo XC70) runs extreemly well and burns no oil. Also UOA's show very low wear. I did the glove test and put a latex glove over the oil fill hole and it sucked it in. I was told that means the PCV system is working.
If my PCV system is indeed not working properly and I drove it that way for a long time would the engine still have a long life? What kind of problems might I see? Many thanks!
That glove trick does NOT mean the PCV is working - that is just normal crankcase pressure variation due to piston position. Fix the PCV, its not expensive. Also take off the VC and clean them and put on new gaskets. Fix it NOW! All that sludge you talk about makes me worry about a once blown or going head gasket. Any Pics?

 

[alphasparky353]

If its there it's important.

 

[defektes]

clogged PCV can also cause blown out gaskets

 

[mechtech2]

Pulling the dipstick may do absolutely nothing, as it may be immersed in oil at the lower end.

PCV systems are important. They provide a flow through of air to purge blowby gasses out of the crankcase and valve cover. This stuff is crud, and has filth and acids, etc..

You have an in, and an out. Both have to be operating right. Negative pressure for flow is provided by intake manifold vacuum, in gas engines. Full throttle or excess pressure can vent out either through the PCV valve or the inlet. The vapors and liquids are normally 'recycled' through the engine again.

I use a catch can to trap these contaminants, as I don't want that stuff on my valves or combustion chamber.

 

[calvinnnnnnnnn]

take out your pcv valve, shake it, if you hear ticking its working fine.

you really dont need to purchase a new one, spray some carb cleaner through it and its almost as good as new

 

[benjamming]

A PCV valve can pass the "shake test" & still be bad.

 

[ARCOgraphite]

The hoses and in-and-out ports have to be free and clear too!

 

[gavinl]

Let's clarify something here, the Volvo in question has a 5cyl does not have a usual PCV system consisting of a rattle valve. It is a complex maze of a vapor catchcan with an assortment of hoses. The can and hoses do clog up over time.

Here is a parts diagram of the 5-cyl Volvo PCV system:

As previously mentioned, having a clogged PCV system will cause oil leaks out of the filler cap (associated with a worn cap gasket), rear main seal leaks ($$$), leaks out of cam gear seals, etc.

In short, replace the PCV system! It's a high mileage maintenance item.

 

[heypete]

The PCV valve on my friend's Toyota Tercel cost about $2 at AutoZone. Why not replace it?

While the Volvo PCV system is likely a bit more complex, it's certainly less expensive than replacing a damaged engine.

 

[Chris B.]

Thanks guys!
Well the car has 60,000 miles and burns no oil. It only had a nasty oil fill hole and cap. Another Volvo guy told me the PCV was causing this build up around the fill hole. I cleaned it by hand 6,000 miles ago and it's still spotless and no oil burning. It's a $350-400 job so I don't want to replace it if it is not needed. So it's showing no signs of a clogged PCV system. How do I tell if it is needed?

Here is a link to my problem that is now over a year old and the cars seems 100% healthy. That is why I'm doubting the PCV is bad:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1314044#Post1314044

 

[JTK]

Chris, like you say, your data is showing everything is fine. I've seen perfectly functioning engines/PCV systems sill leave some mayo on the underside of the oil filler cap. It depends on your operating conditions and the nature of this particular engine.

Joel

 

[mechtech2]

benjamming - Thank you. Everyone shakes a PCV valve. But it shows nothing about seat or pintle wear, plugged orfices, bad springs, etc..