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Old 12-07-2009, 11:10 AM   #1 (permalink)
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PCV valve questions

Here are my questions, please read on for more detail.
  1. What exactly does a PCV valve do?
  2. Between a clogged PCV valve and a dirty air filter, how much %FE could it cost?
  3. Should I be worried about the remaining "yellow gunk" I wasn't able to remove?
I recently got my tires rotated and had a "21 point inspection". Among the things that were recommended to be done were:
Replace burnt out tail light
Replace (suspected) clogged PCV valve
Replace air filter
They wanted $30 each ($90 total) to do the work, and it would take about an hour... I just replaced my tail light, PCV valve, and air filter on my own for about $15 or $20, and it took me about an hour. They had said that the PCV valve was probably costing me 10% fuel economy and the air filter another 10%. They said that the clogged PCV valve would cause oil to get on the air filter, reducing it's efficiency. The PCV valve was sure clogged, with a fairly thick, yellow gunk, along with a lot of the line that connected to it and clogged back into the air filter compartment. I did everything I could to clean out the gunk from the line (and it is good and clean now), but I just couldn't clean the channel back into the air filter compartment completely (two 90degree bends makes it really hard to clean). Should I be worried about this? Is there a trick to cleaning it out? I drove it today and didn't notice anything any worse than I had before, but it was clogged before... I just don't want to have to replace the PCV valve again and again as the gunk makes it's way out of that channel. Thanks guys.

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Old 12-07-2009, 11:58 AM   #2 (permalink)
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The PCV valve, (positive crankcase ventilation) pulls vapors out of the crankcase during engine operation so that they don't condense when the engine cools down, into potentially corrosive or solvent substances in your oil.

This results in a longer lasting engine, and longer lasting lubricity of the oil.

I've never heard of a PCV getting yellow gunk on it... maybe from using a paraffin based oil? ( PureBase is the trade name of a paraffin oil from Pennzoil for example)

Frankly I've never had a clogged PCV valve, ever, in any car I've owned. And they should be around 5 bucks, not 30 - or you can probably clean the valve itself with a little solvent. It's just a one way ball valve, nothing fancy.
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Old 12-07-2009, 12:17 PM   #3 (permalink)
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I guess that raises another question...

4. How am I to know whether or not the PCV valve is working?

The guys that told me it was "probably clogged" said so based on there being oil in the air filter compartment. Is there another way of telling without actually removing the filter and inspecting it?

I am using a fully synthetic oil, Mobile 1. I don't know whether or not it is paraffin based.

And yes, it was $5 ($30 was to have them fix it).

Thanks for the info
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Old 12-08-2009, 12:33 AM   #4 (permalink)
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Quote:
Originally Posted by wyatt View Post
I guess that raises another question...

4. How am I to know whether or not the PCV valve is working?

The guys that told me it was "probably clogged" said so based on there being oil in the air filter compartment. Is there another way of telling without actually removing the filter and inspecting it?
Wyatt ,
Easiest way is to remove the valve and shake it.
If it is working as it should it will rattle telling you all is OK.
This is usually a ten minute job and needs no special tools or talent.
Even I can do it!

Oil in the filter is not a major problem and is most likely oil vapours condensing on the cooler metal parts of the air filter.

Pete.
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Old 12-09-2009, 01:16 PM   #5 (permalink)
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Quote:
Originally Posted by wyatt View Post
The guys that told me it was "probably clogged" said so based on there being oil in the air filter compartment. Is there another way of telling without actually removing the filter and inspecting it?
Without being familiar with your specific model of car, I'd venture to say that if I was seeing a lot of oil in the air filter housing I'd look for overfilled crankcase oil sump, or excessive blowby from a badly worn engine, or excessive restriction in the air intake (causing a meaningful amount of vacuum on what should be the atmosphere side of the throttle body).
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Old 12-09-2009, 01:31 PM   #6 (permalink)
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Oil in the crankcase is filled between the two dots on the dipstick, same as always. The engine runs great (it leaks some oil, but I never have to add any), so I wouldn't say my engine (even with 170,000 miles) is excessively worn. I will check for possible restriction, something I hadn't even considered...

I think I will be checking the PCV valve every week or so to make sure it's not getting clogged up again. Thanks guys, I will keep you posted if anything odd happens.
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Old 12-14-2009, 01:03 AM   #7 (permalink)
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it could be as simple as dramatic oil change. some sythetics conquer some regulars, and the battles commence.
I just added sytnthetic this past year to a 23 year old engine, the filter gets strange stuff. The curve of this is less and less, and knew the sythetic is the cleaner and tougher, kicking out the most stubborn of years. Some actually do not survive the change.
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Old 12-14-2009, 08:43 AM   #8 (permalink)
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PCV has been required in the US since 1963. Before that the blow by from combustion was vented into the atmosphere through a tube. You could see the cloud of noxious fumes blowing out from under the vehicle.

By creating a slight vacuum in the crankcase PCV actually reduces oil consumption somewhat. A plugged PCV allows crankcase pressures to become elevated, which would actually make oil consumption worse. We used to buy cars with plugged PCV valves, in the 1960S. when I was a teen. A 63 Valient would burn a quart of oil in 400 miles, with 40k on the odometer. After cleaning the PCV consumption would drop to 1 quart in 1500-200 miles. These were engines that were caked with sludge internally and had not been well maintained.

The slight vacuum in the crankcase with a properly functioning PCV would help very slightly with pumping losses inside the crankcase.

If your PCV is plugged, your oil consumption would be significant.

The substance you are seeing in your PCV system, does not sound normal (just my opinion). It may be the beginning of a head gasket problem or something else that is allowing condensation or coolant into the bottom end of your engine.

It could also be due to very short trips without sufficient warm up time, for the condensation to be heated enough to vaporize and flow out through the PCV system.

Carefully monitor your coolant level for slight losses. Try to drive at least 50 miles occasionally, especially in very cold weather, or at least combine trips to the point where the oil in your filter gets too hot to hold your hand on the filter.

If necessary restrict flow to the radiator to enhance warm up. Make sure you have a properly functioning thermostat. Hold your had on the top hose and you can feel the dramatic change in temp when the thermostat opens. If not it is probably not working properly.

regards
Mech
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Old 12-14-2009, 11:42 AM   #9 (permalink)
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The car is burning some oil (I can smell it when stopped), but not enough to register on the dipstick. It is also leaking some oil from the head gasket and around the oilpan, but once again, does not register on the dipstick. It may not be a bad thing for me to replace the head gasket and see if that helps, if nothing else, it will stop the leak on the top of the engine (which may be the burning oil smell). I found out last night that the alternator needs replaced when the headlights were so dim I couldn't see much, so new belts, new alternator, and new head gasket... While I am at it, I should look into advancing the timing since people claim that helps (MPG wise).
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Old 03-18-2010, 02:23 AM   #10 (permalink)
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I had a similar experience before. I noticed yellow gunks on the PCV valve and took it to the car shop. The mechanic said that short drives could be a cause of it and so it accumulated.


Last edited by mikeross; 04-13-2010 at 04:13 AM..
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