I observed something lately on my car and went on a search as to what the problem could be. these were what i noticed.
1. Poor Mpg in city driving. really poor though i understand i stay in a very crowded town but that really doesnt explain the really low Mpg
2. Synthetic oil turning black after less than 3000 miles of use. Most of these miles were highway miles so sludging shouldnt be an issue. (I have done a cat delete sometime ago so that rules out blocked catalyst)
3. Visible crud deposit on oil filler cap. This was a give away sign that sludge was gradually building up in my engine.
4. Oil consumption. My car needed another 1 litre of oil at 3000 miles when i checked the dip stick. I was alarmed. That's a very high oil consumption bearing in mind i had wanted to carry out oil change at 5,000 miles since i was using synthetic and had travelled mostly on the highways
5. oil stains around the dipstick hole. I noticed what looked like oil stains around the base of the dipstick slot near the base of the engine.

So i searched the internet and found out that something called a PCV valve could cause all this symptoms. Its job is to vent the crankcase and prevent excessive pressure buildup. It also takes away unburnt hydrocarbon that escaped into the crankcase through blowby. Somehow people think its not a part that should be serviced like the IAC, TB, and other stuffs that need attntion after say 50,000 miles or so.
I proceeded to check mine out. To my dismay, mine was blocked by very thick hardened oil deposit. the previous owner most likely never serviced it and it got really fouled up and got blocked.
So i was practically driving around with an engine that had no means of venting its excess pressure.
I cleaned it up as best as i could and have put it back. I blew in air to check if it works and it still worked. Its supposed to let air pass through from one side but not from the other side like a check valve. The PCV is located on the valve cover of my car (Toyota camry 2.4L 2AZFE) and is connected to the intake manifold. You can google where yours is located. I really hope people carry out this simple fix to save themselves a lot of headaches especially if their cars are high mileage like mine (above 100,000). I wish i had pictures but did the work at night so couldnt take pictures. Will see if i can download pictures from the internet. cheers.
Its something you can do yourself if you have got ten minutes or more and u don't have to take off the valve cover. All i used was a nose plier, 10 and 22 spanner, carb cleaner and iron brush.

9ice, my engine is same as urs. Pls I need pics nd directions on hw I can do dis. Wat was d effect on d car after d clean up?

9icetoo: I observed something lately on my car and went on a search as to what the problem could be. these were what i noticed.
1. Poor Mpg in city driving. really poor though i understand i stay in a very crowded town but that really doesnt explain the really low Mpg
2. Synthetic oil turning black after less than 3000 miles of use. Most of these miles were highway miles so sludging shouldnt be an issue. (I have done a cat delete sometime ago so that rules out blocked catalyst)
3. Visible crud deposit on oil filler cap. This was a give away sign that sludge was gradually building up in my engine.
4. Oil consumption. My car needed another 1 litre of oil at 3000 miles when i checked the dip stick. I was alarmed. That's a very high oil consumption bearing in mind i had wanted to carry out oil change at 5,000 miles since i was using synthetic and had travelled mostly on the highways
5. oil stains around the dipstick hole. I noticed what looked like oil stains around the base of the dipstick slot near the base of the engine.

So i searched the internet and found out that something called a PCV valve could cause all this symptoms. Its job is to vent the crankcase and prevent excessive pressure buildup. It also takes away unburnt hydrocarbon that escaped into the crankcase through blowby. Somehow people think its not a part that should be serviced like the IAC, TB, and other stuffs that need attntion after say 50,000 miles or so.
I proceeded to check mine out. To my dismay, mine was blocked by very thick hardened oil deposit. the previous owner most likely never serviced it and it got really fouled up and got blocked.
So i was practically driving around with an engine that had no means of venting its excess pressure.
I cleaned it up as best as i could and have put it back. I blew in air to check if it works and it still worked. Its supposed to let air pass through from one side but not from the other side like a check valve. The PCV is located on the valve cover of my car (Toyota camry 2.4L 2AZFE) and is connected to the intake manifold. You can google where yours is located. I really hope people carry out this simple fix to save themselves a lot of headaches especially if their cars are high mileage like mine (above 100,000). I wish i had pictures but did the work at night so couldnt take pictures. Will see if i can download pictures from the internet. cheers.
Its something you can do yourself if you have got ten minutes or more and u don't have to take off the valve cover. All i used was a nose plier, 10 and 22 spanner, carb cleaner and iron brush.

This post is so on point. The PCV can be the root of many oil burnout leading to excessive oil usage. Somethings the PCV might have been damaged- as is often the case with many mazda cars - and would need to be changed. The sad part is most road side mechanics doesn't even know what a PCV is or what it looks like. Doing due investigation on ur car problems goes a long way. Thanks for the post.

chukel, my car had all the symptoms above which led to my search. Although rough idle and backfire is another symptom, i didnt experience those. here is a step by step way of doing it.
You will need a 10 and 22 spanner and a plier. A combination (ring and flat), will be ideal.
You will equally need a solvent like thinner or alchohol or fuel. (thinner worked better for me)
Remove the plastic cover on your valve cover with the ten spanner.
you will see two tubes protruding out of your valve cover. the tube on your right is routed to the air intake (just after your air filter) while the tube at the back of the valve cover to your left is routed to your intake manifold. that tube on the left at the back of the valve cover is connected to the pcv valve.
With ur plier remove the clip attached to it and slide the clip back.
then pull the tube out of the pcv valve. Sometimes the tube refuses to pull out (it happened to me). just twist gently and pull. If it can twist but wont pull out, let it be.
then with the 22 spanner, loosen the pcv valve the tube was attached to the valve cover.
with the pcv out of the valve cover, it will be easier now pull it out of the tube if it is still connected by using a plier and then applying a twisting and pulling motion. be careful with the tube though so u don't crack it. After so many years, they become a bit brittle.
when u have got the pcv out, inspect the end that was inside the valve cover for deposits and clean out as much crud as you can with the solvent and brush. (in my case, i soaked the pcv in thinner for thirty minutes)
perform a check on the pcv valve by shaking it. If it rattles, it means the spring is still okay.
blow in air with ur mouth from the end attached to the valve cover. if air comes out, it works. then blow in air from the barbed end connected to the tube. Air shouldn't come out from the other end. if air does come out, then it means it is time to replace ur pcv valve. it is very cheap i hear. about 3k or less.
i hope this helps. Please when reconnecting the pcv valve, do not tighten it too much cos the valve cover is just magneium and isnt very tough.
Also wait for the thinner to dry out very well or rinse off with petrol befor u fix the pcv valve back. thinner is a nasty solvent and u dont want it in your engine.

pcv valve location

the valve itself

U r wonderful. God bless um I wil check mine oUt. In place of thinner, can I use carb cleaner?

Simple test to know if the valve is still good after cleaning- shake it and u should hear/feel something moving inside.
If not, you should replace it.

Your oil turning black after synthetic means your engine already has a lot of sludge the new I'll is doing its job