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Positive Crankcase Ventilation Clean Up.

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Old Apr 5th, 2011, 18:32   #1
Paul240480's Avatar

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Default Positive Crankcase Ventilation Clean Up.

Positive Crankcase Ventilation

It is common for this system to clog up if neglected. The result will be oil leaking through the rocker cover gasket, or worse. The first time mine blocked up, the oil dripped onto the exhaust manifold. If yours has got to this point, budget for a new rocker gasket too.

There is a flame trap inside one of the pipes, Volvo decided this was no longer needed & as part of their service schedule, I understand they removed the flame-traps during. Mine was not 'dealer serviced', so I found mine still in place when I first did this job in 05.

So, first we need to identify the bits in question.

This is one of the pipes; this is attached to the air intake manifold with a brass connector. The pipe pushes onto the connector & the connector is threaded into the manifold. A 15mm spanner is required to undo it.

If you follow this thin pipe down it will take you to the flame trap holder Pic taken off the car so you know what you are looking for.


It is quite dark down there & there are lots of other pipes so take your time & familiarise yourself with the location.

There is a 'fatter' pipe coming from the flame trap & holder which connects below the big rubber 'bellows.


The aim here is to remove these three parts, the 'fat & thin pipe' & the flame trap holder, for either cleaning or replacement. We shall also clean up the 'venturii plate', bear with me....

The pipes are all push fit, but do bear in mind that the plastic holder will be brittle, especially that thin 'nipple' for the thin pipe. Believe me when I say it is easily snapped off!

So now we are ready to start. You can undo, with your 15mm spanner the brass connector & separate it from the thin pipe. If it is at all blocked up, spray some carburettor cleaner into it to clear any gunk, if needed a straightened paper-clip can be poked through it to clear stubborn gunk.
The connector:

Looking into one end, after being cleaned:

Now look into the 'hole' in the air intake manifold, where the connector threads in:

If needed shine a torch into it & make sure it is clean & gunk free. If not, use something like a straightened paper-clip to hook any dirt out.

Next, directly below the air intake manifold is a big rubber bellows. We shall remove this. First note it's position, & mark with tippex on the bellows and where if sits on the body, so that it goes back in the same place:

There is an arrow on the bellows, if you can find that, you can note it's position, & use that as your marker.
Undo the two jubilee clips on the bellows & gently ease the bellows out:
Here I have removed mine & put tippex on the arrow, so you know what to look for on yours:

You should be able to see the flame trap holder more clearly now, with the belows out of the way:

(The 'plate' here in the 'bowl is the venturii. Yours may be clean like mine is now. It may have a layer of thick oily sludge on it, if the system is blocked up. Mine certainly had in 05. Clean it out using paper towel & carb' cleaner. Be gentle with the plate it needs to remain in it current position).

Now, you should be able to reach into grab the flame trap holder & disconnect the fat pipe from it. Then you can pull the holder itself off, & finally carefully remove the thin pipe from it.
So now you will have these two bits & the thin pipe:

I'm afraid I didn't photo the fat pipe (brain gone), but you can now pull gently free from here:

If you cannot get a good grip on it, you may want to remove the vertical metal support for the air intake manifold, 4 bolts, two top, two bottom IIRC. The manifold will be fine.

Now it is time to clean the pipes out, if re-using. Carb' cleaner, again & maybe suitable items to poke any solid matter out. In 05 my 'fat pipe' was blocked almost solid!

Moving onto to the plastic flame trap holder, you will see it it actually two pieces push-fitted together.
You need to separate them. A screwdriver may assist as a lever if well stuck.

If yours still has it's flame trap in position it will be in here:

Look in the end & you will see one of these, that is the flame trap, it is a little sieve.

I popped a new one into mine as demo'. If yours is there, it will more than likely be black & blocked.
To remove it, get a small 'self-tapper' screw & turn it in by hand to one of the holes in the flame trap.

Then you can grip the screw with a pair of pliers & wiggle the trap out.

As mentioned the trap can be ditched. The holder itself, will no doubt benefit from a good clean up.

Now it is already to go back together, as is always 'famously' said, refitting is a reversal of the procedure!

If you are fitting a new thin pipe, it is a good idea to have a long length, so you can feed it down through the manifold & easilyy attach it to the two re-connected parts of the flame-trap holder:

If re-fitting the old cleaned out pipe, it is just a bit more fiddly. You may find yourself working by 'feel'. Note my shiney cleaned out Venturii plate

You can now re-fit the brass connector into the manifold & (if new cut the new pipe to size) & push on to the nipple on the connector. Then fit the fat pipe to the flame trap holder & then firmly push it home into it's 'hole'.

Quite a tight fit, this one do make sure it is 'well in'.

If you removed the vertical support for the air intake manifold, you can now replace it.

Then, check that Venturii plate for any crud that has fallen during the work & clean it out again if needed, then re-fit the big rubber 'bellows. Remember to align it to your mark. It is a bit fiddly to get the upper & lower 'collars' to fit right, so take your time & make sure they are neatly in place all the way round. Then tighten up the jubilee clips. We want a good seal here, no air leaking.

Fire up & go for a spin. If your system was blocked you should notice a much free-er revving engine. Should be a tad smoother too.

Finally, make checking this a once yearly 'job'.

I think that covers this one. If I've missed anything, or if you have any 'cunning tips', or if anything needs adding / correcting please feel free to post it.

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Old Apr 5th, 2011, 20:39   #2
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I'm glad you have managed to write this one up Paul. It is quite a fiddly one to do and diffficult to illustrate. It is possible to do with removing the bellows but as the venturi will always benefit from a gentle clean it is worth doing at the same time.

If the manifold support bracket is removed do make sure it is refitted tightly. I have had several instances over the years of the bolts coming out and then the manifold coming loose causing all sorts of running problems due to air leaks.


Original thread here.
A Volvo is for life not just for Christmas!

Last edited by cumbrianmale; Apr 5th, 2011 at 21:41.
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