V12 breathers revisited.

V12 breathers revisited.

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8Tech

Original Poster:

2,136 posts

197 months

Monday 27th June 2016
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After reading a number of posts on here referencing the oil contamination of the air filters and inlet manifolds on the V12 engine, and the various methods of explaining and fixing it, I decided to take a good hard look at the problem and trying to solve it once and forever.

I took note that whilst replacing all the hoses and valves concerned with the engine breathers seemed to rectify the fault, this was only a temporary measure, and whilst our cars generally do not do normal mileages, a full rebuild every 30,000 miles or so on the engine breather system indicated an inherant fault in the design.

If the aforementioned parts were an easy and cheap fix, then a more involved modification would be unnecessary, but with the requirement to remove the inlet manifolds to access the parts, and parts and labour going in at over £600.00, I decided to try a more lasting solution.

I firstly needed to understand how it all worked, and why the problem exists in the outset. Using this diagram as a reference, I will try and explain how the system works.



Hoses, part 7, are installed on the throttle bodies, downstream of the throttle plates, so at almost all times, these apply a vacuum to the top of two PCV (Positive Crankcase Ventilation) valves shown at position 2. This applied vacuum on the valves applies a regulated/balanced vacuum to the two oil separators via a “Y” connector and a pipe between positions “X” and “Y” to the rear oil separator, indicated at 11. This is connected directly to the front oil separator (10) by a pipe between them and causes a vacuum condition in the engine assembly.

So that there is not an excessive vacuum held in the crankcase, there are two pipes, “3” and “5” that allow fresh, metered volume of air to flow from the air intake, before the throttle body but after the airflow meters so that there is a constant fresh air flow through the engine case. This explains the name of the system as there is a positive flow of fresh air entering the crankcase, picking up any blowby gasses and oil vapours, and being reburnt through combustion by entering the inlet system.

Where the pipes allow fresh air to enter the engine through the camshaft covers, there is a one-way airflow valve at 4A and 6, known as “duck” valves so that air can enter the camcovers, but not blow out. The duck valves are known to fail, allowing oil vapour to flow back through the air “make-up” pipe and into the intakes, pre throttle.

The “duck” valves are so called because of their resemblance to a ducks bill where air flowing one way pushes the halves of the bill together but air from behind can flow easily.

HOWEVER, this system relies on engine intake vacuum to operate, which is greatest at small throttle openings. At high or full throttle, there is far less vacuum, and under these conditions, the increased blowby gases, build pressure in the crankcase, and this pressure is released through a further duck valve at position 4B where it travels in the opposite direction to the make-up air, and blows into the right hand side intake as well as through the two vacuum pipes.

If everything is working correctly, and the valves and separators are doing their job, there still seems to be an excess of oil vapour escaping into the intakes, usually at large and full throttle when the vacuum is low.

The ONLY place this oil laden vapour can flow is from the two separators into the “Y” connector through the pipe connection at “X-Y”.



I have decided to intercept this vapour at that point and install a proper oil separator/catch can by splicing into that pipe and running the oil laden vapours into an easily cleaned, condensating container, therefore keeping the high acid/fuel laden oil vapour away from the inlets, protecting both the air filters, the throttle plates and engine from ingesting it.

I decided to purchase a cheap oil catch tank to save time but upon opening it up, it was clear to me that it was pretty useless as it was so I went about modifying it as follows.

The empty chamber started out with just two connectors in the lid and a sight glass. There was nothing inside to encourage the oil vapour to condense and separate out and I could see that the vapour would simply go in one pipe and straight out of the other.

Firstly, I added a copper pipe, cross drilled into the inlet pipe aand to filter the air exiting the tank, I installed a small bronze compressor filter to the outlet fitting.



To force the vapours to the middle/lower end of the tank, I then added some stainless steel pan scourers into the bottom of the tank to separate the oil from the vapour.



To force the vapour down and through the scourers, I added a drilled baffle to isolate the outlet from the inlet.





With the scourer inserted in the bottom



followed by the baffle



The lid could be installed and sealed.

I replaced the flimsy oil hose in the “V” of the engine between the original separators



with some Aeroquip, high pressure oil cooler hose.



I found a space to install the tank nicely on the rear left of the engine bay, below the brake master cylinder.



and using the original bracket, (seriously over-engineered to hold a thin cable!) to hold the tank in position.





I used some Reflecta-Gold heat shielding I had spare to protect the side of the catch can. It fitted nicely down there.









I then ran one hose from the rear separator into the inlet of my catch can, and the outlet of the can into the “Y” connector at position Y.

Since making this modification, there has been no recurrance of the pools of oil in the small reservoirs situated just downstream of the throttle bodies, and no more necessity to clean the throttles every service.

12pack

1,533 posts

167 months

Tuesday 28th June 2016
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Very informative piece of work. This is a problem I didn't know I had. Is the oil pooling seen in all the V12 engines?

8Tech

Original Poster:

2,136 posts

197 months

Tuesday 28th June 2016
quotequote all
I believe so. I dont know about the very latest cars but it certainly seems to be the case for cars from 2004 to at least 2012.

I suppose that if your service schedule stipulates cleaning the throttle bodies at every service, then you still have the issue.

paulrog1

983 posts

140 months

Tuesday 28th June 2016
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Very good write up, very impressed with the oil catch tank.

For anyone who wants to know to see if your car has the oil breather problem just either remove the air intake pipes from the throttle bodies and if you see pooling of oil then you have a problem. also remove the airfilters, if there is oil soaked into the filters.

My car doesn't have this problem, which is good as it's got plenty of other problems..........



flyboy1

19 posts

99 months

Tuesday 28th June 2016
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Hi, I have had Oil in manifolds and think have found a simple fix. Soon after the last service I had a series of faults and errors. Some re-set after a restart and others required the use of OBD tool once fault was investigated. The main issue was erratic idle and a throttle over torque error. Stripping the throttle barrels off the manifold showed a pool of oil in both manifolds and oil round one of the butterflies. Web search indicated this was PCV valve issue, as I had suspected and I raised whilst it was under warrantee. Over the last 6 months I have removed the throttle barrels to clean the manifolds several times and eventually made up and fitted 4 swirl pots in the vents to allow me to identifying the feed causing problems which was as expected via the PCV valve tubes downstream of the butterfly. As these valves are hard to access and should act as flow restrictors under high manifold depression I have fitted a pair of PCV valves from a large V8 in series at the front next to the swirl pots, feeding down stream behind butterflies, which has reduced the amount of pull over of oil to a tiny amount. I have removed the other two swirl pots in the upstream large bore pipes as not required. The result is I am now NOT getting rapid build-up of oil in the inlet manifolds, down the air filter pipes or on the butterflies. I also now have brakes that work properly for the first time not requiring excessive pedal pressure and an idle that is stable, no misfires or (touch wood) error messages. I do not know why Astons do not fit the PCV valves at the front where they can be serviced without need to remove manifolds and delve behind engine as there is no resonance or flow issue that dictates they have to be at the back (and cooking).

I know the PCV circuit is now working as temporarily blocking them so breathing was only via the right cam cover large breather downstream of the throttles making all of the crank case vapours pass along this tube. This gave condensing and water in the U tube as expected but fitting the new PCV valves returns air flow as it should be via the PCV pipes at normal light throttle and only though the large right U tube on WOT with makeup air in on the large left U tube.

Hope this helps I will probably remove the other two swirl pots after a few thousand miles if new valve continue to work so fix is just a pair of new PCV valves at bout £15 the lot.

8Tech

Original Poster:

2,136 posts

197 months

Wednesday 29th June 2016
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Where on earth did you put 4 swirl pots? Do you have a picture?

The Ford PCV valves installed by AM (from an old Fiesta!) need to be mounted vertically, probably why they never fitted them horizontally at the front.

3200gt

2,727 posts

223 months

Wednesday 29th June 2016
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Old old problem on all v12 Aston engines. had it on my DB9 10 years ago. I fitted catch tanks and solved the issue much to the ridicule of this AM forum then. Caused by the PCV valves being mounted in the wrong orientation. I'm amazed AM haven't changed it yet.

DB9VolanteDriver

2,612 posts

175 months

Wednesday 29th June 2016
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So, who's right regarding PCV orientation? On the face of it, since there is a problem you might think vertical is wrong, but on the other hand that seems preferable to me to keep oil at bay. Maybe it is the 'hot' location that is the primary reason the valves fail rather than their orientation.

I do agree that at the very least they should be in an easy to service location, no matter the orientation needed to do so. At a few bucks apiece, I would have no problem changing them every 5 to 10k miles if needed, as long as I didn't need to pay a ridiculous labor charge either in money or my own time.

flyboy1

19 posts

99 months

Thursday 30th June 2016
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Valves I used are from Jeep and are all metal items. They seem to work in any orientation (vertical on Jeep) but found work perfectly slightly inclined.

Not sure if these photos will load never done this before.





Swirl pots were small units I custom machined up from solid aluminium with cyclone separation and baffles to fit in place of the lower larger U tubes and the ones shown in line with the PCV valves. Pots can be drained via port and tube in base, blocked off in use.

The pots are not needed as so far not had any more oil come over but will leave for now just in case as only done 1000 miles since fitting. Without them PCV valves just fit in line with plastic vent tubes and short tube sections cost for pair £15.

flyboy1

19 posts

99 months

Monday 4th July 2016
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8Tech, I notice your catch tank was fitted with inlets removed. Can you get to the connections by just removing the centre cover plate as I think it is much better to do one separator as you have than several small ones at source as I have had to do further down stream.

After enthusiastic cross country run to Burghley found a small amount of emulsion in the right lower large breather U tube so refitted swirl pot to intercept. After a good run today to dealer for service all I got was a little water in the bottom of the swirl pot but nothing in the others. Did you replace your PCV valves by the way?

8Tech

Original Poster:

2,136 posts

197 months

Tuesday 5th July 2016
quotequote all
No, the inlet manifolds need to be removed to get to the connection between the rearmost block oil serarator and the "Y" piece.

Once fitted however, this is not a problem because the new catch tank is easily accessible and can be removed and drained from the drain plug on the bottom.

Next time it is off though I intend installing a permanent fitting into the wheel arch from the catch tank so that it can be drained very easily without even touching the catch tank itself.

I will be changing my oil and filter this week so will see how the intakes look after a similar trip to Burleigh this last weekend.

Did you see my install on the car? I left the bonnet open for anyone to see.

flyboy1

19 posts

99 months

Tuesday 5th July 2016
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8tech,
No did not see your car there were so many to look at. You could put an auto-drain in the bottom, or in line with a drain tube. A simple one way valve will allow it to drain when stopped as when running always negative pressure. Alternative is simple tap.

Pity cannot get to the pipes without manifolds off, will have to wait until plugs need doing.
Did you replace the PCV valves as well?

8Tech

Original Poster:

2,136 posts

197 months

Tuesday 5th July 2016
quotequote all
Yes, whilst I was in there, I tested the duck valves which functioned perfectly so I replace the PCV valves as a matter of course.

cressell

35 posts

68 months

Monday 10th June 2019
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Hi!

Sorry for the necro, but I'd love to see the pictures added in the posts above. They seem to have been taken down since, any possibility to have them refreshed?

Graze01

1,034 posts

91 months

Monday 10th June 2019
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Fabulous resurrection of a tech thread

Thanks 8 Tech and Flyboy for the details

Graze

Squaremeal

180 posts

138 months

Monday 10th June 2019
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Yes, would be very interesting to see progress on a possible fix for this Achilles heel on the V12

8Tech

Original Poster:

2,136 posts

197 months

Monday 10th June 2019
quotequote all
cressell said:
Hi!

Sorry for the necro, but I'd love to see the pictures added in the posts above. They seem to have been taken down since, any possibility to have them refreshed?
They are still all there. I cannot see them on Google Chrome but they work fine with Firefox.

paulrog1

983 posts

140 months

Monday 10th June 2019
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Very interesting topic, as a DB9 owner I have been aware of this problem and i have even replaced the 2 PCV valves a few years ago together with the coils/plugs.

Its a pity the PCV valves are in such an inaccessible place as you need to remove the inlet manifolds etc, so I have an idea-

As you all know the PCV valves are in a couple of rubber hoses, we could replace them and use longer lengths of hoses to move the valves to a more accessible place so its easier to replace them?? Just purchase a long length of proper hose of the correct sizes and move the valves to an easier place to replace them?

I'm not sure if you lengthen the hoses it may affect the positive crankcase ventilation system, i hope an engineer here could answer that.





Phil57DBS

196 posts

74 months

Wednesday 12th June 2019
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A Big Interest because always oil in Intake manifolds...!

Closed system or Open system ?
https://www.jbspowercentre.com/wps/p...20IJGE61AK1...

Lawts0908

190 posts

86 months

Friday 14th June 2019
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Great thread and interesting read.
I’m surprised there are no independents marketing a fix for this problem, ie BR etc. Mike, any comments??