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Air Oil Separator Replacement
 
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Pelican Technical Article:

Air Oil Separator Replacement

Steve Vernon

Time:

8 hours8 hrs

Tab:

$6 to $200

Talent:

****

Tools:

Flathead screwdriver, 13mm socket

Applicable Models:

Porsche 944 Turbo (1986-89)

Parts Required:

Air oil separator, O-rings

Hot Tip:

Be prepared to replace the hoses

Performance Gain:

No more oil spillage

Complementary Modification:

Clean the engine block

The air oil separator on the Porsche 951 has two areas of weakness; one is the elbow hose on the top is prone to drying out and splitting. This will lead to problems with the function of the separator and can also lead to oil seeping out and causing a mess. The other area of concern is the two O-ring gaskets that seal the separator to the block. These are prone to drying out and failing leading to what can be major oil leaks.

While the replacement of the separator itself is relatively straight forward and simple, getting to it is another story all together. While people have claimed to have removed the AOS without removing the turbo you will need to cut the heat shield to get the bottom mounting bolt out and that is just not the right way to do it. Unfortunately, this means removing the turbo which means removing the intake manifold, etc. Please see our article on removing your turbo first for additional information.

The air oil separator (AOS) is located on the left rear of the engine under, well just about everything (red arrow).
Figure 1

The air oil separator (AOS) is located on the left rear of the engine under, well just about everything (red arrow). You will need to remove the turbo to get the AOS off, so please see our article on turbo removal for additional assistance.

With the intake manifold off you can see the main line going to the elbow hose on the AOS (red arrow).
Figure 2

With the intake manifold off you can see the main line going to the elbow hose on the AOS (red arrow).

This hose (red arrow) is attached to two of the vacuum lines (yellow arrows) that are attached to the cycling valve.
Figure 3

This hose (red arrow) is attached to two of the vacuum lines (yellow arrows) that are attached to the cycling valve. You will need to remove the two hoses from the cycling valve along with the AOS hose to remove the AOS.

With the turbo gone you can see the AOS unit, which includes the oil input spout (red arrow).
Figure 4

With the turbo gone you can see the AOS unit, which includes the oil input spout (red arrow). Note: we removed the cycling valve for better pictures but you do not need to remove it to replace the OAS.

The elbow hose on our project car was split almost in half (red arrow).
Figure 5

The elbow hose on our project car was split almost in half (red arrow).

Remove the heat shield (red arrow).
Figure 6

Remove the heat shield (red arrow). Once you remove the two bolts for the exhaust flange, the heat shield for the AOS will be just left lying on the engine. Simply pull it out.

Use a flathead screwdriver and loosen the hose clamp to the line on the side of the AOS (red arrow).
Figure 7

Use a flathead screwdriver and loosen the hose clamp to the line on the side of the AOS (red arrow). Leave the hose on for now, as it is easier to turn the AOS once it is undone and slip the hose off the AOS than try and force it off now.

Remove the three 13mm bolts holding the AOS to the block (red arrow).
Figure 8

Remove the three 13mm bolts holding the AOS to the block (red arrow).

Pull the AOS out from the block (red arrow).
Figure 9

Pull the AOS out from the block (red arrow).

The two seals on the AOS need to be replaced (red arrows) even if you are reinstalling the same AOS.
Figure 10

The two seals on the AOS need to be replaced (red arrows) even if you are reinstalling the same AOS.

This photo illustrates the two openings to the engine that the O-rings and AOS fit in (red arrows).
Figure 11

This photo illustrates the two openings to the engine that the O-rings and AOS fit in (red arrows). Now is a really good time to clean the block. Just make sure not to get anything into the openings in the engine. Installation is the reverse of removal.

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Comments and Suggestions:
ozzie Comments: Having changed the turbo for garret with new turbo mount with no connection for pipe on side of separator I blocked it off now have major oil leaks from this area can you advise regards Clive
April 18, 2016
  Followup from the Pelican Staff: I don't have any experience with that issue. - Nick at Pelican Parts I opened a post in our forums. A Pelican community member may be able to answer your question.
 

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