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[veralum]

I have oil on the inlet manifold and believe it is from where the throttle body joins the inlet manifold, but why would there be oil there? I have checked and cleaned the breather pipes and they were unobstructed. Any ideas

[Doctor Gollum]

It's a thing. When the engine is running hot oil vapour from the crankcase is drawn into the engine via the breathers, two channels on the breather bridge vent just ahead of the throttle body, and are combusted.

Once the engine is switched off, these vapours condense and drip down into the intake duct and the plenum, resulting in the oil you see.

It’s perfectly normal. And as an addition to the annual breather clean, the intake ducting should also be removed and cleaned. You may find upto a centimeter of oil at the bottom of it. 

[veralum]

Cheers

[Doctor Gollum]

Apologies, I misread your title...

Four pot is a different breather set up, but the principle is the same. 

The oil ends up pooled in the inlet manifold rather than the intake trunking as on the V6 due to the different configuration of the components. The four pot throttle body is mounted vertically so as the vapour condenses, it drains straight down into the intake manifold. The V6, by contrast has a horizontal throttle body, so the condensed vapour drains away from the plenum rather than into it.

In theory, once the engine warms up, the oil that has collected in your manifold will turn back into vapour and be burnt off as part of the combustion process, (this is less so on the V6 because the intake trunking where the oil collects is plastic and not directly attached to the block).