850 oil trap - just a hollow box?

urbex · Post by **urbex** » 15 Apr 2011, 23:24

While I had the engine out, I decided now would be the best time to inspect/repair the PCV system as well. I did find the plastic hose from the oil trap to the intake hose to be broken, but the hose was pretty clean inside, as well as all the ports on the engine. Since I had intended on replacing the the oil trap anyways, I cut it open just to see what was inside.

I was quite surprised to find it was just a hollow box. Is this how it's supposed to be? I was expecting to find some kind of collection medium inside, like steel wool, or some kind of batting, considering how these things are supposedly clogged up so often. To be honest, I don't see how these things could possibly get clogged up inside, unless the engine was pushing massive amounts of oil through the PCV system, and then I'd bet that the engine had some kind of major internal wear that cleaning/replacing the PCV system wouldn't help.

My trap didn't appear as if someone had been inside it before - the seal looked like a factory plastic weld, not a glue or epoxy that was added later.

Schmitty · Post by **Schmitty** » 15 Apr 2011, 23:43

I'm not 100%, but that sounds normal. I seem to recall reading about someone being surprised the oil trap was hollow. Although I've been reading bits and pieces of every topic I can get my finger tips on, so my statement right now is not reliable (I could be thinking of something else).

Post by **Ozark Lee** » 16 Apr 2011, 07:37

A hollow box with baffles is correct. The oil comes in and the oil goes out but it allows the vapors to be bled off. It does no other filtering (thank God) or it would clog up even sooner.

...Lee

Post by **FlyingVolvo** » 16 Apr 2011, 07:46

Usually it's not the box itself that gets clogged, but instead it's all the hoses, particularly at connection points. The PTC nipple has a smaller diameter and gets clogged easily.

VolvoTurbo850 · Post by **VolvoTurbo850** » 16 Apr 2011, 16:27

It is an emission control system to prevent oil vapours (result of the oil when it heats up and the mechanical movement of valves) from escaping into the environment. If you note the pipe to that box is connected to the top of the valve main cover.

The vapour goes into the pipe and condenses, as it does this it becomes a liquid again flows down to the box. From there it flows back into the lower part of the engine to combine with the rest of the oil reserve. The box is just like a transition zone and funnel for the oil.

Quite often there is a real build up of resin on the channel where the box connects to the engine block. This in turn clogs the system and can add more pressure on the PVC system too.

Such a basic concept but I really think Volvo designed this as an afterthought because it is such a pain to get to!

MatDesign84 · Post by **MatDesign84** » 16 Apr 2011, 19:45

I see it everywhere on the forums but never asked. What is a PTC?

Post by **Ozark Lee** » 16 Apr 2011, 21:26

It is the Positive Temperature Coefficient valve. Calling it a valve is a bit of a misnomer since it is really just a tube with a heater around it. It doesn't vary the airflow at all (until it clogs up), it just heats the PCV gases up before they get shipped off to the intake system to be re-burned. It is located on the snorkel tube just before the turbo and it has a PCV line plugged into it as well as an electrical connector.

...Lee

Post by **jblackburn** » 16 Apr 2011, 23:18

Here's the little thing in question:

MatDesign84 · Post by **MatDesign84** » 17 Apr 2011, 12:29

Oh alright.