I've got a 85' 300CD with what looks like a smaller than usual pre-filter, set between the oil filter housing and brake booster. I haven't seen it in any manual or 'how to' on the web. The pre-filter is were I expected but I found thing lil' guy hiding in the back.
Commonly done. It's nothing more than a filter to prevent oil from the vacuum pump being sucked into the system if the pump starts to fail or leak. Good visual indicator of a pending pump failure if you see oil in it, too.
It does no such thing. Its a fuel filter, its deigned to pass oil through. It only serves as a visual indicator of a failed shutoff actuator diaphragm.
Ok. So its a small inline fuel filter acting as a 'vacuum line filter'. If i wanted to replace it what size or special type(?) should I be looking for?
Pretty much. I have also used spare inline (diesel) fuel filters when I had a surplus of them. They just need to be able to pass vacuum and nothing more.
I've done this on most of my diesels over the years, as it gives you an immediate visual indication of an impending vacuum pump failure, and also helps to prevent damage to the vacuum system and brake booster from oil.
That's ingenious. I never thought of doing it. Going to tomorrow.
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