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Why do I need a filter on the crankcase breather? - Engine/Ancilliaries - The Lotus Forums Jump to content
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Why do I need a filter on the crankcase breather?

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If I am just venting the crankcase to the atmosphere, why do I need a filter on the hose? Seems to me that the crankcase will never have negative pressure. Also, if i do vent to the atmosphere will pressure build up in the crankcase under high load?

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I guess you may get negative pressure under throttle 'lift off' conditions if your rings or valve/guides were not sealing perfectly? (The opposite condition of worn engines blowing their dipstick out) Question 2 - No, but you will potentially get crap all over the place as the vapourised oil/steam etc condenses - Steve

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I think as the hot engine cools it will start to suck in. You only need a little bit of grit to be sucked in and it could block on oil way etc. Its a bit like leaving your sandwiches out on the side. Nothing should get to em but would you leave me out all day? hahahah

Buddsy


 

"Belief is the enemy of knowing" - Crrow777

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Have you read up on this on the LEW site. The perceived wisdom is that if you dangle the breather tube down under the shield it is highly unlikely that anything would get sucked up that far. Filters are no longer added since they can get clogged and then this restricts the fumes exit.

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I think the idea of the filter is to catch the oil as it comes out like the wire mesh in the oil filler cap on old Mini engines. If you have a dry sump car, the scavenge pumps could pull a vacuum (racing engines usually run a vacuum in the sump to reduce aerodynamic drag on the crank).


S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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Hi,

Just add an oil catch tank, very cheap and simple, also means oil does not end up on the road and you can fit a filter aswell, best of both worlds.


A

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Make sure the pipe to the catch tank is big enough in bore dia. I think its surprising how much pressure can build up. Someone on here fitted one too small and I think the pipe got blocked causing pressure to build up in the crankcase. This then blew the dipstick out along with a lot of oil too!! I am planning to fit a catch tank myself though. Im sure with a bit of thought it should be ok.

Buddsy


 

"Belief is the enemy of knowing" - Crrow777

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