Breather / Catch Tank system

Competition engines and ancillaries - general discussion
Guy Croft
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Re: Breather / Catch Tank system

Post by Guy Croft »

Production engines don't use catchtanks, they have sealed breather systems that take all fumes etc back into the intake system. The emission of oily fumes to atmosphere from the crankcase would never be permitted under EU vehicle emission regulations. Turbocharged units do however have a turbocharger oil drain back to the sump.

GC
smckeown
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Re: Breather / Catch Tank system

Post by smckeown »

Guy Croft wrote:I have exp in this area - on engines working well and badly!

Sorry to cut right across this but no way do you need a drain back to the sump. I have never fitted nor recommended this in my life. Firstly because on an engine where the catchtank is located above the breather vent and which has good ring sealing because there shouldn't be much by way of oil in the tank - ever. A catchtank is really there to allow oil vapour to condense - the droplets are tiny so you shouldn't get much by way of accumulation. So you're stopping them blowing to atmosphere (or over the racetrack).

On a good engine you can get a lot of oil going to the catchtank - straight up the breather hose - and not just vapour - in high G if the sump isn't well baffled or - if the sump is overfilled. Or if you have an accumulator and hook it up wrong it overfills the sump and never draws off. On an engine that's in trouble you can get oil thrown out if a bearing is badly worn. And, naturally, an engine with poor bore-ring sealing is going to chuck oil out all the time.

One reason for not draining the catchtank is that you can get a pretty good idea of how the engine is running by examining the amount collecting in it.

GC
Thanks for your input Guy. I will do more testing then before taking it any further. I believe my catch tank may have been to low, which may have encouraged the tank to full up on 2 occasions.

I'll do more specific testing to ascertain which breather is causing the output, and in what conditions
205 8v Track car
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