Diesel Breather Hose Question

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Diesel Breather Hose Question

Post by David »

Hi all, I have been doing some more leak busting on my bx because frankly I am sick of oil dripping from everywhere, Anyway I have repetitively found oil on the black air box that screws on top of the engine. (it is the 1.9 diesel).

I have concluded it must be going up the breather hose that connects to the oil filler/ dipstick housing and running all over the air box, So the question is: can I simply block the breather off or is it needed? It has 2 other breathers on it, one goes to the engine block, fairly low down & one goes to the rocker cover. This pipe I have just replaced as it was cracked. I don't understand why it would need this other breather going to the air box, and it looks like it has a valve of some sort on it anyway, but I don't know what it is for, or if its just how it clips to the air box.

Any thoughts?
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Re: Diesel Breather Hose Question

Post by rutter123 »

hi David. all breathers are there for a reason i wouldn't block any up or this could cause too much pressure in the block and blow a seal or worse. If you have a good motor factor nearby they should be able to supply the sizes of rubber pipes and reducers,connectors, elbows etc to make up something like the original, i have done this recently on the t/d with good results.
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Re: Diesel Breather Hose Question

Post by Tinkley »

The purpose of the breather to the air box is reburning crankcase emissions to meet whatever legislative target was applicable at the time. Same with petrols too btw. When the engines get old and a bit tired they can produce more crankcase pressure giving more oil mist which then gets reburnt. On my 1.4 petrol I used to get gobs of mayonnaise straight into the main jet whilst doing 70mph resulting in the engine stopping... Once I discovered this, I rerouted the pipe to atmosphere and plugged the feed to the air box. I can't see why you can't do the same, BUT you may have to revert it back for MOT time... :wink:

My old Morini (1977) used to vent direct to atmosphere through a pipe with a baffle in it. Later ones had to put the breather into the first stage air box for the carbs.

Worth cleaning out all the wire gauzes in the system first though especially oil filler cap one.

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Re: Diesel Breather Hose Question

Post by Dragon Man »

its like the EGR of early diesels.. you can buy things called oil catch tanks that can be bolted or tie wrapped to somewhere in the engine bay. you then feed the pipe into that and vent the pipe coming out of the box to atmosphere.

just a note though, diesel crank case gasses smell horrendous. (and they are much worse in the newer common rail diesels!) venting to the air box or just after is just an easy way of getting rid of the bad smell and any oil drips it may give out.
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