Hi guys and gals,
On my 1999 Mk2 1.8i BP4W engine, I have 2 breather pipes, one either side of the cam cover. The one on the driver’s side of the engine (the left hand side looking from the front of the car) goes via a non return valve to the inlet manifold. The one on the passenger side (the right hand side looking from the front of the car) goes to the air intake/induction pipework leading to the throttle valve and is connected to that pipework after the MAF unit.
Can anyone explain this system please? I’m assuming that the metered flow of air through the intake/induction pipework to the throttle valve causes a ‘suction effect’ on the right hand side breather and that in effect puts the engine crank case under a negative pressure overall, thereby 'sucking out any blow by gases back into the intake to be burnt off. If this is correct, how does the left hand side breather work especially with the non return valve in it? Is this a type of relief valve should the crankcase ever go under positive pressure?
I’m asking these questions a) because I’m an old fart and I like to know how things work and b) I was thinking about removing the right hand breather pipe all together and fitting one of those small breather filters that look like a miniature K&N cone filter (obviously plugging off the connection to the intake/induction pipework as well). Also, I was thinking of installing an oil catch tank into the left hand side breather pipework but obviously I need to understand how the original Mazda system was designed to work first.
Sorry this is a bit long winded, I hope I’ve explained it properly
Best Regards to you all and Happy driving…
Tony
Other way round, the crankcase gases are drawn into the intake manifild though the one way valve, the valve is opened by manifold depression.
I’m not sure of the purpose of the pipe on the exhaust side on the engine. I’d guess it’s either to prevent the build up of crankcase pressure when the PCV valve is closed or to allow fresh air to enter the crankcase as the crankcase gas is drawn out. There should be no negative pressure in the crossover tube as it’s upstream of the throttle butterfly. Fitting a breather to the exhaust side of the system would, I think mean that the crankcase gas entering the intake manifold would be unmetered air entering the engine, as the air being sucked in though the filter wouldn’t have passed through the air flow meter as it would have done if it was taken from the crossover tube.
Hi Robbie, thanks for that.
So basically, if I did use one of those small filter things on the exhaust side, the engine would in effect get a mix of metered air from the intake and unmetered air from the engine breather via the crankcase. This would therefore lead to a more ‘leaner’ air/fuel mix than normal as the ECU would only be picking up the metered air side and adjusting the amount of fuel injected accordingly.
Best I leave things as they are then eh?
Regards
Tony
The unmetered air thing in just my opinion, many people fit breather filters with no problems at all I think.
I believe it is now illegal to vent any engine breather to atmosphere. Try removing the oil filler cap with the engine ticking over, it should stall due to the mixture being too lean. Unless the ECU is very clever and compensates for this. I think your decision to leave well alone is well advised, I know that is what I would do. There is some good reason for the breather being fitted in the infitite wisdom of Mazda.
Regards Geoff Peace.
Regards Geoff Peace.
Hi Geoff,
Yes, I am leaving it as Mazda intended. I was only looking at fitting a breather filter to add a bit of ‘bling’ to the engine. I’ve seen many engines with these filters fitted but I don’t want to damage my engine in any way which is why I asked the original question. With the help of Robbie, I now know the breather theory and am leaving things as they are…
Thanks for your interest…
Regards
Tony
really??
what are you surposed to do when you have a turbo?
or does venting to atmosphere mean without going through a filter?
Hi Tony
If you fit one of those small filters on that side of the engine you will have oil dripping all over the place.
I have Jenvey throttle bodies fitted, with an Adaptronic ecu running these beauties, the inlet side breather is blocked off, the exhaust side breather is piped into a collection tank (750cc), which has to be emptied about every 750-1000 miles depending on how hard youve driven it, so you could see your problem there.
Roger Hawkins
99 MK2 Classic Red
Thanks Roger,
The last thing I want is oil all over the place… so I’m going to leave as Mazda intended.
Cheers for the info…
Regards
Tony
Engines nowadays are supposed to be a sealed system, any gases from the crankcase are vented into the inlet manifold by some means or other. The petrol tank etc. is also sealed, hence the charcoal canister. All to do with the “emissions” I am told!
Regards Geoff Peace.