BLOW-BY RECIRCULATION ??? What ?

[pietpetoors]

I replaced the Hilux's oil today. I bought some Shell Helix (something).
On the back of the can it says inter alia

Suitable for fuel injected petrol engines with BLOW-BY RECIRCULATION

What the heck is BLOW-BY RECIRCULATION

[Mr_B]

Hi Pieter,

In any internal combustion engine a bit of combustion gas gets by the rings, very little on a new engine, but more so on an older worn engine. These gases that enter the crank case are known as blow-by gas... on a older worn engine, where a large amount these blow-by gas and therefore pressure gets passed the rings, this would be called sump compression. All vehicles have some way or another of removing the blow-by gases from the engine, in the old days, pre 1960, the gases were allowed into the open via a breather pipe... clearly this system was not acceptable, so they developed a system by which the blow-by gases are passed back into the intake manifold to be re-burnt in the combustion cycle.... this is known as blow-by recirculation. Then in the 60's some clever people invented something called the PCV(positive crank ventilation) valve, this valve is able to regulate the flow of air in the blow-by circulation depending on engine speed.

Now the interesting question is why would they mention injectors and blow-by suitability... well with all the parts crank, pistons and conrods spinning around in the engine, an oil mist develops in the crank case... this oil mist is also passed back into the intake manifold and combustion chamber, hence why an engine with worn rings smokes and burns oil... this mist eventually collects and cakes on the intake manifold walls, this over time could be harmful for the engines fuel injectors... I would hazard a guess that this oil has some qualities that allow less of it the collect on the intake wall and some additive that minimises the oil mist in the crank case.

B

[pietpetoors]

You're a clever bloke.

The can also says that "these engines" (I presume they refer to the "Blow-by Recirculation" engines)
produce more heat resulting in more dirt and sludge to build up. This oil apparently has been "specially formulated" to clean this and prevent sludge from building up.

[Bfreesani]

I presume this is for a petrol engine. In the case of a diesel, the ultimate result of the blow-by is the replacement of the diesel inthe intake by this oil. Enough of it causes the engine to run away. It feeds it self with oil and uses it as a fuel.

Not easy to to stop an engine like that once it starts feeding itself. You lift your foot and the it keeps on accelerating . Leave it in 5th and tramp the brake till the smoke comes out the disks to make it stop. Only remedy is to go back to the 60's and release that pressure into the atmosphere.

What I did find helped, was to "T" from the tappet breather, back to the sump and to the outside. That way I could make the pressure and the vacuum you have between the top and the bottom of the piston moves the oil between these two points. There is still a certain amount that still needs to be released, but this is much less than just taking it from the tappet cover.

Oh, I feed my pressure back through the dip stick and then through a catchment bottle under the car and then to the atmosphere.

If I don't do this, my intake cakes up with that oil paste that every 25K km, I need to remove more than a beer mug of it from the inlet manifold. Just imagine what an inter cooler would look like.

[Bfreesani]

Oops, you posted that reply while I was waffling my reply.... Yip, they say that the oil soaked inlet runs hotter and in the case of diesels, retains a lot of heat compared to say an inter cooler should.

[Mr_B]

Pieter, Mr Sani...

Take a look at this thread, towards the bottom, I implemented my own blow-by breather system, which in essence filters the oil back out the blow-by gases, when the car stands for a while the filtered oil drains back down into the sump... pieter you might recognise the 'filter container' I used, it's an IFS's powersteering reservior, that's been mod'd a bit...

viewtopic.php?f=3&t=6158&start=0

Why did I do this... a high performance/high compression engine produces more blow-by gases than a standard engine, even when the engine is in perfect nic... and the PCV system simply can't cope... this mod is too rectify the issue!

B

[Mud Dog]

It's common practice to route the crank breather to the air intake directly above the carb (Not sure about fuel injection, but would imagine something similar like at the mouth of the intake manifold). I cannot imagine that it's a problem on a carb because the fuel / air mixture would clean it up, but if this is such a problem with fuel injected motors, why have they not recirculated it closer to the motor. Many inlet manifolds have vacuum take-offs of which sometimes there is one or two blanked off spares that could accept this breather pipe. If not, it would not be difficult to drill and tap a hole to fit a swage to thread nipple for this purpose which could easily be blanked off if the idea isn't successful. Perhaps on the other hand this idea would interfere too much with correct airflow meter readings and upset the EFI map? Comments?

[Mr_B]

Hi guys,

All vehicles have a blow-by recirculation system... 99% of standard motor vehicles implement a PCV valve to do the job, a pipe is connected from the tappet cover to the carb(filtered air side, no vacuum), then a second pipe, with the PCV valve inline, is connected from the tappet cover to carb(on the intake side, intake vacuum)... the intake vacuum is what creates the crank ventilation flow... this is how it is on a std 4Y and 3RZ... the only time it becomes neccesary to mod this system, is if you are running a high performance engine(high compression, high rpm) or old worn engine, that suffers with a bit of excess oil in the blow-by gases... then the std PCV system cannot cope and PCV could become clogged... which in turn lessen engine performance and shorten the lifespan of the engine oil seals(because the pressure has to get out somewhere... oil filler cap... dip stick plug... oil seals)... with my mod, the majority of the oil in the blow-by gases is returned to the sump, the intake is kept clean for longer, the injector tips are not subjected to oil vapour and carbon caking, the spark plugs remain clean for longer, and less poluting oil is burnt in the combustion cycle, therefore less carbon emissions!

B 8 )