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Diesel engine blow-by?

R

Roy W

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Location
N. Ireland
Car
Accord CDTi Sport
Hi all,

This has alarmed me how much blow-by i have on my `07 ctdi engine (74,000). I removed the oil filler when it was ticking over only to get splattered with oil and fumes. In saying that it runs normally, uses no oil and mpg is around 47-50...... but i find new oil goes black only after a few days.

What do you think folks?
 
you removed the oil filter housing with the engine idling????

AFAIK it is normal for the oil to turn black sooner than that on a petrol. One of the purposes of oil is to extract the crap from the engine so as its turns black, it is doing its job. Regular oil changes along with filters will keep the engine good, and try not to remove the oil filter housing again with the engine on. Definately not a wise thing to do.
 
No, i said `filler` (filler cap) not filter............ ! :huh:

It`s the pressure/blowby in the crankcase that has alarmed me...............
 
Roy as saj said the oil will turn black as soon as you turn the key. as for the filler cap im not sure about a diesel but i always fault this was a sign of back pressure
 
Theres no need to remove the filler cap while engine is running, as you say youll end up with pulsating oily air coming out. And yes there is lots, and its why in racing they have dry sump oil systems. from a touring car for example, they can gain 30bhp from removing the wet sump as on all of our cars and using dry sumping. Some of that gain is removing that negative pressure that the crank and pistons have to fight.
 
Why on earth would you remove the oil filter (the cap and the filter are the same thing as the paper element sits inside cap).

It's not blow-by, it's simply the high pressure of oil being pumped around the engine in a sophisticated modern turbo charged engine.

I think you need to be more concerned with your own actions rather than a perceived fault in your engine.
 
Roy said:
No, i said `filler` (filler cap) not filter............ ! :huh:

It`s the pressure/blowby in the crankcase that has alarmed me...............
Click to expand...


my bad, didnt read it properly. Still, best not to open either of them eh?, whilst the engine is running of course
 
pleeease people reread my first post!! I said FILLER cap not filter cap :rolleyes:

hopefully as f6had says its just the nature of the beast and not that any rings have gone or worse......
 
Clearly I need to get to Spec Savers... having said that, I still think it's a daft idea to open any cap that exposes the internals whilst the engine is running!
 
obviously Roy is old school and others just don't know here on old engines you took the oil FILLER (NOT filter) cap off and if the piston rings are Donald then you would have a lot of fumes coming out the filler cap because of blow by past the pistons but on new engines with crankcase breathers etcetera it doesn't show up quite as much
 
On our Ford Dorset's in the boat we call it breathing, the rocker cover has a pipe fitting to allow the "blow by" to escape, we catch the residue in a bottle. There are no breathers on your honda only the system that reburns these vapours back through the engine, they put the screw cap on the rocker box to make sure it stays there, instead of the old fashioned bayonet fitting. That's why you should not "screw" around with it whilst the engine is running!!
 
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