removing oil cap whilst engine is running

bigjl

Standard auction test, though always funny to watch the private auction buyers do it when not knowing exactly why, then looking in the hole and sometimes getting an oil shower.

WaxDaddy

Gloomendoom wrote: »

I still disagree. The air is sucked into the induction system via the crankcase ventilation system. The crankcase is normally sealed to keep the nasty oily vapours in. Any positive pressure generated in it is relieved by the crankcase ventilation system which sucks the crankcase air into the induction system (normally at a point between the MAF and the throttle or any supercharger). If you take the oil cap off then the crankcase is open to atmosphere and fresh(ish) air is allowed in. From there it gets sucked into the induction system. The MAF is bypassed and as a result more air enters the cylinders than the ECU knows about. The engine will then run lean.

Where have I gone wrong?

If there is positive pressure inside the crank case, as there almost always will be, air will not enter it. Simple.

the crank case is vented to the intake so that the vacuum pressure can suck air out, or via a catch tank and then the intake.

I've been building engines for years and done the test that buyer did many many times and never known it make a difference to how the engine runs nor have i ever known it cause a problem.

cyclonebri1

bigjl wrote: »

Standard auction test, though always funny to watch the private auction buyers do it when not knowing exactly why, then looking in the hole and sometimes getting an oil shower.

So is that the test for a private auction buyer, oil stains from the bonce downwards??? ;);), Only joking, (maybe)

Gloomendoom

WaxDaddy wrote: »

If there is positive pressure inside the crank case, as there almost always will be, air will not enter it. Simple.

the crank case is vented to the intake so that the vacuum pressure can suck air out, or via a catch tank and then the intake.

I've been building engines for years and done the test that buyer did many many times and never known it make a difference to how the engine runs nor have i ever known it cause a problem.

Interesting.

What do you think caused the OP's car engine to start whirring and wheezing when the oil cap was removed?

cyclonebri1

Consider the fact that in a worn engine the excess presure will avtually force air into the intake system, remove the cap and the pressure is removed and the engine runs "differently", and I have had some crap engines in my time, :rotfl:

Gloomendoom

I think the problem would be exacerbated if the air filter was clogged and in need of replacement... so it might indicate that the car needed servicing.

cyclonebri1

Gloomendoom wrote: »

I think the problem would be exacerbated if the air filter was clogged and in need of replacement... so it might indicate that the car needed servicing.

Ok, but removing the rocker filler would reduce the air bypassing the filter as it would remove the positive pressure in the intake.

It's all plausible but bottom line it indicates a less than perfect6 "injun" ;);)

Gloomendoom

cyclonebri1 wrote: »

Ok, but removing the rocker filler would reduce the air bypassing the filter as it would remove the positive pressure in the intake.

It's all plausible but bottom line it indicates a less than perfect6 "injun" ;);)

I disagree

But I can't be arsed to go through it all again.

cyclonebri1

Gloomendoom wrote: »

I disagree

But I can't be arsed to go through it all again.

I think the point we differ on is the fact that the engine is designed to breath in a certain way, but as it wears it cannot, hence the theory and what happens eventually in practice. Thats why the bloke took the cap off, ie to check the state of wear

Kilty_2

Sounds like a new breed of tyre kicker to me :rotfl: