Diesel crankcase vent

[team karst]

I have a kubota 10 hp diesel on board. I notice when i attempt to vacuum out hot dirty oil that unless the oil filler cap is removed, no oil flows. I find it odd to not have crank ventilation to atmosphere. Normal?

[pcmm]

Originally Posted by team karst

I have a kubota 10 hp diesel on board. I notice when i attempt to vacuum out hot dirty oil that unless the oil filler cap is removed, no oil flows. I find it odd to not have crank ventilation to atmosphere. Normal?

If the engine has a PCV valve as part of the crankcase ventilation, then yes that would be normal. a PCV valve only allows ventilation OUT of the crank case.

It is however normal to open the oil cap when you are doing an oil change. No different than on a car.

[team karst]

Originally Posted by pcmm

It is however normal to open the oil cap when you are doing an oil change. No different than on a car.

Gosh. This is the first motor that required oil cap off. Ive done decades of oil changes on a wide variety of cars. Weird

[pcmm]

Originally Posted by team karst

Gosh. This is the first motor that required oil cap off. Ive done decades of oil changes on a wide variety of cars. Weird

You'll still get the oil out as long as the tube for the extractor doesn't seal against the dipstick tube. And yes if you open the oil cap on a car, the oil will drain a lot faster. I see it all the time (in fact every time, for decades) when I change my oil in my truck, it flows a lot faster with the oil cap removed!

[Iron E]

Originally Posted by pcmm

You'll still get the oil out as long as the tube for the extractor doesn't seal against the dipstick tube. And yes if you open the oil cap on a car, the oil will drain a lot faster. I see it all the time (in fact every time, for decades) when I change my oil in my truck, it flows a lot faster with the oil cap removed!

True... less glug

[skipperpete]

Originally Posted by team karst

Gosh. This is the first motor that required oil cap off. Ive done decades of oil changes on a wide variety of cars. Weird

Hi team karst. Are using a large diameter suction hose over the outside of the dip tube or a thin tube down the inside of the tube ?
I can understand how not opening the filler cap would foil your efforts to suck out the oil if you do the large hose method rather than the capillary, I have a Kubota powered genset with the dip tube going into the very lowest point of the oil pan, the dip tube IS the extraction tube so little to no hope of air entering the crankcase with the cap on.

[rslifkin]

I've never had an engine where the crankcase was sealed so tightly that oil wouldn't drain without the cap open. On most engines with a PCV system, there's either a fresh air return to the crankcase to allow flow-through while the engine is running, or the crankcase ventilation allows air to enter when the engine is shut down.

[skipperpete]

On a multi cylinder engine with a large internal volume and 4 sets of piston rings to leak you might not have a suction problem but the OP has a 10hp single cylinder engine, not much internal empty space but the same physical extraction rate. It occurred to me that the vac pump might also be a bit off its game too. At least there’s an easy fix.... take off the filler cap.

[team karst]

Its a twin cylinder with a factory equipped rubber hose going to the bottom of the oil pan; the end of which is plugged when in service. It will not drain until the oil cap is off. Only a vacuum results internally. Its not an issue to remove the cap, but it raises a question in my mind in crank ventilation, ability to eliminate internal pressure buildup during operation.

I can pull all the oil out of both my volvos using a factory provided steel tube going to pan sump; in about 30 seconds of vacuum, a gallon of oil is in the discard tank. Oil caps still installed and suction hose sealed over the engine tube. On these motors the valve cover has a feature to connect the valve train with the filtered intake air passage. There cannot be crankcase pressure buildup.

[skipperpete]

Sorry team karst, I assumed single cylinder. If it’s a Z482, here’s where to find the PCV valve and where it vents into.

[team karst]

Here is mine.


You can see the valve cover with the oil fill cap and a small hose running to the air inlet duct/ intske manifold. Maybe hidden magic inside.

Both pix show valve covers with a square flanged feature on top.

[Iron E]

Originally Posted by rslifkin

I've never had an engine where the crankcase was sealed so tightly that oil wouldn't drain without the cap open. On most engines with a PCV system, there's either a fresh air return to the crankcase to allow flow-through while the engine is running, or the crankcase ventilation allows air to enter when the engine is shut down.

Diesels don't have PCV Systems. At least not the ones I've had.

[rslifkin]

Originally Posted by Iron E

Diesels don't have PCV Systems. At least not the ones I've had.

They usually have some kind of crankcase ventilation. Some are a PCV type setup to the intake (doesn't necessarily involve a traditional PCV valve though). Some are just an open breather. It varies a lot. But I've never seen an engine of any size where you can pull a vacuum on the crankcase with the engine shut down (but I have seen some that are designed to pull a slight vacuum while running).

[Iron E]

Originally Posted by rslifkin

They usually have some kind of crankcase ventilation. Some are a PCV type setup to the intake (doesn't necessarily involve a traditional PCV valve though). Some are just an open breather. It varies a lot. But I've never seen an engine of any size where you can pull a vacuum on the crankcase with the engine shut down (but I have seen some that are designed to pull a slight vacuum while running).

I see, so crankcase ventilation.. I come from automotive field, not diesel, but I've seen PCV mentioned in this thread, so I was a little puzzled.
Thanks

[rslifkin]

Originally Posted by Iron E

I see, so crankcase ventilation.. I come from automotive field, not diesel, but I've seen PCV mentioned in this thread, so I was a little puzzled.
Thanks

PCV just means positive crankcase ventilation. So any setup that forcibly sucks air out of the crankcase would count as PCV. On a diesel you wouldn't need a PCV valve to limit flow, as you're not dealing with high intake vacuum like on a gas engine.