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Crankcase pressure reference values?
#1
Hi All,

Does anyone know what the reference values (new engine) are for the crankcase pressure on the 1.6HDi (DV6ATED4; M59; no fap/dpf)?

Since installing an oil catch can (https://www.berlingoforum.com/thread-18041.html) I wanted to check if it has any effect on the crankcase pressure. Managed to find some guidelines from a Mini and the crankcase pressure should be <50mbar, but this is rather vague. I have concocted a tube coming out of the oil filler cap hooked to a digital manometer and a quick measurement (at idle) shows max ~11mbar, which seems acceptable. Nevertheless, the pressure somewhat fluctuates from ~ -10 to ~ +11mbar. I am also a bit puzzled by this fluctuation. I am not too sure, but it could be the CCV burping the crankcase gasses/pressure out, but I thought this should be more stable.

Of course I will compare my catch can install pressure measurements against the original air intake pipes, so it is not a problem to know if there is an increased pressure. I just wanted to know the crankcase pressure reference values in general, in order to see how my engine compares.

Many thanks for any info on this.

Cheers,
saskak
smile, you are alive!
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#2
Hi All,

My digital manometer that I bought (https://www.amazon.co.uk/Digital-Manomet...B07CLCTGQW) appears to be defective.

I reported that the crankcase pressure measured by the manometer was fluctuating from ~ -10mbar to ~ +10mbar. I decided to check it with the old school technique, i.e. made my own manometer. I cut ~3m of clear tubing (8mm internal diameter), made a U-bend, stuck it to a plasterboard and filled with water about half of the tubing.

At idle, there is ~7mm of crankcase pressure and it is not at all fluctuating, pretty steady. If I rev the engine, vacuum appears, I could not quite see, but probably 7mm or thereabouts. Unfortunately the plasterboard with the tubing was in front of the car and I was inside. The vacuum is pretty steady, even if I further increase the rpm, the vacuum stays constant. That is to be expected, the CCV (CrankCase Ventilation) valve is doing its job to limit the vacuum that the air intake manifold is producing. i.e. not to suck crankcase oil into the intake manifold (pre-turbo).

At least I know that the oil catch can works as it should be, but might have to source smaller diameter tubing. There is not enough resolution in my tubing with the 8mm diameter. Clearly the pressure/vacuum is not enough to push water of 8mm diameter. My physics is a bit rusty, but will try to calculate the pressure in inches of water or mbar.

If I manage to properly calculate the crankcase pressure, I will report back for future.

Here is my manual manometer:    


Cheers,
saskak
smile, you are alive!
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#3
OK, made some quick calculations, although might be off somewhere. BTW, in a U-bend manometer the diameter of the tube makes no difference, only the density of the liquid.

What I derived is ~1.35mbar of pressure at idle and ~1.35mbar of vacuum (higher rpm). AFAIK the CCV valve in diesels is supposed to keep relatively constant pressure in the crankcase and slightly above atmospheric pressure at idle and just below atmospheric pressure under load (a slight vacuum or negative pressure). Of course if there is more blow-by (worn engine) then the pressure will be bigger as the CCV cannot open more. I would appreciate if anyone knows the reference values for the 1.6HDi (M59; DV6TEDA4).

At idle, there is little vacuum at the air intake manifold and just the pressure from blow-by (~1.3mbar), so CCV is open to relieve the pressure. At higher rpm, there is negative pressure or vacuum at the air intake manifold and the CCV slightly closes the opening to reduce this negative pressure and that is ~1.3mbar.

Measurements were taken from the oil filler cap. Might be wrong in my explanation, as I have not considered the vacuum pump. These are also fairly quick calculations, so might be off with a 0 somewhere and my measurements have quite a bit of an inherent error. Even 0.5mm is ~7-8% error in the measurement.

Cheers,
Saskak
smile, you are alive!
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#4
Interesting stuff, thanks for the write up. IIRC, the crankcase vacuum is needed to stop pressure build up behind the various oil seals so the limited amount of vacuum you found would be all that's needed, any more and excessive oil vapour would be pulled through the turbo. I think the vacuum pump on the 1.6HDi is only connected to the brake servo & turbo actuator?
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#5
(24-04-2019, 06:51 AM)cancunia Wrote:  Interesting stuff, thanks for the write up. IIRC, the crankcase vacuum is needed to stop pressure build up behind the various oil seals so the limited amount of vacuum you found would be all that's needed, any more and excessive oil vapour would be pulled through the turbo. I think the vacuum pump on the 1.6HDi  is only connected to the brake servo & turbo actuator?

The vacuum or negative pressure might be slightly bigger than 1.3mbar. I could not quite see the water in the polytube from inside the car, but using the eyeballing technique, it is about there. At idle my measurement is relatively more accurate. I will make a smaller manometer, one that I can hold in the car and measure again. I think the digital manometer might be playing up a bit, the hot air from the crankcase could make it inaccurate and unstable. It is only designed to operate up to 50C.
You are probably right about the vacuum pump.
smile, you are alive!
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#6
Hi All,

In case anyone is interested in crankcase pressure/vacuum. I made a smaller DIY manometer and measured the crankcase pressure at idle with a vernier caliper. The error rate is relatively small. The overall crankcase pressure on my engine (1.6HDi; M59; ~92,000 miles) is ~1.37mbar.

Under sustained load and with an increase in rpm, there is an initial vacuum (negative pressure) that is short-lived, i.e. ~0.5-1sec. Then the crankcase pressure reverts to positive pressure, but slightly less than under idle. The CCV (CrankCase Ventilation) valve will have reduced the opening, so the source of the vacuum (air intake) has less effect on the crankcase pressure.
There is a sustained vacuum (negative pressure) only when coasting (gas pedal not pressed) in gear, e.g. downhill.

I also made some measurements and the oil catch can does not result in an increased crankcase pressure. I compared (at idle) the crankcase pressure with an oil catch can and with the original pipes and there was no difference. There was no measurable difference with my apparatus, there could still be a few percentages difference.

If you want to see the measurements at idle and higher rpm here are the manometer measurements (end of video): https://www.youtube.com/watch?v=FZYWcqkMN-I
smile, you are alive!
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