300Tdi Engine Breathing Theory

Al2O3 · Jun 25, 2017

My engine rebuild is burning oil and it looks like most of it is going through the intercooler.
Anyway, it's got me thinking about the pressures in the air intake, rocker box etc.
I'm getting a bit of pressure/chuffing out of the oil filler hole.
When the engine is running and so pulling air through the air filter and through the intake pipe to turbo, this must also be pulling on the pipe from the cyclone breather? So, this must mean there is negative pressure through the cyclone. How do I feel positive pressure out of the filler cap? There must be a greater pressure differential in the rocker cover than is pulling through the cyclone. Presumably, when the turbo spools up, it's be sucking harder through the cyclone? There must be a reasonable amount of resistance caused by the air filter, so once the turbo is pulling hard might it be pulling more air through the cyclone than through the air filter? I Haven't had cause to contemplate this before. @Brown mentioned a valve in the TD5 breather pipe, but I'm sure the 300Tdi doesn't have one. What does this valve do?

Brown · Jun 25, 2017

What I've got in the TD5 breather system is one of these:
http://www.ebay.co.uk/itm/LAND-ROVER-DISCOVERY-2-TD5-DEPRESSION-CONTROL-VALVE-/220852421089

There's some discussion of what it does here:
https://www.landyzone.co.uk/land-rover/td5-breather-pipe.147895/
and here:
http://workshop-manuals.com/landrover/defendertd5/emission_control/crankcase_emission_control/

But I've never had a 300 TDi so not sure what they have. There's some discussion of this in relation to the Discovery:
https://www.landyzone.co.uk/land-rover/300tdi-crankcase-ventilation-valve.109528/ but I don't know if the Defender has anything similar.

Al2O3 · Jun 25, 2017

Brown said:
What I've got in the TD5 breather system is one of these:
http://www.ebay.co.uk/itm/LAND-ROVER-DISCOVERY-2-TD5-DEPRESSION-CONTROL-VALVE-/220852421089

There's some discussion of what it does here:
https://www.landyzone.co.uk/land-rover/td5-breather-pipe.147895/
and here:
http://workshop-manuals.com/landrover/defendertd5/emission_control/crankcase_emission_control/

But I've never had a 300 TDi so not sure what they have. There's some discussion of this in relation to the Discovery:
https://www.landyzone.co.uk/land-rover/300tdi-crankcase-ventilation-valve.109528/ but I don't know if the Defender has anything similar.

Cheers, Brown. I've read through those links and it looks like my theory is correct. There seems to be a lot of hassle caused by excessive oil going through the cyclone and in to the intercooler etc. No-one seems to know why. It'll be interesting to see what compression results I get.

raywin · Jun 25, 2017

It used to be the story that diesels used a bit of oil for the first few thousand miles, I remember a friend getting a vauxhall and they told him not to worry.
I think yours might be a bit high but pressure tests will give some idea. My understanding of the breather system is just to vent any blow by from the pistons which then picks up oil on its way out just because the sump and rocker case are absolutely full of oil mist. Many years ago this went through a cap with a wire wool pad in it to coless the oil and allow it to drain back into the rocker case. Nowadays emission standards have gone up and the vapor is vented to the intake of the turbo which you will find has a slight negative pressure dependent on turbo speed where it is fed to the engine and burns harmlessly with the diesel charge.
Odd that you are getting such a good MPG if compression was down then efficency should suffer but yours is running so sweet. Might be interesting if you could give it a good long run and then re check the oil consumption before doing anything drastic.
The cyclone oil trap should show little resistance to flow in the port from engine to turbo inlet.

Al2O3 · Jun 25, 2017

raywin said:
It used to be the story that diesels used a bit of oil for the first few thousand miles, I remember a friend getting a vauxhall and they told him not to worry.
I think yours might be a bit high but pressure tests will give some idea. My understanding of the breather system is just to vent any blow by from the pistons which then picks up oil on its way out just because the sump and rocker case are absolutely full of oil mist. Many years ago this went through a cap with a wire wool pad in it to coless the oil and allow it to drain back into the rocker case. Nowadays emission standards have gone up and the vapor is vented to the intake of the turbo which you will find has a slight negative pressure dependent on turbo speed where it is fed to the engine and burns harmlessly with the diesel charge.
Odd that you are getting such a good MPG if compression was down then efficency should suffer but yours is running so sweet. Might be interesting if you could give it a good long run and then re check the oil consumption before doing anything drastic.
The cyclone oil trap should show little resistance to flow in the port from engine to turbo inlet.

I suppose it might get less smokey over time, but the oil consumption is way above what I'd expect. So, I think there must be more to it than just waiting for it to 'run in'.
Yeah, the mpg figures are hopeful, but I need to repeat them a few times yet to get a reliable average.

300Tdi Engine Breathing Theory

Al2O3

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Brown

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Al2O3

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raywin

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Al2O3

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