300tdi- Blow-By or Faulty Vacuum/Brake servo?

LeftFoot · Apr 16, 2019

Greetings,

Can someone explain to me the link that exists between the vacuum pump/brake servo and crankcase pressure?
In other words, is it possible to have symptoms of "blow-by" due to a faulty vacuum system?

Why I am thinking it is the vacuum system:
1. I took head off to replace head gasket 2 weeks ago and found nothing unusual. Gasket was in fairly good condition still. Valves seemed ok in guides, replaced valve seals, cleaned carbon from valves and lapped them before reinstallation. Whilst head was off cylinder bores had no discernible scores or marks in them. They were actually very smooth and clean. Head was level tested and passed. No compression test was done yet though...

2. Engine shouldn't be worn in my estimate, it has just passed 95,000 miles.

3. Exhaust smoke is visible at idle constantly. Light grey in colour. Clearly visible at night in headlights of vehicles behind.

Is it possible the vacuum system could be responsible?

Gmacz · Apr 16, 2019

I would look at injectors first. Get them tested.

Al2O3 · Apr 16, 2019

LeftFoot said:
Greetings,

Can someone explain to me the link that exists between the vacuum pump/brake servo and crankcase pressure?
In other words, is it possible to have symptoms of "blow-by" due to a faulty vacuum system?

Why I am thinking it is the vacuum system:
1. I took head off to replace head gasket 2 weeks ago and found nothing unusual. Gasket was in fairly good condition still. Valves seemed ok in guides, replaced valve seals, cleaned carbon from valves and lapped them before reinstallation. Whilst head was off cylinder bores had no discernible scores or marks in them. They were actually very smooth and clean. Head was level tested and passed. No compression test was done yet though...

2. Engine shouldn't be worn in my estimate, it has just passed 95,000 miles.

3. Exhaust smoke is visible at idle constantly. Light grey in colour. Clearly visible at night in headlights of vehicles behind.

Is it possible the vacuum system could be responsible?

No.
Could you see honing marks, helical scores, on the walls of the cylinders?
Are you using oil?
What colour is the smoke in daylight?
When did you last change your air filter?
Do you still have the EGR valve fitted?
Is you turbo in good nick?
You don't actually explain how the vacuum system could be causing the exhaust smoke.

LeftFoot · Apr 16, 2019

Al2O3 said:
No.
Could you see honing marks, helical scores, on the walls of the cylinders?
Are you using oil?
What colour is the smoke in daylight? Light grey
When did you last change your air filter? Air filter is less than 3 months old.
Do you still have the EGR valve fitted? No.
Is you turbo in good nick? To be further determined. No excessive play at fins.
You don't actually explain how the vacuum system could be causing the exhaust smoke.

Could you see honing marks, helical scores, on the walls of the cylinders? As mentioned above cylinders are smooth and clean.

Are you using oil? Not anymore than the usual leaks.

What colour is the smoke in daylight? Light grey/blueish.

When did you last change your air filter? Air filter is less than 3 months old.

Do you still have the EGR valve fitted? No.

Is you turbo in good nick? To be further determined. No excessive play at fins.

You don't actually explain how the vacuum system could be causing the exhaust smoke.

In my understanding excess "blow by" results in oily vapour accumulating in rocker assembly at pressure. The cyclone breather cannot fully cope with removing the oil from the vapour resulting in a lot of it making its way to the turbo intake. This in-turn circulates and builds up in the intake system and eventually burns and results in a smoky exhaust.

tottot · Apr 16, 2019

Sound's like the bore's are glazed [ smooth and clean] resulting in some blow by into the crankcase. Vacuum pump would have nothing to do with this.

LeftFoot · Apr 16, 2019

tottot said:
Sound's like the bore's are glazed [ smooth and clean] resulting in some blow by into the crankcase. Vacuum pump would have nothing to do with this.

It is never good news is it? Thanks, that makes sense. Milege is indeed low and it makes many short trips so that diagnosis fits.

tottot · Apr 16, 2019

When I put a 200 in my 1990 TD it was from a 90 tdi that had spent its time poodeling about launching and recovering boats from the sea [it was a total rot box ]
Motor only had about 80k on it and used about a ltr of oil per month. I just used it giving it the work it needed like towing loaded trailers and getting thrashed on the way to Coastguard call out's. Over time it has improved with little smoke and oil use.

300tdi- Blow-By or Faulty Vacuum/Brake servo?

LeftFoot

Active Member

Gmacz

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Al2O3

Well-Known Member

LeftFoot

Active Member

tottot

Well-Known Member

LeftFoot

Active Member

tottot

Well-Known Member

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