Should there be pressure under the rocker cover?

[Argos69]

Hi all,

Work has prevented me messing around with my 2017 Berlingo Multispace Flair 120 since I bought it around November. It has stood idle due to lockdown and now I'm able to use it, thought I'd give it the once over.

When I take off the oil cap when the engine is running, there is quite a "blow" from under the top cover..... It smells oily (but then it would wouldn't it?). I can't ever recollect noticing this on any previous Berlingo.

As I once said to the doctor - "Is this normal?". The car has done 21000 miles.

Thoughts and opinions welcomed. The car is under Citroen warranty at present.

Thanks

[Argos69]

Pretty quiet......

If nobody actually knows, is there any chance some kind person could go and whip off their oil filler cap when their engine is running, just to see if it "blows" or "sucks"....?

Thanks  

[saskak]

Pretty quiet......

If nobody actually knows, is there any chance some kind person could go and whip off their oil filler cap when their engine is running, just to see if it "blows" or "sucks"....?

Thanks  

It is inevitable that there will be some crankcase pressure, cylinders do not seal perfectly. I have no experience with the 2017 model, but there is crankcase pressure on the 1.6HDi 2007 model (M59) and it blows from the oil filler cap. How much? It will depend on the amount of blow-by. With 21,000miles covered, it should be less than one that has covered more, but it is difficult to compare with other engine models, e.g. the older 1.6HDi.

[RobS]

As said all engines have crankcase pressure due to piston blow by. This can be higher on new engines and reduce as the rings bed and then increase as they become worn. Time depends on servicing and such like. Modern machining is better than in the old days so the running in time is now reduced. But the inclusion of things like EGR are now actually increasing wear rates. 

The real test is lubricating oil consumption. Assuming there is not any leaking out on the floor if you don't have to top it up after a 1000 miles more than a 1/8 Litre it's still pretty good I would say. This is not a manufactures recommendation just my observation after 50 years driving.

[Gryffindor]

I did read but couldn't offer any useful advice. All I can suggest is if the oil system has no venting, then because solids and liquids expand when they get hot, logically speaking, I would expect some pressure. The water system has an expansion tank, no doubt for a similar reason.

[RobS]

I did read but couldn't offer any useful advice. All I can suggest is if the oil system has no venting, then because solids and liquids expand when they get hot, logically speaking, I would expect some pressure. The water system has an expansion tank, no doubt for a similar reason.

It vents into the engine inlet and any oil mist is burnt in the cylinders. Venting to atmosphere was banned years back.

[saskak]

As said all engines have crankcase pressure due to piston blow by. This can be higher on new engines and reduce as the rings bed and then increase as they become worn. Time depends on servicing and such like. Modern machining is better than in the old days so the running in time is now reduced. But the inclusion of things like EGR are now actually increasing wear rates. 

The real test is lubricating oil consumption. Assuming there is not any leaking out on the floor if you don't have to top it up after a 1000 miles more than a 1/8 Litre it's still pretty good I would say. This is not a manufactures recommendation just my observation after 50 years driving.

Good points there. I should have said pistons rather than cylinders.
I think the accepted (according to Haynes) oil burning (1.6HDi; M59) is <500ml per 1,000 miles, which is ridiculously high. I never had to topup oil between oil changes on my 2007 1.6HDi, but 1/8 seems acceptable.

[Argos69]

Thank you all for your input. Much appreciated.

I suppose I just remembered back to the days of my Escort MkII where they introduced a wee mesh-filled "filter" between the rocker cover and inlet manifold, to suck the evil crankcase fumes into the engine as an antipollution measure. This gave a fair vacuum and meant no more rocker cover gasket oil leaks - however bad that gasket was!

The same car suffered from "running on" when switched off, so Ford fitted a simple solenoid air bleed valve and tube going to the inlet manifold, fed from the ignition. When it was switched off there was a whoosh of air and no more running on.
Simple, but I do recall driving through a town when my 1300 engine suddenly surged forward and the revs shot up!. After I stopped and put the bonnet up I found the wire had dropped off the solenoid allowing air to rush in to the manifold!
A lovely unintended "boost" feature from Ford!

Still, can't be too harsh on them. It was a car I could maintain with just a Gunson's Colortune and a timing light! Ah, sweet memories....