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Gary, Australia Car Mechanic
Category: Australia Car
Satisfied Customers: 1184
Experience:  Senior Technician
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Copious clouds of smoke coming from exhaust but not all the

Customer Question

Copious clouds of white smoke coming from exhaust but not all the time! can go for a couple of months with no problems then it smothers the cars behind me. Not a good look. Also the Bas light is on but that could be a faulty brake light switch? Other than that it goes well for a 240C
JA: Has the light been on for some time?
Customer: Yes several months
JA: What is the model/year of your Mercedes?
Customer: 1998 C240 Elegance with about 180k on the clock
JA: Are you fixing your C240 yourself? What have you tried so far?
Customer: Changed oil ;blocked off PVC system ;replaced valve system rubbers ; new plugs I think air filter. Used synthetic german Fuch oil.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Runs smooth very economical
Submitted: 9 months ago.
Category: Australia Car
Customer: replied 9 months ago.
Did take the sump pan off and noticed the walls of the block had crystalline carbon attached ? Maybe just normal!
had the car examined by two Mercedes workshops and they just gave up! Had a friend come up with his plug in diagnostic tool to read error codes etc. but no luck? Not sure if I flushed the oil thru with flushing oil? maybe next step! Bring on Electric cars; got an electric golf buggy and it just flies! There was oil in the throttle body and it must have been coming via the PVC system so I have blocked that off. When you pushed a finger past the butterfly valve it came out covered in oil so I thought I had the problem solved Have heard of this problem but not suggested by mechanics: then there is this sludge suggestion also not mentioned by mechanics The problem is exaggerated when pulling a vacuum i.e. going down hill, i.e. oil is being pulled into the overhead valve gear and ending up in the throttle body or simply the combustion chambers now that I have blocked the PVC system? But the engine has only done 180000 Kilometers. Don't forget I put new rubbers on the valve stems.
Expert:  Gary replied 9 months ago.

Hi there,

I would say by your description, and the results of others who have looked at your car, that you have excessive blowby from bad rings.

You could try a few things like adding a breather separator tank.

The PCV only breathes a small amount of air at part throttle compared to the larger volume in the breather hose when the engine is loaded.

This is how all the oil ends up in the throttle body and manifold.