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Roger, BMW Master Tech
Category: BMW
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BMW 740iL My 1998 4.4 BMW 740il has a lot of white smoke that

Resolved Question:

My 1998 4.4 BMW 740il has a lot of white smoke that come out of the exhaust.
Also, there is a loud noise in the engine conpartment that sounds like a horn.
When I pull out the Oil dip stick the noise stops and the oil hole where the dip stick is sucks air into the oil dipstick hole also the smoke stops everytime.
What is the problem
Submitted: 3 years ago.
Category: BMW
Expert:  Roger replied 3 years ago.

Hello,

 

This sounds like a failure of the PCV system causing high crankcase vacuum in the engine. The normal failure symptom is smoke from the exhaust but I have seen one make the noise as well.

 

The intake manifold should be removed and the rear cover on the back of the intake manifold replaced. The back cover is the PCV valve. The front cover has a gasket that will need to be replaced and the intake manifold gaskets should be replaced at the same time. Also, the intake manifold should be cleaned to remove excess oil.

 

Also for the noise, you may have to have the O ring at the dipstick tube replaced on the bottom of the dipstick. The high pressure can make the O ring get sucked down and the noise on the one that I had was from the air getting sucked through the dipstick tube where it meets the oil pan.

 

The high vacuum may also dislodge the front and rear main seal. The first step is to have the PCV replaced and then see what needs to be replaced due to the damage caused by the high vacuum.

 

I hope this information is helpful. Please press the accept answer tab. I wish you the best with your repair.

Roger, BMW Master Tech
Category: BMW
Satisfied Customers: 5821
Experience: 10 yrs. experience as BMW Master Technician, shop foreman and dealer.
Roger and 5 other BMW Specialists are ready to help you
Customer: replied 3 years ago.

Concerning the noise, when the dip stick is taken out the noise stops and your suggestion was to replace the O ring so that air can enter.

Are you sure air is suppose to enter? There were times I had a hard time pulling out the dip stick and certainly air was not entering.

 

The dip stick has always been tight and there has been no problems before, besides that is the purpose of the double O rings on the dip stick for it to be tight - am I right or am I missing something here? Once the dip stick is pulled out - air is sucked into the

the dip stick hole and the noise stops. Is this also part of the white oily smelling smoke

that is occurring because this started all at the same time. The smoke is not blueish otherwise we are talking about oil in the piston and worn piston rings but this is not the case.

 

I had taken the car to a mechanic and he suggested I may need a new engine but he would have to check it further. If he could not know immediately what the problem was I did not want any guess work so I took the car out of the shop and parked it in my garage. This is when i contacted you for advice. I've always babied my BMW it has 104K miles but runs like a new car. I drive it only on a sunny Sundays and never sees rain or snow.

 

Sorry I took long to reply, I was on a short vacation.

 

Please advise.

Expert:  Roger replied 3 years ago.

Glad to clarify.

I recommended to replace the O ring not to let air enter but to reseal the dipstick as I have seen one time that the O ring had gotten displaced due to the high crankcase vacuum. The O ring should prevent air from entering.

I would suggest smelling the white smoke. It should smell like burning oil. I have seen oil look more white than blue as it can difficult to distinguish the color. Oil will smell like burning oil, coolant would have a sweetish smell, and fuel would be an acrid smell.

I have seen this failure quite a few times and would not consider an engine replacement needed. The failure is usually the PCV plate on the back of the intake manifold. This failure can do two things. Create too much pressure or too much vacuum. Too much pressure can result in a hydrolock of oil, too much internal vacuum would create a suction and the noise you are hearing that is relieved when pulling up the dipstick.

I would recommend the dealer or someone familiar with this failure to do the repair for you but the good news is that is is very unlikely you need and engine. This is a common issue we see at the dealer.

I hope your vacation was a good one :)

Roger, BMW Master Tech
Category: BMW
Satisfied Customers: 5821
Experience: 10 yrs. experience as BMW Master Technician, shop foreman and dealer.
Roger and 5 other BMW Specialists are ready to help you

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