CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Negative crank case pressure

Greetings
I have a 2006 BMW X5 that I purchased new and now has 52,000 miles on it. I received an offer in the mail from a repair shop that specializes in BMW and other European cars, to receive a free “autologic” check of my X5. There was no check engine light or any indication that something was wrong, I just wanted to see if they could find something wrong and I made an appointment for the car. I returned 3 hours later and was told that the engine had negative crankcase pressure and that they would have to “dig into it a little more” and wanted to keep it overnight as it may mean bad valves. The cost would be $400.00 for removing the intake manifold and if any valves were bad it would cost up to $4000.00 more to repair the valves. I left the car overnight and went home and checked with a couple of friends that have some car knowledge and then I called another repair shop, told them what was going on and asked them for their opinion. The second shop told me that 95% of BMWs operate with negative crank case pressure. The next morning I went back to the first shop, told them not to do anymore work and took my car home. Was the second repair shop correct? The car is running fine.

Wayne

@trojan1959 not to sound too pessimistic, but it sounds like that “autologic” shop was using the old scare tactic to drum up business.

“Get 'em in in the door with the free inspection and then hit 'em hard with the laundry list of needed repairs.”

Perhaps you should ask around about the autologic shop. Maybe somebody has firsthand experience dealing with them. It all sounds strange.

I would suggest you wave to the shop if you ever pass by in the future.

The PURPOSE of the PCV system is to develop and maintain negative crankcase pressure…You WANT negative crankcase pressure…These guys are fishing for your WALLET…

“. I returned 3 hours later and was told that the engine had negative crankcase pressure and that they would have to “dig into it a little more” and wanted to keep it overnight as it may mean bad valves.”

This borders on criminal activity, I wouldn’t let them TOUCH my lawn mower…

You were being scammed. Your engine has a PCV valve in it, as do ALL cars from ALL manufacturers sold in the US since 1964. The job of the PCV valve is to create a little negative pressure in the crankcase so that is sucks any oil vapors back into the combustion chamber to be burned completely.

If your engine didn’t have negative crankcase pressure, it would have a problem. You would probably be burning a lot of oil then.

+1 to Caddyman and keith!

While I believe that BMW refers to their PCV system by some name other than “PCV”, as was stated, your car–like all cars made since 1963–needs to have negative pressure in the crankcase in order to draw-off the “blow-by” fumes that were vented to the atmosphere prior to the advent of PCV systems.

It is clear to me that this shop preys on people with little or no automotive knowledge, and by tossing around bogus terminology that might sound scary to the uninitiated, they probably rope-in a lot of business that is pure profit.

As was also said, you should definitely avoid this shop in the future as they are not to be trusted.

I wasn’t sure about it but I thot you should have negative crankcase pressure.

They will look into it, charge the $400, replace whatever part they feel like changing and charge $150 for it if you let them. They need the parts changing practice.

Probably one of those shops who think that if you can afford a beemer, you can afford to be ripped off.

There is a subtle point in these replies which I disagree with, which is that your engine would have problems if it didn’t have “negative crankcase pressure”.

Up until 1963, engines ran fine without PCV systems. It was a simple and inexpensive method for preventing engine blow-by fumes from going into the atmosphere.

Your engine’s performance is independent of whether its blow-by fumes are vented freely to the atmosphere or redirected back to the intake manifold.