A little help needed: My 2005MY XK8 Bank 1 oil breather hose/pipe has given up the ghost due to age, heat, and general deterioration. Since an OEM replacement is no longer available in the free world market, I replaced it with an oil breather hose for a 2003 VW Passat 2.8L, which is inexpensive, has the right connections, and is almost exactly the right length. Unfortunately, it's somewhat thin-walled. Soon after installing it, the entire hose collapsed due to engine compartment heat and.... vacuum! Pulling the oil filler cap while the engine is running reveals substantial vacuum, which causes the engine to stumble until replaced. I suspect the 96,000 mile PCV valve and/or the idle air control. Working on a heavier duty breather hose/pipe, but, quick dumb question: exactly where is the idle air control located? Is it cleanable or should I just replace it along with the PCV valve? What else am I missing which could be contributing to the crankcase vacuum? Thanks to all in advance...

 

Speaking in general, the crankcase is supposed to be under vacuum. First reason is to eventually pass any type of exhaust gas making it past the piston rings into the exhaust proper (i.e. cat converters) and avoid simply releasing it and contribute to pollution. Second is less air in the crankcase to slosh around as the pistons move up and down contributes to better gas mileage. Opening the cap is letting un-metered air in the ECU has to compensate for with fuel trims. All air control operations are controlled by the ECU.

Best of luck, keep us posted.

 

Thanks fmertz; do you get the same reaction from your engine when you pull your oil cap while it's running?

How many of you note vacuum when you pull the oil cap while running, and how substantial does it seem to be?

 

Just pulling out the dipstick will cause unmetered air and make the idle stumble. At idle vacuum level is quite high as you are seeing.
To replace the line you might try auto wreckers or someone that is parting out an XK. An alternative is to get a very stiff plastic line and heat it with a heat gun and bend and form as needed. Any type of hose is just going to collapse under vacuum. Something like CPVC water line should be rigid enough and can be heat formed.

 

I have an 06 str does the same thing. No bad hoses. At idle i have 20 inches vacuum at the pcv hose. More vacuum at the filler cap means your pcv system working good as it is a sealed system. In a nutshell zero or very little crankcase pressure is getting past the pcv system. That is what you want because the leftovers from combustion are nasty and if they remain just floating in the crankcase bad things happen. I second the advice of making sure the pcv line is plastic or at the very least high grade fuel hose

 

Thanks all; obviously, I had never pulled the oil cap with the engine running before, so this was quite a surprise, as compared to all the other cars I've owned. And you're right, the breather hose has too be very thick walled or it will never hold up.

 

The material doesn't necessarily need to be thick. The early 4.0 engines use a corrugated thin plastic for the part load breather that can withstand the same vacuum. A thought occurred to me: reading the other replies. Contact one of the local industrial hose companies and give them the interior diameter and request a hose that can withstand 30 inches of vacuum. They make reinforced hoses that are capable. The x-type uses a reinforced rubber hose for the PCV connection and it draws pretty much the same vacuum.

 

Thanks; very good to know!

I learn something new every day around here...

 

that is my favorite saying with this forum

 

I can fab sell you new breather pipes/ Mine are much stouter than stock. Look for my XK8 Bible on this forum

and all the info is in there to contact me.

 

It is normal and when dealing with lean engine codes many non familiar shops look only at the intake track for faults instead of also the crankcase. Dipstick oring shrunk, bad cam cover gaskets, breather pipes, cracks in cam covers all contribute to lean air to fuel ratios.

 

yeah that dipstick o ring caused me a smog fail on my 2000 chevy truck.......crankcase system pretty much a visual....tech said against the rules to put one on but he owns the shop so did me a favor....never paid attention to the stick when checking oil...now I do