View Full Version : Oil consumption / burning? ...check this first...

04-13-2007, 04:56 PM
I didn't search enough to see if this was already covered, so apologies in advance.

Performance degradation and oil consumption increase is so gradual, perhaps minimal, that problem can go unnoticed until one day you wonder why mpg isn't as good as it used to be and oil consumption is increasing. It is easy to think engine wear, spark plugs, oil type, or some other routine maintenance item is the cause. Here's another part of the puzzle, from a fairly common issue-

If crankcase pressures get too high oil is forced into combustion chambers. Problem is caused by a malfunctioning crankcase breather (blowby) system. Breather system includes all the pipes and valves attached to the valve cover(s), plus some metal filter screens inside the valve cover. Most importantly the screen on underside of valve cover(s) condense the vapors first, and are the first to become clogged with paraffins and coked. Unfortunately, the valve cover must be removed to inspect the screen, but a quick check might provide a clue.

Quick check- If you see gunk inside the tube at the connection to the valve cover, you can bet the filter screens, various valves, and intake plenum orifices in the system need cleaning too.

Have some band clamps ready to replace the OEM ones you will remove. There are one or more plastic valves that have tiny orifices and other "guts" that might not clean up, so they might need to be replaced. If you find them to be bad, they can be replaced later, after the car is back together. The car will run no worse than it did before.

First off, the screen inside the valve cover really needs to be removed to clean it thoroughly. Not sure on the 1.8, but on the V6 the breather screens are held in place by a metal rectangle that clips onto underside of valve cover. The clips are small, but with a 90deg. pick or similar lift them up a bit to pop them off their plastic hook. I've had to do this a few times now, and have used my parts cleaner with Stoddard solvent, carb cleaner, etc, but this is what worked best by far:

To clean all this stuff including the valve covers soak overnight in a strong industrial-grade detergent like "Purple Stuff" or *my favorite* "Oil Eater" (Costco $, Home Depot $$, parts store $$$). These strong detergents will discolor aluminum, and remove paint so keep the stuff off the Audi logo and other bling. A stiff parts brush will help the stubborn deposits. Rinse with really hot water. Air dry or blow out, a little moisture left in the pipes won't matter. Detergent softens your cuticles as your skin peels off.

Some of the black plastic tubes have spiral inserts molded in to restrict flow and possibly to condense oil. Clean and rinse repeatedly until the hot water flows easily through the tubes.

On my 1997 V6 the large plastic intake plenum or duct next to the manifold had internal leaks along plastic mold lines or assembly junctions and an orange silicon flapper valve that no longer sealed. The orange flapper and some other detail might not pertain to your model year. Too much detail for this post, but suffice to say the system would not have been operating as intended, but the car still idled and ran OK. Also, there is a black plastic valve over the right valve cover that has a "Y" shape, and some one-way silicon flappers inside. After I cleared some blockage, I found that the device leaked (vacuum to atmosphere) on the small gaps around the assembly. Don't know how much if any performance is affected, but I replaced the parts anyway. The plain rubber tube at the intake manifold (vacuum source point) was loose on the hose barb.

My A4's background:

I have used Mobil1 synthetic oil, and changed at 5k-8k miles since break-in. This did not prevent issues covered above. My 1997 A4 Quattro 2.8 V6 has about 80,000 miles with obsessive maintenance, and I have found the crankcase ventilation system to be problematic in one way or another several times. Car would fall under "severe duty" category due to many short trips without reaching designed oil temp, but some problems were unrelated to usage, and are more of a design issue. Idle control valve replaced with updated unit at 50k miles.


The crankcase breather system is vital to proper engine operation and inspection and/or cleaning should be part of routine maintenance, say every 24,000 miles, more often for short trips. Fat chance any dealer maintenance is ever done on it. Not just so your Audi passes the emissions test, its proper operation affects performance, mpg, and oil consumption.

Replacing the factory set-up with plain rubber tubes (no built-in restrictors) or other aftermarket stuff may adversely affect operation and performance of the system. On the other hand, the factory components leave much to be desired and should be "bubble checked" for vacuum to atmosphere leaks.

Some "sludge" and oil consumption issues especially when over 50,000 miles might be attributable to a malfunctioning positive crankcase system.