2.0T Oil Consumption Issue: PCV & Carbon Buildup

Gear case (3)Their is no way to make this long story short to explain 2.0T oil consumption. Bear with us. It used to be that intake carbon deposits were 90% caused by low quality fuel. In the case of the TFSI motors, the story is different. We poll our customers at Karmakanix to get to the bottom of every issue that we can. Most of the carbon issue customers report using high quality fuel from the filling stations that talk about their additives and cleansers. So a different explanation for high carbon issues is afoot. The carbon diagnosis and cleaning procedures are on a separate webpage. FYI: PCV Breather Valve is synonymous with Crankcase Pressure Valve, Breather Valve or PCV Valve.

Many of our 2.0T customers report high oil consumption when we query. The problem usually stems from the PCV (Positive Crankcase Ventilation) system, specifically from a set of crankcase breather valves where the rubber is thinner than a bicycle inner tube. They can seep. When the PCV valves leak full on, the engine idles poorly, the mixture readings in Measuring Value Blocks (MVB’s) are way off, one or more codes are set, and the check engine light is on. The dealer will deal with that if the vehicle is still under warranty. PCV leakage basically means that the PCV breather valve is broken. One sign is that the oil cap can be removed while the engine is idling with no effort at all, or that the oil cap cannot be removed due to intense vacuum in the crankcase. The PCV breather valve on a 1.8T or 2.0T EA888 engine incorporates 2 check valves, a pressure valve, a bypass valve and a PCV valve. The net effect of a failure on crankcase pressure / vacuum depends on which valve or combination of valves failed inside the PCV breather valve. If you have a PCV valve that seeps, the engine operates normally, but you will have a 2.0T oil consumption issue, and your engine will be building up carbon at a high rate.

To be clear, PCV leakage is not the problem that causes 2.0T oil consumption, PCV seepage is the problem. The PCV system has two functions: Keep the crankcase from pressurizing under boost, and keep the intake system from sucking more than slightly on the crankcase. When one side PCV breather valve seeps, the crankcase goes under excessive vacuum during deceleration or at idle and the intake vacuum sucks the oil out of the motor. Proof of the problem is one cannot easily remove the oil cap while the motor is running. When the other side PCV breather valve seeps, the engine crankcase goes under pressure when the turbo goes into boost mode. That pushes oil around the rings, but the big effect is different. The turbo’s tiny crankcase normally drains excess oil into the engine’s crankcase. The turbo does not have positive oil seals, just some tiny devices akin to tiny piston rings, plus a splash plate like an old bug motor crankshaft. Positive oil seals would never survive the 90,000 to 130,000 rpms of a wound up turbocharger. When the engine crankcase goes under pressure, so does the turbo crankcase, which then pushes oil out of its tiny crankcase along the shaft and into the intake and exhaust systems. Proof positive is to take off the intercooler hoses. If the intercooler has a lake of oil inside, the PCV seeps.

So what is the normal pressure in an engine crankcase? That depends on the engine speed and load, and varies with altitude and engine wear. Each engine is designed with different pressure parameters to control emissions as well as oil consumption. On the 1.8T and 2.0T EA888 Generation 3 engines, the pressure control valve inside the PCV breather valve is rated for a difference of -100 millibar (-1.45 psi or 2.93 “Hg) relative to the ambient air pressure. On a normal engine at idle, that will be the approximate negative pressure (vacuum) measured at the oil cap. The pressure will change slightly while driving. It can go slightly positive under load as the blow-by gases get redirected from the intake manifold to the turbocharger inlet. The crankcase should never experience either a high vacuum or a high pressure.

We freely admit to speculating on one issue. Sounds a bit odd to talk about the quality of PCV gases, but we may have found a connection between fuel quality and intake carbon, and it may be minor, but we are not sure. In earlier cars before stratified fuel injection with injectors mounted in the intake manifold, fuel quality is the huge difference in carbon issues. In fact engines that use high quality fuel build up almost no carbon at all. Low quality fuel always results in carbon, and the results are more about the driver’s habits. A purely city driver will experience a significant carbon problem in 4 to 7 years for sure. It does make sense however that if the combustion and its residues are cleaner, so must be the blow-by gases that escape past the pistons into the crankcase. Since those gases are coming back out through the PCV breather valve and into the intake, the carbon issue could be less of a problem while using high quality fuel. The life of the PCV breather valve material might be better as well, not having to be exposed to higher levels of more obnoxious gases that result from burning poor quality fuel. Just a thought, may be almost nothing……

The PCV oil and gases, and any oil misted from the turbo, get sprayed into the intake manifold and onto the valves. Because the injectors are not mounted in the intake manifold, there is nothing to wash the debris off the valves. That debris becomes the carbon that will start to cause serious engine misfires and eventually will cause the car to be undrivable. Please see our page on Carbon Cleaning and Diagnosis for a complete explanation.

Another valid concern is the long term effect on the catalytic converter of the vehicle. Manufacturers are quick to point out that when an engine is over filled, the cat can get damaged from the excess oil. So what happens to the catalytic converter with a tiny amount of oil is being burned consistently by a motor? The effect of burning oil is known to affect cat life, but only very slightly with normal oil usage. It is unclear at what level the hydrocarbons and clinker have a measurable effect at the customer level, but it is likely to be very minor. But some minerals and metal compounds can “poison” the precious metal substrate of a catalytic converter. A list of cat contaminants includes lead, sulfur, manganese (gasoline additive MMT), silicon (from coolant), phosphorus and zinc. Although current SAE standards limit phosphorus content in engine oil, certain high mileage oil blends and certain additives may contain phosphorus and zinc antiwear additives such as zinc dithiophosphate (ZDDP). Making any confident statement could be fallacious, but it is certainly likely that an engine that burns 5 to 10 times as much oil as another may have a shorter lived catalytic converter.

We cannot overstress the importance of 2.0T oil consumption in a TFSI or TSI motor. Even when the PCV breather valve is still under warranty in a newer car, the dealer will not help you with oil consumption issues unless you can prove that your engine uses over 1 quart per 1500 miles. They will help you ascertain the oil consumption with a visit every two weeks. Unless there is a code for the PCV, which only happens when it leaks badly, the dealer will not get started. They will happily charge you to look at the problem. The carbon problem will eventually happen, and the more oil is consumed, the faster the carbon builds up. Ask about their cost for decarbonization near the beginning of the conversation.

So one may well ask: How much oil consumption is acceptable with a 2.0T engine? Last century, a good running motor consumed between 1/2 to 1 quart every 5000 miles. These 2.0T engines in good condition use about 2 quarts per 5000 miles. At Karmakanix, we highly suggest that if a 2.0T engine uses more than a quart every 2000 miles, one should replace the PCV breather valve assembly. It might be a good idea just to replace it every 100,000 miles.

2.0T Crankshaft Seal Failure

Another unhappy element to the 2.0T oil consumption story is the sudden failure of the crankshaft seal on the transmission end of the engine. One might wonder what relationship this failure might have with the crankcase PCV breather valve. We find that a 2.0T engine that has spent some time running with a damaged breather valve may end up with a damaged crankshaft seal. The seal is made unlike traditional seals in that is a very thin PTFE (Polytetrafluoroethylene, like Teflon) ring glued onto the sheet metal seal housing. What happens is that a failed breather valve allows the crankcase to pressurize while driving under load, and/or the crankcase gets high suction while decelerating or idling. The thin crankshaft seal flexes and either splits or detaches at the glue joint.

Generally oil leakage from the crankshaft seal failure and/or a check engine light is the first obvious sign. The possible DTC codes include: P0171 System Too Lean, P0300 Random Misfires, and P2279 Intake Air Leak. It is pretty much guaranteed that if the crankshaft seal started leaking violently, the breather valve failed first and damaged the seal. Occasionally the crankshaft seal fails either immediately after or within a mile or two after the PCV breather valve is replaced. The transmission and flywheel/clutch or flexplate must be removed to get to said crankshaft seal.

The factory now sells a revised seal that is pressed into place instead of glued on to the sheet metal seal carrier. Some aftermarket crankshaft seals have sprung up that have manufactured the older style aluminum seal carriers with replaceable seals to fit the 2.0T engines. Those seals are not PTFE type seals, but synthetic rubber with a tensioner spring, an older and proven design. Karmakanix has chosen to use the updated factory seals.

2.0T CAEB Extreme Piston Wear

It needs to be mentioned that some of the later 2.0T engines driven by timing chains have a very rare problem with defective pistons. So far, the culprits seem to be the CAEB engines produced between 2009 and 2011. In those motors, the oil consumption issue seems to get worse in a short period of time. Generally the problem becomes noticeable between 50,000 and 80,000 miles, and within 10,000 to 20,000 miles becomes extreme. By extreme we mean the engine burns a quart of oil every few hundred miles. Audi has warrantied a piston replacement job for many of these cars, but now most are long out of warranty. Karmakanix has the piston replacement procedure sorted out.

The piston problem seems to have a number of etiologies. One finds reports of broken rings and pistons on the internet. We have only really encountered extreme wear caused by insufficient wrist pin diameter. The wrist pin is the bar that connects the rod to the piston and forms the pivot point as the piston rises and falls. When the wrist pin diameter is small, the tendency and force for the piston to rock back and forth is higher. And when wear begins, the rocking motion gets exacerbated rapidly, and the piston actually wears to a slight oval shape. The replacement pistons and rods have a wrist pin that is larger, and the problem does not seem to recur at all.

There is a machining note to mention. It has always been common practice to hone the cylinders of a block when replacing the piston rings in any cast iron block, so as to have a fresh surface for the rings to break in correctly. It is accepted however that this ring job is performed without honing. The crankshaft has a timing wheel on it that would get destroyed if honing was attempted. The job to remove the crankshaft prior to honing is rather time consuming due to the new main bearing cradle support having a set of bolts from the sides, the presence of piston spray jets that would need to be removed, and the three sets of chains and oil pump on the front of the engine. The new rings seem to break in well, based on the reports that the job repairs the oil consumption issue.

2.0T Carbon Cleaning and Diagnosis

After all just said, one might think that we should just go straight to cleaning out the carbon when one of these cars come in with a misfire. Actually, no; as further diagnosis is required. A fair amount of misfire problems end up being due to spark plugs or coils. About a quarter are misfiring due to mixture or injector issues. A few have been damaged motors. The carbon problem is often found in conjunction with other misfire causes, but is a primary cause about one third of the time.

An engine that misfires cold, but not warm is often a sign of an impending carbon problem. Strong evidence comes in the form of a code for intermittent cylinder disabling, when the ECU shuts off the fuel and spark to a cylinder to stop extreme knocking / pinging. The explanation is complicated, please continue to our webpage on Carbon Cleaning and Diagnosis.

Gear case (2)Karmakanix Knowledgebase on Carbon Diagnosis and Repair Procedure

Gear case (3)