Yellow goo? What to do.
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The 2 main things that contribute to yellow goo are cold running engines and/or short trips in very cold weather. Note this is not a VW specific issue/problem, it happens on many cars both import and domestic.
I see you are located in Rochester, NY, I know many of our Canadian friends also have this quite often.
Very helpful DIY, however, in addition to cleaning, you really need to do the following.
1. Verify your engine coolant temperature and make sure you are not suffering from a soft failing thermostat that is causing the engine to run colder than normal. The only way to verify the engine coolant temperature is to use some sort of scan tool that can read and display real time data.
The expected coolant temperature in these cars should run between 200-205F consistently. If you find the engine running cooler than 200F consistently, you have a thermostat that likely has a weak spring and needs to be replaced.
You cannot rely on the ECM to trigger thermostat codes as this is a very unreliable way to verify coolant temperature. I had a bad thermostat in my 1.8t that was running 20-25+ degrees too cold and it never trigger the CEL or a code for a coolant temperature problem.
The good news is once you have a tool that can read the coolant temp, it is really a either the thermostat is good or it is bad decision. There is really no discussion about it.
It is important for your engine coolant temperature to be correct in order for the engine oil to get warm enough to fully "cook" off water vapor/condensation and excess fuel in the crankcase. Just be aware it takes the engine oil 2 to 3 times longer to get up to operation temperature than the engine coolant. If your engine is running cold, it make take the engine oil between 3-5 times as long to come up to temperature than coolant. Not sure if the 2.0L has the oil cooler like the 1.8t, but the oil coolers are actually somewhat of an asset during cold weather operation as they are actually an oil warmer as well as an oil cooler, so there is some dual benefit for the oil cooler if the engine is equipped with one.
2. If you find your engine temperature is operating in the proper range and you still have yellow goo, you need to evaluate your driving distance and driving style and possibly include a longer drive that includes a fair amount of highway driving. Doing this once or twice a week to really get your crankcase temperature up to a good operating level is a wise thing to do on a regular basis.
I see you are located in Rochester, NY, I know many of our Canadian friends also have this quite often.
Very helpful DIY, however, in addition to cleaning, you really need to do the following.
1. Verify your engine coolant temperature and make sure you are not suffering from a soft failing thermostat that is causing the engine to run colder than normal. The only way to verify the engine coolant temperature is to use some sort of scan tool that can read and display real time data.
The expected coolant temperature in these cars should run between 200-205F consistently. If you find the engine running cooler than 200F consistently, you have a thermostat that likely has a weak spring and needs to be replaced.
You cannot rely on the ECM to trigger thermostat codes as this is a very unreliable way to verify coolant temperature. I had a bad thermostat in my 1.8t that was running 20-25+ degrees too cold and it never trigger the CEL or a code for a coolant temperature problem.
The good news is once you have a tool that can read the coolant temp, it is really a either the thermostat is good or it is bad decision. There is really no discussion about it.
It is important for your engine coolant temperature to be correct in order for the engine oil to get warm enough to fully "cook" off water vapor/condensation and excess fuel in the crankcase. Just be aware it takes the engine oil 2 to 3 times longer to get up to operation temperature than the engine coolant. If your engine is running cold, it make take the engine oil between 3-5 times as long to come up to temperature than coolant. Not sure if the 2.0L has the oil cooler like the 1.8t, but the oil coolers are actually somewhat of an asset during cold weather operation as they are actually an oil warmer as well as an oil cooler, so there is some dual benefit for the oil cooler if the engine is equipped with one.
2. If you find your engine temperature is operating in the proper range and you still have yellow goo, you need to evaluate your driving distance and driving style and possibly include a longer drive that includes a fair amount of highway driving. Doing this once or twice a week to really get your crankcase temperature up to a good operating level is a wise thing to do on a regular basis.
Thanks for your reply, jfoj.
First of all, the 2.0 does have an oil cooler, so this should be helping warm the oil in cold weather. And I do agree the thermostats do get weaker over time and don't keep the engine as warm as it should be. But I think this phenomenon is largely driven by the ambient air temperature. The vent housing and ventilation hose are kind of "up in the breeze" and stay cold.
I had been watching my rear main oil seal leak for a couple of years before I cleared out that ventilation hose. That means that it was plugged for two summers. During summer my vent housing is completely clear of the goo. So apparently the ventilation hose will not clear by itself.
Ironically, the presence of the goo could be an indication of a well-maintained engine. A worn engine with leaking piston rings would have a higher airflow through the crankcase and be less susceptible to the goo.
First of all, the 2.0 does have an oil cooler, so this should be helping warm the oil in cold weather. And I do agree the thermostats do get weaker over time and don't keep the engine as warm as it should be. But I think this phenomenon is largely driven by the ambient air temperature. The vent housing and ventilation hose are kind of "up in the breeze" and stay cold.
I had been watching my rear main oil seal leak for a couple of years before I cleared out that ventilation hose. That means that it was plugged for two summers. During summer my vent housing is completely clear of the goo. So apparently the ventilation hose will not clear by itself.
Ironically, the presence of the goo could be an indication of a well-maintained engine. A worn engine with leaking piston rings would have a higher airflow through the crankcase and be less susceptible to the goo.
One thing you could try and see if it helps the situation is bit it try to find some of the split foam pipe insulation and cover the rubber hose that connects to the oil fill cap.
It is hard to tell if the size of the vent hose, but if is is close to 3/4 inch, this should be pretty easy except for the bend, but you cold also cover it with foil tape?? Other manufacturers do offer insulated crank case ventilation hoses.
Question about cleaning out the vent hose, did you find hardened goo in the pipe after the Winter season?
It is hard to tell if the size of the vent hose, but if is is close to 3/4 inch, this should be pretty easy except for the bend, but you cold also cover it with foil tape?? Other manufacturers do offer insulated crank case ventilation hoses.
Question about cleaning out the vent hose, did you find hardened goo in the pipe after the Winter season?
The standard hose is somewhat thick and soft, so it does have some insulating properties. I'm thinking of trying to make some kind of extension to the upper engine cover to try and keep the ventilation system warmer.
The goo never really hardens. The first time I cleaned the hose I pushed a waded paper towel through it. Most of what came out was still soft. The inner wall did clean up pretty well.
The goo never really hardens. The first time I cleaned the hose I pushed a waded paper towel through it. Most of what came out was still soft. The inner wall did clean up pretty well.
Head gasket is a possibility, but not likely the usual situation.
Yellow goo or Mayo as I call it is a common issue with German and other cars in the colder Winter months due to shorter trips, weak thermostats and the oil/crankcase not getting up to temperature to "cook" off any moisture and water vapor that ends up in the crankcase. The engine oil usually takes about 2x as long as the engine to fully warm up, you likely need a minimum of 20 minutes drive time to get the oil up to a good, stable operating temperature. Buy you likely need 30+ minutes of driving with some higher speeds to really evacuate the crankcase. Many drivers have short trips and commutes that just kill the oil with moisture.
I also speculate that the Ethanol fuels that absorb more moisture also contribute to this issue a bit as well.
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I get the yellow goo/mayo on both our New Beetle and on my '91 Crown Victoria (the Pontiac Vibe doesn't get it). On the '91 Crown Victoria, I believe it's caused by an extra long oil filler neck which extends from the valve cover and is capped with the oil cap. The extra long neck likely keeps it from heating up in the winter, so the yellow goo/mayo is worst in the winter.
In the summer, the problem is much less noticeable.
In the summer, the problem is much less noticeable.
It seems like most of the 2.0 engines in colder climates experience a buildup of a gooey yellow or brownish substance under the oil cap in the winter. Wiping it up with a paper towel shows that it is actually mostly water. It is created by the combination of oil vapors and water condensation in colder portions of the crankcase volume.
I believe that the root cause is the inadequate design of the crankcase ventilation system for this engine. Every other car I have owned used a pair of crankcase ventilation hoses; one between the valve cover and the air filter box to supply clean air to the crankcase and another from the valve cover to the PCV valve. Air is drawn out of the crankcase through the PCV valve and into the intake manifold. Since there are both an air inlet and a vacuum source, a constant flow of air takes place.
With the 2.0 engine there is a single ventilation hose and there is no conventional PCV valve. The single hose runs from the vent housing under the oil cap to the air intake boot near the inlet to the throttle body. At the air intake boot there is a reed valve that allows flow in one direction: out of the crankcase and into the intake boot. The reed valve in combination with the natural air pulses at the throttle body will create some vacuum, similar what is provided by a PCV valve. However, without a way for air to get into the crankcase the only air flow in the crankcase comes from the blow-by combustion gases that get past the piston rings. Water vapor is a major combustion byproduct, so not only is there very small airflow through the crankcase, but what there is contains a lot of water vapor. As a result there is a lot of condensation at the coldest point in the crankcase volume, which is the vent housing and ventilation hose.
So, it looks like we will have to live with the yellow goo. Does it do any harm? Well I found that my ventilation hose was completely plugged with the goo. In fact, if there is much goo visible under the oil cap then it is likely the ventilation hose is plugged. After I cleared out the ventilation system I found that an oil leak that I had assumed was from the rear main oil seal completely stopped! The plugged hose allowed pressure to build up in the crankcase which pushed oil out the main seal or perhaps the vent housing/valve cover joint and then down the back of the engine. An overpressurized crankcase can cause driveability problems as well.
Here is a DIY that I put together on how to clean out the goo:
1. Remove the engine cover using a 10 mm wrench. Here is a photo of the ventilation system components that you will find underneath:
![Auto part Product Pipe Engine Fuel line]()
A - Vent housing.
B - Ventilation hose.
C - Intake boot.
D - Reed valve housing.
2. Use pliers to squeeze the clamp securing the ventilation hose to the reed valve housing and slide it down the hose. Remove the end of the hose from the reed valve housing.
3. Twist the vent housing clockwise about 45° and lift it up to remove from the valve cover. It attaches like an oil cap, but twists in the reverse direction. Here is a photo of the assembly about to be removed from the valve cover:
![Auto part Fuel line Engine Carburetor Exhaust manifold]()
4. Remove the oil cap, clamp and hose from the vent housing. If you had any amount of goo visible under the oil cap the chances are the ventilation hose will be completely full with it. Here is a photo of the disassembled parts:
![Auto part]()
5. Clean the goo out of the vent housing and the ventilation hose by gently tapping them on a piece of cardboard or newspaper. The goo, being partly oil, is very slippery and easily comes out just with tapping.
6. Inspect the hose to make sure it isn't cracked or damaged. If it needs to be replaced I recommend a genuine VW part as the aftermarket ones tend to be made of really cheap material and don't last.
7. Reassemble in reverse order.
The procedure may need to be repeated every few weeks during cold weather. The condition of the ventilation system can be monitored simply by removing the oil cap and inspecting for a buildup of the goo.
I believe that the root cause is the inadequate design of the crankcase ventilation system for this engine. Every other car I have owned used a pair of crankcase ventilation hoses; one between the valve cover and the air filter box to supply clean air to the crankcase and another from the valve cover to the PCV valve. Air is drawn out of the crankcase through the PCV valve and into the intake manifold. Since there are both an air inlet and a vacuum source, a constant flow of air takes place.
With the 2.0 engine there is a single ventilation hose and there is no conventional PCV valve. The single hose runs from the vent housing under the oil cap to the air intake boot near the inlet to the throttle body. At the air intake boot there is a reed valve that allows flow in one direction: out of the crankcase and into the intake boot. The reed valve in combination with the natural air pulses at the throttle body will create some vacuum, similar what is provided by a PCV valve. However, without a way for air to get into the crankcase the only air flow in the crankcase comes from the blow-by combustion gases that get past the piston rings. Water vapor is a major combustion byproduct, so not only is there very small airflow through the crankcase, but what there is contains a lot of water vapor. As a result there is a lot of condensation at the coldest point in the crankcase volume, which is the vent housing and ventilation hose.
So, it looks like we will have to live with the yellow goo. Does it do any harm? Well I found that my ventilation hose was completely plugged with the goo. In fact, if there is much goo visible under the oil cap then it is likely the ventilation hose is plugged. After I cleared out the ventilation system I found that an oil leak that I had assumed was from the rear main oil seal completely stopped! The plugged hose allowed pressure to build up in the crankcase which pushed oil out the main seal or perhaps the vent housing/valve cover joint and then down the back of the engine. An overpressurized crankcase can cause driveability problems as well.
Here is a DIY that I put together on how to clean out the goo:
1. Remove the engine cover using a 10 mm wrench. Here is a photo of the ventilation system components that you will find underneath:
A - Vent housing.
B - Ventilation hose.
C - Intake boot.
D - Reed valve housing.
2. Use pliers to squeeze the clamp securing the ventilation hose to the reed valve housing and slide it down the hose. Remove the end of the hose from the reed valve housing.
3. Twist the vent housing clockwise about 45° and lift it up to remove from the valve cover. It attaches like an oil cap, but twists in the reverse direction. Here is a photo of the assembly about to be removed from the valve cover:
4. Remove the oil cap, clamp and hose from the vent housing. If you had any amount of goo visible under the oil cap the chances are the ventilation hose will be completely full with it. Here is a photo of the disassembled parts:
5. Clean the goo out of the vent housing and the ventilation hose by gently tapping them on a piece of cardboard or newspaper. The goo, being partly oil, is very slippery and easily comes out just with tapping.
6. Inspect the hose to make sure it isn't cracked or damaged. If it needs to be replaced I recommend a genuine VW part as the aftermarket ones tend to be made of really cheap material and don't last.
7. Reassemble in reverse order.
The procedure may need to be repeated every few weeks during cold weather. The condition of the ventilation system can be monitored simply by removing the oil cap and inspecting for a buildup of the goo.
Make sure the engine is running at the proper temperature, typically 205F. Then make sure you do not make a lot of short trips in the Winter/colder months.
Attempt to get at least 1 good 45+ minute drive in a week.
Then "manage" the mayo/goo.
When coming home for the end of the day, try to warm the engine well, then remove the oil fill cap for the evening to allow the crankcase to vent/breath overnight.
Just make sure to reinstall the oil fill cap in the morning before you drive off.
Attempt to get at least 1 good 45+ minute drive in a week.
Then "manage" the mayo/goo.
When coming home for the end of the day, try to warm the engine well, then remove the oil fill cap for the evening to allow the crankcase to vent/breath overnight.
Just make sure to reinstall the oil fill cap in the morning before you drive off.
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