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Early this morning I embarked on a 2-hour road trip with my trusty 2001 1.8T (110K miles) across rural Illinois to attend a meeting. Initially the temperature was about 5F -- nothing unusual for this winter. As I got away from the suburbs, the temperature started falling: 0, -5,-15,-19F. I was happily cruising along the interstate at 70mph and hit the gas to pass a slow truck. The engine spooled up normally and the tranny downshifted twice. At some point I suddenly noticed whistling, as if from the turbo. Did I blow a turbo on that high speed pass, I wondered? It definitely has a new sound, and the pitch varies with throttle, just like the big rig diesel turbos. It never did THAT before. After another 20 minutes I noticed the engine was struggling to accelerate up the next on ramp. I must really have blown the turbo, I thought. Should have been more gentle to this aging car on that last pass. Before long I was barely able to maintain 40mph on the side roads. Oh man, this repair is going to be expensive. Damn, this car better get me to the nearest town. I don't want to be stranded in the middle of farmland at -19F out of range of a cell tower! Eventually I reached a small town at a top speed of 25mph. I finally made it to the post office, at which point the engine would not accelerate in gear. Then engine speed slowly dropped to zero. DEAD! At no time did the CEL come on. The engine would crank and fire but not run up to idle. Now what? I sat for a few minutes, made a phone call, collected my things and got ready to seek out warmth. Maybe 10 minutes had passed and I decided to crank one more time. It started and held idle. Interesting. I let it idle for a few more minutes, got brave, revved it up, put it into gear and drove away with full power as if nothing had happened!:)

So what DID happen? :confused: I guess the recycled crankcase vapors (which contain water vapor from combustion blowby) formed ice inside the intake manifold and never had a chance to melt and vaporize as long as minus 19F air was rushing in. Only by shutting down the engine and letting the residual heat defrost the intake manifold was it possible to unblock the air system. Has this happened to anyone?

Later in the day on the return trip after about an hour of driving I noticed some reduced performance and the reoccurrence of the whistling, but to a much lesser degree this time. The temperature now had risen to 2F, which may have been warm enough to prevent total icing.

I wonder if all Passats have this weakness? For sure there is no need for the intercooler during the winter. Probably should put a cover over it the next time I take a long trip. ///
 

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Strange. These cars are routinely driven in all sorts of temperatures. Even Canadian winter temps. I don't know what happened to cause your symptoms. The unusual turbo noise is a good clue but I don't know what it means. At first I would suspect a blown intake path hose but that wouldn't repair itself. Something icing up is a possibility.
 

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Very odd; I know that small airplanes have a "carb heat" function specifically to prevent this issue on airplanes, but I've never heard of it happening on a car.
 

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Engine with carburetors would need a "hot spot" to prevent ice forming right under the throttle body, but injection cars don't have that problem. I can't think of a problem that will cause what OP described.
 

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If you're traveling at extended lengths with any vehicle in sub-zero temps it's best to place cardboard behind the grill, in front the radiator (but NOT covering, choking, the radiator), yet still provide airflow to it. Cold air at high travel will cause stuff like this to occur.
 

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To me, it seems unlikely that ice could form in the intake manifold. Even with the stock airbox getting the cold air and it being that cold out, your air intake temps at the manifold will still be about 100 deg F. Even the air under the hood has to be pretty warm at the least.

Anyways, glad it corrected itself! Always gotta be a little more careful in extreme weather.
 

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Even with the stock airbox getting the cold air and it being that cold out, your air intake temps at the manifold will still be about 100 deg F.
No. That's wrong. Its not that hot. If anything, its a few degrees warmer. Convection doesn't occur that fast, plus the intake manifold is generally very cold when cruising around. If you idle for a while, it'll get hot but will still cool down when driving.

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Very odd; I know that small airplanes have a "carb heat" function specifically to prevent this issue on airplanes, but I've never heard of it happening on a car.
True. On our planes we use it greatly, even at temperatures close to 10F. The amount of cold air coming in really hurts the performance. What the OP is pretty much spot on as to what would happen with ice on our planes, the engine would give no heads up or similar, but you start feeling the decline in performance after a while eventually leading to the engine dying, until the ice is melted. On planes with Turbo you can hear a little bit more of the turbo whine when the temperatures are affecting the performance of the engine.

The fact the car stopped and the engine was hot, probably helped in the car restarting, as the heat was not fighting against cold temperatures in motion, and therefore melting the ice.
 

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No. That's wrong. Its not that hot. If anything, its a few degrees warmer. Convection doesn't occur that fast, plus the intake manifold is generally very cold when cruising around. If you idle for a while, it'll get hot but will still cool down when driving.
I can only speak to my ait which was around what I said (100g) when cruising down the highway in -11 deg weather
 
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