At what temperature is TDI intercooler not needed?

This seems to come up a bit on the VW TDI forums when discussing winter radiator blocking. One group says to cover everything but leave the opening that feeds the intercooler open and the other group says they cover all openings in the winter and haven't had any issues. Obviously, there's a point where the intake air is cold enough that an intercooler isn't really needed but where is that point? Living in an area where -40C is not uncommon and -15C to -30C is the regular temperature range over the winter I wonder if blocking off the intercooler opening isn't a good idea, at least for the coldest few months.
 
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My old Powerstroke doesn't even have an intercooler and has pulled 20k lb net payloads in 90 degree heat and still runs strong at 315k miles. I would say not to think about it too hard. Having said that I don't understand the purpose of covering the intercooler. Its not like the air can be too cold entering the engine.
 

Astro14

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Originally Posted By: SVTCobra
Its not like the air can be too cold entering the engine.
It sure as heck can be too cold...where that temperature lies depends on vehicle design, but somewhere between -20 and -40 and the engine simply won't warm up...you get condensation that builds in the oil because it runs cold, interior heat doesn't work, cylinder walls are washed down with extra fuel as the engine runs in open loop and is perpetually in warm-up mode...
 
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And Jetta TDIs inject exhaust gas into the air stream before the main part of the IC, causing moisture to condense in the IC!! Covering the IC keeps the air hotter and minimizes this.
 
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I'd cover it. At the point that Celsius and Fahrenheit are equal, that's darned cold! My car sure would be closing its active vents at that point.
 

Surestick

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Originally Posted By: Astro14
Originally Posted By: SVTCobra
Its not like the air can be too cold entering the engine.
It sure as heck can be too cold...where that temperature lies depends on vehicle design, but somewhere between -20 and -40 and the engine simply won't warm up...you get condensation that builds in the oil because it runs cold, interior heat doesn't work, cylinder walls are washed down with extra fuel as the engine runs in open loop and is perpetually in warm-up mode...
My thoughts exactly. It's a diesel so I don't think there's open or closed loop operation as it's never stoichiometric but it does depend upon the heat of compression to ignite the fuel. At some point the air coming in must be cold enough to have an effect on combustion. Also, the TDIs tend to have problems producing heat in the winter. Intake air at -40 is probably sucking a lot of heat out of the engine. It looks like stock boost goes up to about ~21 psi... I'm not sure what that means in terms of temperature rise. My guess is the limiting factor is the EGT that the exhaust valves see. If the intake temp gets too high the EGT is going to climb and the exhaust valves will end up burning.
 
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I doubt that air temperatures dropping from even 100 to -40 is going to have that much change in combustion temperatures when diesel engines can have over 3000 degree combustion temps and over 1000 degrees of heat coming out of the exhaust manifold past the turbo. If I drove the car from my garage to the end of the driveway to check the mail we might have a problem but if the car gets up to operating temps then I don't see an issue.
 
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Originally Posted By: Surestick
It looks like stock boost goes up to about ~21 psi... I'm not sure what that means in terms of temperature rise. My guess is the limiting factor is the EGT that the exhaust valves see. If the intake temp gets too high the EGT is going to climb and the exhaust valves will end up burning.
Burning valves or melting pistons. But you need to be making some serious horsepower before this really becomes a problem. Like I said my old Powerstroke has a non-intercooled turbo engine and has pulled many a load in 90 degree heat on a stock engine and is my daily driver with 315k miles. I don't think intercooled diesel engines built for fuel economy running in -20C weather is going to pose a problem if the intercooler is covered or uncovered.
 
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I must have missed those discussions. My climate is warmer but we see plenty of cold, and I've never blocked off anything on my cars. I might this year though, just to get it to warm up faster. No plans to block off the IC though, I do lots of highway miles and I suspect any condensation won't last long. I only want the thing to warm up faster, at 0F it can take 10 miles to make the temp guage move! That's not to make heat, that's just to make the needle move slightly! It's a 50 or 55mph zone too.
 
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Originally Posted By: Surestick
Originally Posted By: Astro14
Originally Posted By: SVTCobra
Its not like the air can be too cold entering the engine.
It sure as heck can be too cold...where that temperature lies depends on vehicle design, but somewhere between -20 and -40 and the engine simply won't warm up...you get condensation that builds in the oil because it runs cold, interior heat doesn't work, cylinder walls are washed down with extra fuel as the engine runs in open loop and is perpetually in warm-up mode...
My thoughts exactly. It's a diesel so I don't think there's open or closed loop operation as it's never stoichiometric but it does depend upon the heat of compression to ignite the fuel. At some point the air coming in must be cold enough to have an effect on combustion. Also, the TDIs tend to have problems producing heat in the winter. Intake air at -40 is probably sucking a lot of heat out of the engine. It looks like stock boost goes up to about ~21 psi... I'm not sure what that means in terms of temperature rise. My guess is the limiting factor is the EGT that the exhaust valves see. If the intake temp gets too high the EGT is going to climb and the exhaust valves will end up burning.
Assuming your maximum boost pressure is 21psi on a 68F day, the temperature out of the compressor would be about 290F. Assuming the air-air intercooler is 88% effective, the intake manifold temperature would be 95F. Now cool the ambient temperature down to -40F. With the same 21 psi boost, compressor out temperature would be 137F. If the intercooler is not blocked off, the intake manifold temperature would be -19F. I don't know how effective the intercooler would be if it was blocked, but I doubt it would be 0% effective. Making a wild guess of 20% for the effectiveness of a blocked-off intercooler would yield an intake manifold temperature of 102F, which is close to the 95F that the engine sees on a warm day. Now heat up the day to a worst-case temperature of 110F. 21 psi boost would yield a compressor out temperature of 350F. And an 88% effective intercooler would give an intake manifold temperature of 139F, which is close to what the compressor out temperature would be on a -40F day. I think you can block off the intercooler.
 
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