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Why don't TDI's like winter

50K views 33 replies 25 participants last post by  finalkg 
#1 ·
I have a 2010 Jetta Sportswagen and it barely gets in the 30 range during the winter is there anything i can do to improve the gas mileage for the winter like using a fuel additive
 
#27 · (Edited)
There should be a prominent cold weather sticky. This question comes up so much it'd be nice for peeps to find a one stop shop for information. You know, something with links to Frost Heater, IDParts, foam insulation videos, etc.

I have a 40 mile one way commute so I get to see the full range of warmup and steady max mileage at temp. All cars, diesel or gas, will get lower fuel mileage in the winter. But, of course, diesels are hit harder due to much less waste heat.

Most already know this, but I'll explain it as I know it. A gasoline engine mixes air and fuel, compresses it and then ignites it. The leaner that mix is, the hotter it can be. Think of it like a bunsen burner or a gas stove. Without enough air the flame turns yellow and cold. Add air and it turns blue and hot. A gas engine is no different in this respect and as such is much hotter than a diesel and can weather better.

The diesel, on the other hand, doesn't toss any fuel into the mix until it's ready for combustion. It's more like lighting a lighter in a compressed air space and it's also the reason the fuel pressure is a thousand times higher than gasoline non direct injection engines.

All engines, regardless of fuel, suffer from two major obstacles to overcome. 1. Get heat into the engine. 2. Keep heat in the engine. Manufacturers do things like size the radiator, select thermostat, control cold air intake, etc. but the manufacturer rarely goes the extra mile required to see major improvement in these areas (this is changing in the current marketplace) due to costs and consumer demand.

The biggest recent change (driven by consumer demand) is the active shutter. Cardboard and ty-strap uses have known for years that lower heat loss at the radiator helps keep both the engine and the operator toasty and warm with the lesser known benefit of slightly improved aerodynamics. Now, as active shutters gain popularity, this temperature can be regulated year round. Effectively, this regulates radiator capacity, which is way too high in the winter. A thermostat may be able to regulate flow, but it can't control how cold the water is returning to the engine. You would need a tempering gate to achieve this, or, just keep the water from getting too cold in the first place. Ironically, the active shutter is designed as an aerodynamic tool, but in the winter, has more value throttling cooling capacity in a diesel engine.

I haven't seen active shutters available yet as an aftermarket, so, what am I to do? First, we can get heat into the engine. Some solutions for that are:

Park in a heated garage.
Install a Frost Heater or similar radiator water heater.

Both good starts and allow the engine to heat up quicker by starting at a higher temperature to begin with. The heated garage has other benefits, too, but the cost is hardly justifiable to someone saving fuel costs. Neither are usually available away from home.

Items that keep the heat in are available all the time and include:

Foam covers for the grill.
Pre-made covers for the grill (such as available from IDParts)
Use air recirc in the cabin as much as possible

Grill covers act like active shutters...without the active part. Also, reducing the capacity of your radiator means less cooling is available when the outside temperature goes up. This can be an issue in the Spring when temperatures can swing wildly from day to day. If you are lucky enough to be exposed to the cost cutting practices at VW you may not even have a temp gauge in the cabin to even see you have a problem developing. Some prudence here goes a long way. You may even decide you want a temp reading available. The aftermarket supplies fine solutions.

This is my first year driving a diesel car but is not my entry point for dealing with diesels. I drove this winter with no modifications to see how well VW manages this through engineering and to see what would have the best bang for the buck for me. For me, I have complete confidence that installing a grill cover, as has been done since the first diesel met it's first winter, is a great first step with a Frost Heater being a close second. Cars in more extreme conditions where just starting the car can be a problem will probably prioritize differently and utilize other solutions in addition such as battery blankets, additional batteries, relocated batteries, etc.

Well, there's my viewpoint. Feel free to trash it or correct me as necessary. I'm not perfect. This is just my view into the world. I know I repeated a lot of what others have said, but only because I'm agreeing with you.
 
#29 ·
Buy and install a skid plate so you are able to start a fire under the engine where the oil pan is! Let the fire burn as you watch it. Don't let the flames burn anything. Yeah, this may take some effort and make you colder then a witches tity while watching the flames. But my gramps is always right!
 
#32 · (Edited)
Correct, except the A/C is always on but not under load with the switch off. It is a variable displacement pump that turns but doesn't displace anything when switched off.

With the switch on in cold weather there will not be much if any additional load however, turning on the A/C might make the car defrost quicker.
 
#33 ·
Turn on all that if you like, but the extra load will still only be about 1 horsepower per 450 watts or so (taking efficiency into account). This has potential to help, but should be considered complementary to a more effective scheme like blocking the radiator. In the end, the clear windows and warm tush are of more value to you than the load assist to the engine.
 
#34 ·
2012 TDI here... can relate to the guy on the first page, I get about 32-34 mpg on my 6 mile commute to/from work when its below freezing in chicagoland, sometimes I have to let the car heat up a bit because it does not like throttle when cold. 50 degrees plus I get around 38-42 mpg, but more like 48-51 mpg on the highway. Waiting to see the better numbers after I “unlock” my car from the epa fix.
 
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