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I have only had my new TDI for a little over a month. Of course, at this time of year, the average weather is getting colder. My mileage is going down steadily. I started out the first tank at 46, then 45, then 42, and this one I am currently working on looks like it is going to hit around 40 or 41. Is or can this be related to the decrease in average temp? This week, it has been in the mid 30s during the day.

If not this, anyone got any suggestions?

Thanks,

Frog.
 

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It seems to a common thing over here in the UK. Supposedly the oil companies alter the fuel for the colder conditions to prevent it gelling up etc. I don't know about where you are though. Also I would think the car is on cold running because it takes longer to get up to temprature but I don't know for sure.
 

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Yep, comes with diesel territory unfortunately. I remember getting just shy of 50mpg consistently per tank. Now I'm averaging low 40s.
 

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Yes.

Engines run richer to maintain their temperature. Think of it as, the choke remains on longer. Another side effect is that pollution is actually worse in some areas during winter because all the cars have increased emissions.

I lost about 5% off my mileage during this Georgia cold snap (we don't normally get below freezing this hard or often till Feb if then)
 

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Engines run richer to maintain their temperature. Think of it as, the choke remains on longer.
I think your getting confused with petrol Chris. Diesel engines don't have a rich or weak mixtures or chokes what ever fuel is injected is supposed to burn as it has a full charge of air each time, even more with a turbo.

Yes you will find the fuel con drop a bit over these colder winter months. Mine has dropped from 43mpg to 41mpg which isn't much I know. They also take a longer time to warm up to normal operating temperature. In summer my 4.5 mile trip to work the gauge would rise to normal after 3 miles. Now today it only reaches half way between. You only have to watch your MFI/MFD in summer mine shows 40+ mpg now its only showing 30 mpg.

I've thought of making a shield for the radiator to reduce the flow over the engine but chitty says they aren't needed. ;)
 

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I've thought of making a shield for the radiator to reduce the flow over the engine but chitty says they aren't needed. ;)
Uh oh...some quoted me, I have to be careful what I type.:panic:

Not needed but helpful depending on how cold it is. I wouldn't do it unless you live in a really cold area or commute during the early morning.
 

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:nana2:

Is Mileage temperature related?

I was going to comment last night but I got involved in my reply I forgot.

It seems a strange title I think it should have been Is fuel consumption temperature related? as we've found it is. ;)
 

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Cold air is also thicker than than warm air thus causing more aerodynamic drag and cause the car to use more fuel The engine will make more power though.

My best fuel milage and top speeds (59 mpg and 152 mph not at same time lol) comes in warm temps of 25 degrees and above.
 

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"I think your getting confused with petrol Chris. Diesel engines don't have a rich or weak mixtures or chokes what ever fuel is injected is supposed to burn as it has a full charge of air each time, even more with a turbo."

Don't they slightly advance the timing and increase the fuel when they're cold or is that just on older engines Keith?
 

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Don't they slightly advance the timing and increase the fuel when they're cold or is that just on older engines Keith?
Which are you talking about petrol or diesel? ;)
 

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Diesel cold start devices

Well different manufacturers have different methods with cold start devices. On the old inline fuel injection pump when you pulled the cold start knob in the cab it just increased the rack length in the pump so more fuel was injected. Some use a fast idle device which is a wax element like a thermostat thats coupled into the cooling system. As the coolant warms up the the fast idle backs off so you have normal idle speed. Some have a Cold Start Injector is located in the inlet manifold. This is used to supply extra diesel fuel to the engine when cold to create a richer mixture to assist in starting.

As for advancing the injection timing on an inline pump there are mechanical bob weights that fly out with speed and that advances the pump shaft speed so it injects earlier. The distributor type pump the cam ring advances with engine speed and therefore juel is injected earlier.

A lot use glow plugs as you know to aid cold starting to increase the cylinder temperature before the fuel is injected. Some have an heating element with a timer in the inlet manifold to increase the temperture of the air inducted.

Diesel fuel will burn/ignite in a temperature of 400 deg C therefore the temperature when the engine has warmed up has to be 600 deg C to ensure ignition takes place. ;)
 

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During the latest cold snap here in Wisconsin, my MPG has dropped from over 38 to 32 (mostly city driving) in my '10 Jetta w/dsg. And yes, I've noticed the engine takes much longer to reach normal operating temperature.
 

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I have a Golf tdi, 2.0, manual, 17,000 miles.
This is my first post to the forum, I live on Long Island, New York

I was getting ~48 on my 35 mile highway commute during the summer (average temp 85F)
Now I'm down to ~41 (average temp 35F)
Temp this morning was in the low 20'sF, I only acheieved ~36mpg going to work :/
 

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I've lot 5-7 mpg since it got cold here in FL. on trips to the airport i usually get 48mpg, been getting 39-42. Even upped the air in the tires back up to 38PSI. It warmed up a bit this afternoon, 74F and my trip back from the airport, got 45, so a little better. Definitely temperature sensitive.
 

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Weather related mileage

I drove to St Louis from New Orleans in my 2011 Golf TDI and watched my mpg slowly decrease as the temp lowered going north.
On the return trip to New Orleans I watched my MPG increase as the outside air temp increased.

Did not know if that was normal until I read this thread.
 
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