MPG at 75mph

duwem

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Forgive me, I'm new, but I'm hoping this is a simple question.

I see guys claming 50mpg on TDI cars.

I assume that is 55-65mph?

Does driving at 75mph significantly drop these numbers.

I would be happy with 40-45mpg in a Golf MK4, but wondering what speed gives what mpg.

Thanks
 

IndigoBlueWagon

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My fuelly average is 45 MPG for the past 52K in my '02 wagon, probably mixed 50/50 city highway. 75 is my default speed on the highway. In favorable weather (summer fuel, cool enough to not need A/C), I've seen just shy of 50 MPG (49.6) on a trip at that speed. On most trips I see 45-47 MPG, but I'll also go faster than 80 if traffic is moving faster. I recently got 46 on a drive from Richmond to MA, and I averaged over 70 MPH for that trip including stops.

I know people do better than I when they drive slower, but I'm not willing to spend more time in the car to get a few more MPG.
 

tbone1989

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I do about 70-80 and average 38-45. Depends on which way I'm going to work. I would like to just do 70 but on the parkway here in nj, if your not going fast enough, you will get run over.
 

ruking

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Welcome to the forum. Actually your questions can be extremely simple. Mostly, one is dealing with VARIANCE, so it can be extremely (more normally) complex. In that sense, normally one is concerned with what one is ready, willing and able to get.

Once you know the parameters of the 1.9 TDI engine, you can operated it in ways to get literally whatever mileages (RANGE) you want, given your conditions. My ranges have been from 44 to 62 mpg (175,000 miles) . There are loads of folks who really don't even know what the specifications ARE, let alone understand how to use them to get maximum fuel mileages or whatever. Whether you want to operate in those manners are different questions and can be in perpetual flux.

So yes to answer your question, 50 mpg in a MK IV Golf TDI 5 speed manual is do able.

No, I can get 50 mpg (range of 48-52) in a daily 54 miles R/T commute taking anywhere from 45 min to 1.5 hour for a 27 miles leg, for 11 actual commute days (average). I can also get 50 mpg @ 90 mph, on a road trip. I have routinely gone 75 mph on the highway (road trips) and posted 59 mpg. I have yet to do a longer time perpetual operations at 55 to 65 mph, but I swag it would be more along the lines of 60 to 65 mpg. Again this is on a heavier car than your Golf TDI Mk IV.

So for a snap shot, I filled yesterday after 3 weeks and not even caring about mpg, app 500 miles 10 gals for 49.7 mpg. Pretty easy to do around here, especially if you keep it under 95 mph. :)
 
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oilhammer

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There are just too many to list....
Yep, I do it every tank. Pretty easily, too.

But keep in mind, if that is the only reason you are looking to buy, you'll be disappointed.
 

Masonjar

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For my 2001 Golf with manual transmission, I've regularly experienced 1000+km on <50l of fuel (<5l per 100km or 47+mpg) when driving 120km/h (75mph) for long stretches.

Andrew
 

MikeMars

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...
Does driving at 75mph significantly drop these numbers.
...

The forum's rule of thumb used to be '120 - speed = instantaneous MPG' on the highway, i.e., at 60mph you get 60mpg, at 75mph you would get 45mpg (on the flat, no wind, moderate temperatures, no A/C or heater, & engine already up to full temp).

I don't know if this rule applies to the Mk4. But it should at least give you an idea of the effect of speed on fuel consumption.
 

duwem

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Thanks guys.

Ruking, your numbers seem higher than average I have seen. Have you modified your car? I would think steady state flat highway, no wind same engine and trans and aprox same vehicle weight most stock cars would get about the same MPG.

I see how acceleration would play into it and how mods would change that.
 

TheHolyCobra

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Driving 75 mph ACTUAL (about 79-80 on the speedometer) I can get over 50 mpg.

In the summer in 80* heat, with a stuck thermostat and slipping clutch, I got 57.1 mpg hand calculated on a tank of about ~300 miles. Full tank of gas, no wide open throttle or AC during the trip, traveling at an actual 75 mph. Probably would have gotten over 60 mpg but there was actually about 5 miles of city driving and a shut down in there.

Car is modded with a tune (RC3), full 2.5" turboback exhaust with no cat or muffler, and tires were at about 45 psi. 235,000 miles on the car as well.
 

ruking

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The cars are bone stock, as my TDI's block states. NorCA and many western states are NOT FLAT. 50 mpg was once clocked in a driving rain going from sea level up passed 4,200 ft and fuel at or around sea level. I do not use CC as it does not allow as much flexibility as driving it under foot.
 

hotpocketdeath

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The general rule of thumb is 7% lose in fuel economy for every 5mph increase in speed.

While 7% is the widely accepted rate of lose, the point where it starts has differences. Some say every 5mph over 60mph, while some sources say 5mph over 65mph.

This is information from sources such as the Department of Energy.
 

tditom

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... I can also get 50 mpg @ 90 mph, on a road trip. I have routinely gone 75 mph on the highway (road trips) and posted 59 mpg. ...
This is absolute BS, unless you spent much of that time driving down a mountain.
 

tditom

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The forum's rule of thumb used to be '120 - speed = instantaneous MPG' on the highway, i.e., at 60mph you get 60mpg, at 75mph you would get 45mpg (on the flat, no wind, moderate temperatures, no A/C or heater, & engine already up to full temp).

I don't know if this rule applies to the Mk4. But it should at least give you an idea of the effect of speed on fuel consumption.
This is pretty accurate for most MkIV's
 

ruking

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This is absolute BS, unless you spent much of that time driving down a mountain.
Since we do drive up mountains, going back down is usually involved in getting back. Even you know the legs should average out.

Well for sure YOU have documented that you can't do it !! :eek: So are we to assume your highs of 54/52 mpg are also BS? So I can see why you think it BS.

Do I get 59 mpg @ 75 mph highway all the time? Absolutely not !! I am just fine with mpg like the last fill @ 49.7 mpg. Coincidently 49.7 mpg is not too much different than what you have documented.
 
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tditom

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So the new guy asks what speed yields 50 mpg, and you say you can get it at 90mph :rolleyes:
Why not take the opportunity posed by his followup question to clarify that you calculated 50 mpg at 90 mph going downhill over a short period of time if that is true? Why answer his original question with some special, rare case that was not clocked over a full tank?

I call BS on anyone claiming 50 mpg @ 75 mph (unless they've modified their final drive ratio)
 

MikeMars

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...
I call BS on anyone claiming 50 mpg @ 75 mph (unless they've modified their final drive ratio)
Easy... as long as you use imperial gallons :)
 

ruking

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Good point, maybe ruking was using that unit of measure. :)
Even you know that is not true. 128 oz in a gal, if that is/was ever unclear, in any way.:p
 
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listerone

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Since we do drive up mountains, going back down is usually involved in getting back. Even you know the legs should average out.
I've often wondered about that.The only "hills" I've ever driven in my diesels are the hills of New Hampshire/Vermont and East Tennessee on I-75,and on none of those occasions was I paying real attention to mileage.And I'm sure that those hills don't come close to equalling the mountains that one encounters out West.But on a given "mountain",everything else being equal,does the fuel you save going *down* really equal out the extra fuel you use going *up*.If I was a trained physicist...or had any experience with real mountains...I suppose I'd know the answer.:D
 

ruking

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I've often wondered about that.The only "hills" I've ever driven in my diesels are the hills of New Hampshire/Vermont and East Tennessee on I-75,and on none of those occasions was I paying real attention to mileage.And I'm sure that those hills don't come close to equalling the mountains that one encounters out West.But on a given "mountain",everything else being equal,does the fuel you save going *down* really equal out the extra fuel you use going *up*.If I was a trained physicist...or had any experience with real mountains...I suppose I'd know the answer.:D
I think it is more about what you are used to and you factor it in. If you are not used to it, you don't factor it in. Why would you?

So for example, to get to more local ski resorts, we go from sea level to app 7,200 ft. http://www.waymarking.com/waymarks/WM40HN_Donner_Summit_I80_California
 
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ruking

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So the new guy asks what speed yields 50 mpg, and you say you can get it at 90mph :rolleyes:
Why not take the opportunity posed by his followup question to clarify that you calculated 50 mpg at 90 mph going downhill over a short period of time if that is true? Why answer his original question with some special, rare case that was not clocked over a full tank?

I call BS on anyone claiming 50 mpg @ 75 mph (unless they've modified their final drive ratio)
Funny how you don't post YOUR experiences under similar conditions.

Or do you just like to whine in print? Is it that time of the month, Tom?

By the waythat example was a 10+ gal fill. The situations change, but this kind of stuff (50 mpg) is done multiple times and under multiple conditions and fuller tanks rather than the silliness you suggest . So like I say, 50 mpg is just another day.
 
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tditom

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Funny how you don't post YOUR experiences under similar conditions...
The mpg's I calculate are in my info under my user name on each post. These were taken over full tanks (at least 14 gal fills) over many years- not after coasting down a mountain and filling up again :rolleyes:. Why would I obfuscate the issue by throwing out some anomalous reading?

As I posted earlier- my experience fits the "120 rule", where mph+mpUSg=120. This is most likely much more helpful to the OP than your nonsense...
 

ruking

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The mpg's I calculate are in my info under my user name on each post. These were taken over full tanks (at least 14 gal fills) over many years- not after coasting down a mountain and filling up again :rolleyes:. Why would I obfuscate the issue by throwing out some anomalous reading?

As I posted earlier- my experience fits the "120 rule", where mph+mpUSg=120. This is most likely much more helpful to the OP than your nonsense...
Yes you confirm what I already have said, you don't know how to get 50 mpg at 75 mph. Indeed if I started to get 45 mpg consistently, I'd look to see if something was wrong.

So yes, if I wanted to get 45 mpg @ 75 mph. I'd sure asked you ! Have a good day.
 
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richfunk

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Funny how you don't post YOUR experiences under similar conditions.

Or do you just like to whine in print? Is it that time of the month, Tom?

By the waythat example was a 10+ gal fill. The situations change, but this kind of stuff (50 mpg) is done multiple times and under multiple conditions and fuller tanks rather than the silliness you suggest . So like I say, 50 mpg is just another day.
What tditom is saying is that your post was misleading! No need to bicker, just don't mislead potential buyers by saying you car gets 60+ going 90. Then never tell them that its only when coasting down a hill in neutral. You talking like that leads me to believe your a salesman at a stealership. :confused:

In reply to your post above mine. If you have info share it if not just read on here like everyone else. When did we go back to grade school?
 
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ruking

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What tditom is saying is that your post was misleading! No need to bicker, just don't mislead potential buyers by saying you car gets 60+ going 90. Then never tell them that its only when coasting down a hill in neutral. You talking like that leads me to believe your a salesman at a stealership. :confused:

In reply to your post above mine. If you have info share it if not just read on here like everyone else. When did we go back to grade school?
You might want to ask TDI TOM that question, as you are asking the wrong guy. But you knew that.
 
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richfunk

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So the new guy asks what speed yields 50 mpg, and you say you can get it at 90mph :rolleyes:
Why not take the opportunity posed by his followup question to clarify that you calculated 50 mpg at 90 mph going downhill over a short period of time if that is true? Why answer his original question with some special, rare case that was not clocked over a full tank?

I call BS on anyone claiming 50 mpg @ 75 mph (unless they've modified their final drive ratio)
You might want to ask TDI TOM that question.
Case and point... I have no further questions your honor... :rolleyes:
 
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Wksg

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For full tanks of mostly highway driving at about 65 mph, I get around 58-64 mpg (.658 5th) depending on weather, etc. Some tanks I drive faster, usually 70-75 mph range on the highway and then I'm in the 52-56 mpg range.

For the last 30K miles, my average has been 55.1 mpg, and I would guess my average highway cruising speed is in the 65-70 mph range.
 

Art van Law

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50.7 mpg traveling (minimal hills) from RI to VA Beach. Already had 200 miles on the tank when we started out, and filled up at 763 miles, hence 563 miles all hwy and the remaining 200 about 75% hwy. Speed was < 67mph, two adults 170#, one child 100#, and a moderate amount of luggage for a 5d trip. Right foot mod, tires at about 40psi, much P&G, no fast starts, etc.

So you can see I drive w/ economy in mind and got 50.7mpg in a car w/ about 225K miles on the engine.
 

Art van Law

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also meant to post that the A/C was off most of the trip, but when we did put it on, I'd estimate there was a 2-3 mpg decrease.

Had we been doing 75 mph, I bet the mpg would have taken a huge dive south.
 

dieselfuel

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I've had numerous tanks of near 53 mpg when driving cross country, averaging around 77 mph, with sprints up to 95 mph when someone's on my a@#. And that has been with winter fuel and Green Diamond snow tires.

df
 
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