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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old May 14th, 2019, 07:34   #31
tikal
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Originally Posted by sloinker View Post
I can get over 60mpg in the summer going to work. I'ts a chore and 55-60 mph tends to anger folks on the 80mph freeway. The 51psi tires are a little harsh and the speed to merge is counted in minutes. If I run my aircon, drive normally at the 80mph limit, merge quickly, run my tires at 40psi I will get consistent mid 40's in the summer depending on wind and temperature. In the winter with cold temps, winterized diesel and snow tires I can consistently get upper 30's to low 40's. This is actually true for both my hatchback and sportwagen, both dsg's. My unfixed manual 2015 Passat managed a couple miles more per gallon but she is history with the buyback.
Good summary! I would venture to say this assessment is spot on for the majority of CR TDIs on the North American roads.
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Old May 19th, 2019, 18:40   #32
Webbie1
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After driving how I normally drove for a day, and getting a piddly 39 mpg actual mileage, I went back to trying to drive for mileage. It turns my 50 minute drive into an hour drive, but it's worth it. With 470 miles on this tank, I show an indicated 57mpg average. I know actual mileage will be less, but still over 50 mpg. On top of that, I checked my tire pressure today and found they were all inflated to 35 psi. I filled them to 45 psi to see how much that improves mileage (51 psi is max on the stock Hankook tires). I'll get some idea tomorrow. I only drive 3 times this week, as it's my carpooling friend's turn to drive on Tuesday and Thursday, and I think I'll take the motorcycle on Wednesday, so I'll have about 700 miles on this tank when I fill it. Hopefully 14 gallons or less.

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Old May 21st, 2019, 07:09   #33
scooperhsd
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It depends on your motorcycle `- my TDI's do better MPG than my bike (1998 Honda Valkyrie)
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Old May 21st, 2019, 09:15   #34
Webbie1
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Originally Posted by scooperhsd View Post
It depends on your motorcycle `- my TDI's do better MPG than my bike (1998 Honda Valkyrie)
Oh completely. My TDI does better than the bike too. I'll get about 40mpg on the bike......but it won't be at 65-70 mph.

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Old May 22nd, 2019, 12:26   #35
andreigbs
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Quote:
... I filled them to 45 psi ...
Yikes, that's a bit much no? I know the tires may be able to take it just fine, but even at my current 35psi it feels a little harsh.

You're also likely to chew up the insides of the tires being overinflated. Saving money on fuel to spend on tires still ends up costing you.

To each his own I guess.
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Old May 22nd, 2019, 12:28   #36
Webbie1
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Originally Posted by andreigbs View Post
Yikes, that's a bit much no? I know the tires may be able to take it just fine, but even at my current 35psi it feels a little harsh.

You're also likely to chew up the insides of the tires being overinflated. Saving money on fuel to spend on tires still ends up costing you.

To each his own I guess.
If max inflation is 51 psi, then 45 psi is not "overinflated". It doesn't feel the least bit harsh.

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Old May 23rd, 2019, 07:07   #37
andreigbs
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Debatable; some would say VW has determined the "correct" tire pressure, which is found on the driver's door post or in your manual or sometimes on the fuel filler door. Inflating beyond that value would be considered "overinflated."

Glad it doesn't feel harsh though, maybe just keep an eye on the wear of the middle section of the tires.
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2014 Golf TDI // 45xxx miles // 38 MPG - buyback'ed
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Old May 23rd, 2019, 07:16   #38
Webbie1
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Quote:
Originally Posted by andreigbs View Post
Debatable; some would say VW has determined the "correct" tire pressure, which is found on the driver's door post or in your manual or sometimes on the fuel filler door. Inflating beyond that value would be considered "overinflated."

Glad it doesn't feel harsh though, maybe just keep an eye on the wear of the middle section of the tires.
You mean like Ford did with the Explorers that were rolling over on everyone? Yeah...they have inflation values that provided the type of ride they wanted to sell the consumer. The tire manufacturers always know what's best for the tires they make. I'd go with the tire manufacturer EVERY time when there's a discrepancy.

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Old May 23rd, 2019, 08:50   #39
IndigoBlueWagon
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Tire manufacturers generally don't offer a recommended inflation pressure, just a maximum.
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Old May 23rd, 2019, 08:55   #40
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Originally Posted by IndigoBlueWagon View Post
Tire manufacturers generally don't offer a recommended inflation pressure, just a maximum.
That's a fair point. The point that I was really trying to make is, at 45psi, my tires that are listed at 51psi max are not over inflated. (and the Ford reference is definitely relevant, because they were recommending an inflation level that was based on soft ride only, with no concern for the beads breaking loose from the rim because the tires were under inflated)

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Old May 23rd, 2019, 09:16   #41
IndigoBlueWagon
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This is a topic people can argue about endlessly because there are no absolutely right answers. But I do have a few observations.

First, it's probably a mistake to generalize from Ford's error with the Explorer that all auto manufacturers suggest tire pressures that are dangerously low. I doubt that's true. (And as an aside, I think the issue with the Explorer was that the low tires caused the truck to skid and roll over. Tires didn't, as best I can remember, come off the rims).

Second, data I've seen show the Passat's recommended tire pressures at 35F/35R. The Passat isn't a very heavy car for its tire size, so I'm betting those pressures are more than adequately safe.

Third, higher tire pressures can compromise handling and braking. Running pressures that are too high is a classic mistake for drivers that are new to race driving. Almost everyone at a track has to lower tire pressures as the tires warm up to maintain steering and braking grip.

Finally, I've noticed that VW's recommended tire pressures have increased over the years. I don't know if that's because they feel it's safer to run higher pressures, or if they're assuming that most drivers won't bother to check tires and they want to have a buffer to be sure they're minimally inflated.
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Old May 23rd, 2019, 09:41   #42
Webbie1
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Quote:
Originally Posted by IndigoBlueWagon View Post
This is a topic people can argue about endlessly because there are no absolutely right answers. But I do have a few observations.

First, it's probably a mistake to generalize from Ford's error with the Explorer that all auto manufacturers suggest tire pressures that are dangerously low. I doubt that's true. (And as an aside, I think the issue with the Explorer was that the low tires caused the truck to skid and roll over. Tires didn't, as best I can remember, come off the rims).

Second, data I've seen show the Passat's recommended tire pressures at 35F/35R. The Passat isn't a very heavy car for its tire size, so I'm betting those pressures are more than adequately safe.

Third, higher tire pressures can compromise handling and braking. Running pressures that are too high is a classic mistake for drivers that are new to race driving. Almost everyone at a track has to lower tire pressures as the tires warm up to maintain steering and braking grip.

Finally, I've noticed that VW's recommended tire pressures have increased over the years. I don't know if that's because they feel it's safer to run higher pressures, or if they're assuming that most drivers won't bother to check tires and they want to have a buffer to be sure they're minimally inflated.
Agree with you on everything you said. I'm certainly not implying that all manufacturers are intentionally recommending lower tire pressures which are dangerous, for the sake or ride quality. But know that this has happened is what leads me to believe the tire manufacturer more the the auto manufacturer who is slapping the tires on their cars. And Firestone took full responsibility for the tire failures (which it appears were caused by excessive heat, at least part of which was caused by Ford's 26psi inflation recommendation).

I also agree that more fully inflated tires may suffer traction issues before one that's softer. For my extended highway cruising, that's less of a concern for me (at least in Spring - Fall months) and it's worth it to gain 2-3 mpg by having them at 45 vs 35. We'll see how it works out next tank of gas....I inflated them up about halfway through this tank, so the numbers are not completely reliable yet. Time and experimentation will tell. Some guys going for top fuel efficiency run them right up to 51psi. I didn't want to go that extreme, so I settled at 45psi for now.

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Old May 23rd, 2019, 11:10   #43
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After doing some research, I could be wrong about this approach.....I may bump the pressure down a bit. In fact, it may be more like 40 as-is, because the gauge on my inflation tool tends to read a little high when compared to a real tire gauge. But 45 may be higher than where I'd want to be. I'm going to check the actual inflation with a real gauge, and adjust it down to at least 40psi if it's more than that cold.

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Old June 6th, 2019, 05:53   #44
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38.6 all around driving on flat ground with conservative pedal action jsw (12)
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Old June 9th, 2019, 13:50   #45
johnsTDI
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The Key to getting the best possible fuel economy is for 1 having a good Clean fuel System to start & yes having a fairly clean Air filter follows afterword since Diesel engines suck alot of Air into the engine. You will see the best results in MPG's if the fuel system is clean. i use shell V-Power Diesel in my TDI No need to keep using this fuel i have used 2 tankfulls 3rd one yesterday filled on V-Power Just to make sure Fuel system is absolutley clean! and then i will switch back to there regular shell Diesel. i bought my 2012 VW TDI used so im not sure on what cheapo mystery diesel fuel other person used. lol So far the fuel mileage keeps climbing and climbing.
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