WriConsult
Well-known member
OK, I've only had my 2000 Golf TDI for 4 days now, but I'm already noticing an odd thing with the mpg on it. The (indicated) city mpg is spectacular, but the highway mpg is quite a bit lower. I am a fairly decent hypermiler so I am able to get better mpg than your average driver, but even so ... something is out of whack.
Around town I'm pretty consistently able to get mpg in the mid to high 40s (indicated), sometimes low 50s if I'm not having to stop too much. On Saturday I made a 15 mile round trip on suburban parkways and got an indicated 67 mpg.
But on the highway, no such luck. A 25 mile round trip the other day at very moderate (50-60mph) freeway speeds yielded about 43 mpg. Looking at the ScanGauge's instantaneous readouts, I'm seeing 1.1gph to 1.2gph fuel consumption even at a steady 50mph (which equates to substantially less than 50mpg, of course). Consumption rapidly spikes higher than that at higher speeds. And this was after swapping out the original high rolling resistance tires (Bridgestone G009) for my preferred LRR model (Toyo TourEvo) at 44psi.
I understand that a lot of factors are working against me: rainy roads, cool temperatures (30-40F), B50 fuel (4% less energy content), possible ScanGauge calibration error. But if any one of those was the culprit, then my city mpg should be impacted too. But it's not. As you can see above, it's awesome!
One key difference between my city driving and my highway driving is the revs. In city driving I'm almost always shifting between 1700-2000 rpm and only very briefly hitting the rpms I need to steadily cruise the highway. Is there something that could cause efficiency to dramatically drop once the revs get into the 2000 rpm range? ScanGauge shows no codes, by the way.
Things I can think of to investigate:
Later this week I'm going to take some controlled runs at various speeds to see exactly where the mpg drop is happening. I'll do it in both 4th and 5th gear too, to see if there's a sudden drop based on rpm.
Around town I'm pretty consistently able to get mpg in the mid to high 40s (indicated), sometimes low 50s if I'm not having to stop too much. On Saturday I made a 15 mile round trip on suburban parkways and got an indicated 67 mpg.
But on the highway, no such luck. A 25 mile round trip the other day at very moderate (50-60mph) freeway speeds yielded about 43 mpg. Looking at the ScanGauge's instantaneous readouts, I'm seeing 1.1gph to 1.2gph fuel consumption even at a steady 50mph (which equates to substantially less than 50mpg, of course). Consumption rapidly spikes higher than that at higher speeds. And this was after swapping out the original high rolling resistance tires (Bridgestone G009) for my preferred LRR model (Toyo TourEvo) at 44psi.
I understand that a lot of factors are working against me: rainy roads, cool temperatures (30-40F), B50 fuel (4% less energy content), possible ScanGauge calibration error. But if any one of those was the culprit, then my city mpg should be impacted too. But it's not. As you can see above, it's awesome!
One key difference between my city driving and my highway driving is the revs. In city driving I'm almost always shifting between 1700-2000 rpm and only very briefly hitting the rpms I need to steadily cruise the highway. Is there something that could cause efficiency to dramatically drop once the revs get into the 2000 rpm range? ScanGauge shows no codes, by the way.
Things I can think of to investigate:
- Wheel bearings. This week I'll check each wheel to make sure it spins freely.
- Air filter.
- Fuel filter.
- [edit: added] Thermostat. Although the dash temp gauge gets up to 190F reasonably quickly, I've never seen the SG indicate anything higher than 167F. I read the thread about this, and apparently it's common for them not to agree, but in some cases people have found the cause to be a bad 'stat. I'll get that checked out too.
Later this week I'm going to take some controlled runs at various speeds to see exactly where the mpg drop is happening. I'll do it in both 4th and 5th gear too, to see if there's a sudden drop based on rpm.
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