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Old 06-08-2017, 02:42 AM   #1 (permalink)
EcoModding Lurker
Join Date: Jan 2009
Location: Melbourne, Australia
Posts: 18

hatch - '05 Volkswagen Golf Mk.V
90 day: 33.42 mpg (US)
Thanks: 11
Thanked 4 Times in 3 Posts
Unhappy Poor fuel economy - The weather, or my repairs?

VW MkV Golf, with a 1.6 BGU engine (VW 8v rocker finger, FI, non turbo).

I recently did some repairs to my EGR and PCV systems. This happened about the same time as my Summer to Winter weather transition, So I'm asking for advice on what might've caused my new efficiency problems.

My highway efficiency has improved - 5.2 vs 6.3 L/100km but my local trips have become much worse.
I Used to get 6.8-7.2 L on one local trip. Hilly, about 10km (6 mi) at 60 kmh (37 mph) Now I'm consistently getting 9.8! (24 mpg)
Even on longer drives this figure doesn't improve much unless I get to 80+kmh roads (50mph)

Now, I'm trying to work out the cause.
A -Temperature: Since the repairs temps have dropped from 20-25C to 8-15C. As far as I know we don't get winter blend changes to gas in Australia, only to diesel near the snowfields.
B -Effects of my repair? Crankcase breather was missing a clip, so could vent under pressure instead of flowing to PCV. EGR Valve was sticking open occasionally, causing idle problems. This also caused intermittent loss of vacuum. Replaced with new about the same time.

Tyre pressures are all identical [manuf. spec], I've had no impacts or repairs that'd affect wheel alignment, there's been no mods to the car. Carried weight is identical, and all compared runs were w/o AC and with windows closed. Car starting from cold, Consumption measured by OE cluster display.

I've got a poorly substantiated suspicion my problems are due to poor efficiency at low load. As mentioned, hwy efficiency is good. Steeper hills at 60kph are matching what I remember but maintaining that speed on level ground seems worse ~6.3 vs ~4.5 previously. I'm hesitant to call that data though, as instantaneous fuel economy depends on when you look at the screen.

- - Old - New
- L/100km MPG L/100km MPG
Highway 6.3 37 5.2 45
Local ~7 33 9.8 24
Temperature 20-25c 68-77f 8-15c 46-60f
Hills, 60kph 10-15 23-15 same -
~4.5 ~52 ~6.3 ~37

So, um, that was a long post. Any pointers? Things to check that I missed?

Is there any way to get my short-trip fuel economy back?

Last edited by ballo; 06-08-2017 at 03:07 AM.. Reason: Added table because, man, that was longer than I thought
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