'05 Golf TDI sudden low fuel economy

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golfKart

New member
Joined
Jul 25, 2010
Location
Raleigh, NC
TDI
VW Golf
I've just discovered this forum in trying to diagnose the low fuel economy I've just begun to observe in my golf so please excuse me if I've missed an older post that might help. I did try to search first!

2005 Golf TDI 4-door automatic transmission 105,000 miles
Fuel economy generally around 38mpg, mostly highway driving -- daily roundtrip ~ 40miles

I've already changed fuel & air filters but am still having mileage around 33/34mpg. Any ideas as to what else might be the culprit. The power seems to be reduced as well from what I'm used to but I'm less certain about that. Thanks for your thoughts!
 
impalaman

impalaman

Member
Joined
Dec 22, 2008
Location
AL
TDI
2005 Golf GLS TDI
golfKart, I also have an 05 Golf 4-door TDI. Mine has 115,000 miles and I am experiencing the exact same symptoms as you.

However, I do know that my main cooling fan is currently not working. The smaller fan for the A/C is working however. I've been meaning to change out the big fan, but haven't had the time.

I'm wondering whether or not a malfunctioning main cooling fan could reduce mpg. Check your fan. With the ignition switch on, but engin not cranked .... turn on the A/C and keep the fan knob in the low number one setting. The main fan should be turning at a low speed. If not, it's bad.
 
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rubadub

Active member
Joined
Jul 20, 2010
Location
South Carolina
TDI
2002 Jetta TDI
ok, this sounds A LOT like a vacuum leak. Check your vacuum lines especially the hard plastic one coming off the right side of the engine. It is a hard plastic tube about 4-5 inches in length with a 90 degree bend. Mine had split causing some major power loss and my brakes weren't working as well. Just find this hose and feel it to determine its integrity.
 
Paradoxjr

Paradoxjr

Member
Joined
Jul 2, 2010
Location
Fort McMurray, Alberta
TDI
2011 Jetta TDI - Highline
A vacuum leak would cause brake issues??

I have only been getting about 35mpg lately and my brakes have been horrible.. I couldn't lock the tires up if i tried right now...
 
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rubadub

Active member
Joined
Jul 20, 2010
Location
South Carolina
TDI
2002 Jetta TDI
Paradox, yes the power brake will not work without vacuum leak. there is one hose in particular that there are a lot of problems with cracking. If you look at the right side of the engine there is a hose coming out of a cylinder that goes back with a ninety degree bend that goes into a pancake shaped cylinder. This cylinder is the brake booster and that hose is a vacuum line. You can feel the hose around the connection for cracks but mine was completely split. I would not be surprised if this was your problem. i can include a picture if you need help locating it but I just went to advance and bought some new hose and now it works better than ever
 
jettawreck

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
rubadub said:
Paradox, yes the power brake will not work without vacuum leak. there is one hose in particular that there are a lot of problems with cracking. If you look at the right side of the engine there is a hose coming out of a cylinder that goes back with a ninety degree bend that goes into a pancake shaped cylinder. This cylinder is the brake booster and that hose is a vacuum line. You can feel the hose around the connection for cracks but mine was completely split. I would not be surprised if this was your problem. i can include a picture if you need help locating it but I just went to advance and bought some new hose and now it works better than ever
Click to expand...

Power assisted brakes work on vacuum, so the power assist will not work WITH a vacuum leak.
Neither will your turbo function properly as the actuator works via a vacuum diaphram.
Check/test your MAF sensor. If its faulty (common, especially on the older ALH's) its the first suspect in low power/sudden loss of mpg issues. Some just lose power and no loss of mpg, some do. Go figure.
 
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rubadub

Active member
Joined
Jul 20, 2010
Location
South Carolina
TDI
2002 Jetta TDI
jettawreck said:
Power assisted brakes work on vacuum, so the power assist will not work WITH a vacuum leak.
Neither will your turbo function properly as the actuator works via a vacuum diaphram.
Check/test your MAF sensor. If its faulty (common, especially on the older ALH's) its the first suspect in low power/sudden loss of mpg issues. Some just lose power and no loss of mpg, some do. Go figure.
Click to expand...
Haha sorry I mis spoke. Sorry that sentence there was probably not correct either. But I assume the problem is a vacuum leak because he is experiencing power loss and loss of braking power
 
jettawreck

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
rubadub said:
Haha sorry I mis spoke. Sorry that sentence there was probably not correct either. But I assume the problem is a vacuum leak because he is experiencing power loss and loss of braking power
Click to expand...
That's OK. Kind of hard to keep track who's commenting on who's issue.
Paradox has/had brake issues, I guess. The OP didn't mention it. The thread got kind of mixed w/issues. :confused:
 
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