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Old 01-06-2010, 10:04 PM   #1 (permalink)
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Smile Rabbit Diesel '81 does 60.6 MPG

Hello EcoModders,
I've got a 1981 VW Diesel Rabbit I've been trying to get some decent MPG out of for years. I always remembered when they where new hearing people say "Yeah drove to so and so and back and got 55 MPG" but I never could do that well. I live in Tempe AZ, which means the A/C is normally on high and the petal is to the metal, which explains a lot. A couple of months ago the crap they call Diesel these days got to the seals in the injector pump and I had to pull the pump to R&R some seals on the advace mechanism. Put her back in the car and sure enough the distributer head seal leaked like a sieve. Well Virginia, I can tell you for sure you can R&R that seal in the car. Leave two screws in place at a time to keep the parts from flying apart. Along the way I discovered there is conflicting information regarding the timing. From the results I seen I'd say pay no attention to VW factory literature or Haynes which I have always used before, Chilton's call for more advance and the improvement is significant! So I drove up to Globe AZ and back and got 54 MPG, but that is a mountainous trip and coasting is illegal in AZ. Inspired by that result, I switched to Full Synthetic Rotella T 5W40 engine oil. Then I drove to Tucson AZ and back which is pretty flat along with about 10-15% city driving and 3 cold starts - 245 mi. 4.04 Gal for 60.6 MPG. Mostly trying to hold 52-55mph, but drafting a few trucks that were going 60-65. Whoa Who! Pretty annoying in a way, it has me obsessing about what to do next to improve it, when I really need to finish a few little cosmetic repairs and sell it. Its got 80 K on it and would make a great SVO biodiesel WVO project, it already has an auxilliary tank. But I keep think about taking off the vacuum pump, putting on smooth wheel covers, adding a fuel solenoid interrupt switch to get engine braking at zero fuel flow, adding a solenoid to increase idle speed with a/c on so the base idle could be reduced, switching the tansmission oil, etc, etc.

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Old 01-06-2010, 10:07 PM   #2 (permalink)
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that rabbit sounds like a treasure.
i have an '86 accord. welcome.
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Old 01-06-2010, 11:33 PM   #3 (permalink)
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Nice.
Welcome To EcoModder.
I hope yours is as loved as my slightly newer "rabbit" Diesel,
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Old 01-07-2010, 07:19 AM   #4 (permalink)
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I used to own an 81 diesel rabbit. The only way you can drive it is pedal to the metal, especially on hiils. I got about 45 mpg.
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Old 01-07-2010, 10:15 PM   #5 (permalink)
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Make sure the injector opening pressures are up to spec. In the old Mercedes of the same era the injector pressures would gradually drop from 1800 PSI new to under 1500 PSI, which cause it to smoke and run less efficiently, due to poor atomization of the fuel.

regards
Mech
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Old 01-08-2010, 02:11 AM   #6 (permalink)
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Yeah I hear you. Thanks for the suggestion. Most designers of springs never consider fatigue in their design much less creep. Most material suppliers don't even have the data required. Mil Handbook 5 is a great source of this data. I suspected the injectors and replaced them with rebuilds from Parts Place. Unfortunately, their supplier used 1 of four bodies from a different crack point injector and I was about to send them back but I got a Mil surplus injector tester off e-Bay and was able restore it to operating condition and confirm they all had the correct crack point. No improvement so far as I could tell. Its all been in the timing. Too bad it is a challenge to instrument the MPG on this vehicle. I've thought of setting up a % of throttle indicator, so I could tell if drafting was of benefit. That, combined with an EGT gauge, might make optimization within the 2.5 degree range of the cold start advance possible real time.
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Old 01-12-2010, 10:12 PM   #7 (permalink)
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My dad use to own a Diesel Rabbit/Golf in the '80. They run forever. Post some photos so we can enjoy as well.
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Old 01-12-2010, 11:16 PM   #8 (permalink)
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Those were great cars. Welcome aboard.
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Old 03-31-2012, 11:38 AM   #9 (permalink)
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Injector pump timing

Hello,
I currently have a 1981 vw rabbit p/u and was wondering if you remember what the chilton manual recommeded for the timing?

Thanks,
Chris
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Old 03-31-2012, 04:13 PM   #10 (permalink)
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Hello Chris,
Yes, they recommend 0.036 to 0.038" for the NA, and interestingly, 0.038 to 0.040" for turbocharged engines. I set mine to 0.038".

BTW, I've been able to get 65MPG since, and almost every tank since has been over 60 MPG! I am working on some schemes hoping to get 75MPG.

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