Savin' fuel test

82vdub · Post by **82vdub** » Wed Jul 23, 2008 11:16 pm

On this last tank of fuel, I decided to do a test in my 82 Rabbit to see how much I can improve my fuel mileage by making two easy to do changes. One was to push in the clutch when the light turns yellow, instead of letting the engine slow the car down in that particular gear it was in at that time, or push the clutch in towards the bottom as I go down the large bridge in town before I exit the highway going to work. The second was to drive 60 MPH on the highway the short distance to and from work instead of the normal 65-70. I get home tonight with the gas gauge 2 lines above empty (reserve empty), and the furthest I've let it go before was down to one line above empty. Previous maximum was 455 miles to the tank, with normal typical max tank roughly 430 miles (also read below). This time I got 514.1 miles on the trip meter for this tank full of gas - nearly 80 miles further! If I didn't have to go out of town tomorrow, I would be driving it to work and putting another 12 on it before I need fuel.

Since my odometer registers approximately 92-93% of actual mileage (compared to the mileage markers along the highway). Taking that into consideration, that's 552.8 miles on a tank of fuel, which wasn't as low as I have let it go before on previous tests. The fuel tank is supposed to hold 10 gallons, but I've put in close to 11 when the tank has been this low and filling it to the brim, so that is in excess of 50.25+ MPG. Not too bad for a car with over 1/3 million miles on it.

I didn't tune anything different and am not testing for maximum smileage, but just wanted to see what two simple non issue changes would do for around town mileage. Was plesantly surprised. Time to fire up the old big block and spend some of that fuel savings

VWCaddy · Post by **VWCaddy** » Thu Jul 24, 2008 10:32 am

Yep, I have been using the upshift light and it does seem to save about 10% on fuel consumption around town.

JRM · Post by **JRM** » Thu Jul 24, 2008 9:12 pm

on my reccord 63MPG trip i turned the key off on long downhills so the fuel stop switch on the pump would close, but it kept locking up my friggin stearing wheel even with the key in the ignition almost causing death but this helped big time- so much so im thinking about wireing a push button to the stop switch so i can shut the pump off 100% on every downhill TDI style

tylernt · Post by **tylernt** » Fri Jul 25, 2008 12:09 am

JRM wrote: but it kept locking up my friggin stearing wheel even with the key in the ignition almost causing death but this helped big time- so much so im thinking about wireing a push button to the stop switch

Put it on the shifter like Mad Max's blower. That would be cool.

MPalm · Post by **MPalm** » Sun Jul 27, 2008 5:14 am

ItÂ´s fun to do stuff like that and see that it has effect on mileage even if the mileage is as good as it is to begin with.
My Skoda usually is at 5.2L/100km = 45mpg
My last fill up was 4.92l/100km = 48mpg and I didnÂ´t really do anything special, I think the main thing was that I never drove over 100kph.
That was the first time ever that I got under 5L/100km, not many cars are able to beat that with a "normal" driving style..

82rabbitdiesel · Post by **82rabbitdiesel** » Fri Aug 01, 2008 3:32 pm

JRM wrote:on my reccord 63MPG trip i turned the key off on long downhills so the fuel stop switch on the pump would close, but it kept locking up my friggin stearing wheel even with the key in the ignition almost causing death but this helped big time- so much so im thinking about wireing a push button to the stop switch so i can shut the pump off 100% on every downhill TDI style

so you would push in the clutch w/ the switch off to the bottom of the hill and when you approach the bottom of the hill let out the clutch and bump start it? would it be easier to take out the locking pin on the steering column or get one that didn't have one like my 82? i don't think i have a fuel stop switch on mine but i might.

VWCaddy · Post by **VWCaddy** » Fri Aug 01, 2008 4:00 pm

I've been thinking of adding a relay up front by the pump. Then have the relay controlled by a switch back in the cab to send power to the fuel stop solenoid. Then the switch could be used both to shut off fuel for downhill braking as well as a security device to prevent theft. Keep the switch in an out of the way location and no label on it and that would probably keep the average thief from starting the engine.

tylernt · Post by **tylernt** » Fri Aug 01, 2008 4:40 pm

On fuel-less engine braking: will the IP or stop solenoid sustain any damage or wear from long periods of the pump turning with the solenoid off?

On coasting and bump-starting: will the drivetrain or clutch sustain any damage or wear doing that frequently?

VWCaddy · Post by **VWCaddy** » Fri Aug 01, 2008 7:02 pm

tylernt wrote:On fuel-less engine braking: will the IP or stop solenoid sustain any damage or wear from long periods of the pump turning with the solenoid off?

On coasting and bump-starting: will the drivetrain or clutch sustain any damage or wear doing that frequently?

No problem with the fuel cut solenoid being open, all that does is let the fuel just return to the tank. Basically it releases the pressure on the pump (so nothing gets injected) and sends 100% of the incoming fuel back to the tank. No need to bump start, at least for down hill engine braking, just leave the engine in gear, like normal, only shut down the fuel supply. That is my main goal, getting a little extra engine braking down steep hills.

Not sure about the benefits of coasting with the engine stopped, whether you can do that enough to make much difference compared to coasting with the engine idling.

tylernt · Post by **tylernt** » Fri Aug 01, 2008 7:16 pm

VWCaddy wrote:Not sure about the benefits of coasting with the engine stopped, whether you can do that enough to make much difference compared to coasting with the engine idling.

And the associated problems of heatsoak from stopping the water pump and low oil pressure from stopping the oil pump.

JRM · Post by **JRM** » Sat Aug 02, 2008 2:11 am

yeah i tired both, keeping it in 5th gear and killin the fuel supply is best, as when i coasted for 4 miles in netural traveling from 6,000 FT to sea level i started to get a vibration- i think the tranny goes dry without the engine running, but not 100% sure

surfcam · Post by **surfcam** » Sat Aug 02, 2008 12:30 pm

Your right. I remember reading that the 020 tranny can't be towed in over 50 miles per hour and every 200 mile it should be put in gear and run. Something like that anyway. There's a shaft in the tranny that doesn't see oil in neutral. Doesn't sound like a good vehicle to be towing without a dolly.

Post by **Fatmobile** » Sat Aug 02, 2008 1:53 pm

I had never heard that.
I suppose pulling the axles and putting stub axles in the bearings would be the way to do it, if you were using a towbar.

surfcam · Post by **surfcam** » Sat Aug 02, 2008 2:27 pm

I just checked my mark II Bently page 28 and I was right about the speed but wrong on the distance its only 50 miles.
In Canada its illegal to coast your car in neutral. Chances of being cot nil.