my fuel mileage was a lie! - page 1 - Troubleshooting - VWDiesel.net The IDI, TDI, and mTDI source.

• my fuel mileage was a lie! by wdkingery on 24 Jul, 2011 12:58
• so it turns out, my speedometer reads high i noticed, altho i drive slowly, even when i was doing close to the speed limit people still blew by me.. and, after seeing the gas mileages ya'll are getting, mine is awfully high considering it's 305k+ miles old and all original.
  
  well, it's my daily driver, and i know where i'm going every day, so i never have my garmin in this car.
  
  well i checked my speeds against the GPS on my phone.. and the car reads slightly high, at times..
  
  so i did a quick road trip; brand new f250 called the trip home from costco 14.9 miles, and my car called that same trip home 15.4 miles.. 
  
  my speedo kinda.. dances a bit. but sometimes it's right, and sometimes it's not.
  
  anyone got advice?
• #1 by guy plain on 24 Jul, 2011 14:04
•  cable in the back loose?  do you have the stock trie size ?
• #2 by Luckypabst on 24 Jul, 2011 14:11
• The odometer is geared directly to the speedo cable (vs. the magnets and clock spring like in the speedometer) so any discrepancy there is likely due to incorrect tire size. Even with a clapped out, high reading speedo in my van and a slightly low reading speedo in my Rabbit, the odometer in both is damn near spot on.
  
  Chris
• #3 by ORCoaster on 24 Jul, 2011 17:20
• Real men own up to their mistakes and Real Good men take responsibility for them.
  
  You are a shining example of both.
  
  I have been chasing your 53 mpg on the fuelly page.  Seems we are similar in fillups and distance.  The off speedo might explain the one higher number on your history. 
  
  When I bought my Rabbit about a year ago I read some place that the speedos like to click back or ahead a bit as they roll through the gears.  I watched mine when it was up on a jack and sure enough, bump, bump at the zero mark.  So I tore it out and found the gear problem that is mentioned several places on this or another forum. 
  
  Like the man above says it is all mechanical.  Gears to cable back to gears.  Not much to go wrong except that tab on the tenths bumping the rest to little or too much.  My odometer is GPS dead on.  The speed is way wacko and I don't think it can be fixed as that is a function of the magnet that senses the turning of the cable.  Anyone know how to correct the high end of speedometer?  Other than to go pull another.
  
  The difference is small, 3 percent,  tires right sized
  
  
• #4 by wdkingery on 24 Jul, 2011 19:22
• Quote from: ORCoaster on 24 Jul, 2011 17:20

  Real men own up to their mistakes and Real Good men take responsibility for them.
  
  You are a shining example of both.
  
  I have been chasing your 53 mpg on the fuelly page.  Seems we are similar in fillups and distance.  The off speedo might explain the one higher number on your history. 
  
  When I bought my Rabbit about a year ago I read some place that the speedos like to click back or ahead a bit as they roll through the gears.  I watched mine when it was up on a jack and sure enough, bump, bump at the zero mark.  So I tore it out and found the gear problem that is mentioned several places on this or another forum. 
  
  Like the man above says it is all mechanical.  Gears to cable back to gears.  Not much to go wrong except that tab on the tenths bumping the rest to little or too much.  My odometer is GPS dead on.  The speed is way wacko and I don't think it can be fixed as that is a function of the magnet that senses the turning of the cable.  Anyone know how to correct the high end of speedometer?  Other than to go pull another.
  
  The difference is small, 3 percent,  tires right sized
  
  

  
  Hahahah I know right! I'm still chasin it too. I got that one with a healthy dose of the Grey bottle P/S stuff from walmart, and 300 miles of constant 42 mph (sight seeing in the country)
  Hopefully this thread will bring me some ideas for straightening this problem out, altho like you say it's only 3%
• #5 by Luckypabst on 24 Jul, 2011 19:23
• The speedo shop that gave me that nasty odometer gear also mentioned that my Rabbit speedo was clapped out (230k miles... go figure). Says the bushing wears, that the needle rides on, then the magnets get closer or further apart and you end up with inaccuracies in either direction.
  
  Chris
• #6 by ORCoaster on 24 Jul, 2011 21:31
• 
  So maybe the fix for me is just find a new cluster with a tach in it and upgrade the whole shootin match.  I did see on Craigslist that there is an available one and then an alternator combo all for about 100 bucks.  Not to bad of an upgrade.  I was thinking of one of those tiny tachs for the car and they are that alone and I wouldn't get the larger amperage alternator in that deal.
  
  What to do, What to do? 
  
  Right now I use my Garmin for a speedo and let the odometer do the tracking of miles for the tank since it is dead on.
  
• #7 by ORCoaster on 28 Jul, 2011 21:31
• I am Chasing no longer.  52 MPG on the way home tonight.  I screwed in the max fuel screw an eighth of a turn, maybe less to get a little bit more fuel in early compared to having to floor board the pedal when getting up to speed.  I have heard that you want the car to respond to the pedal quicker than I think mine was.  I don't blue smoke it until I drop it into third and rev the snot out of it.  I was able to cruise at 70-75 most of the way down I 5 and still had pedal to go.
  
  So I think I am going to leave it for a while and see if it was a fluke or the wind pushing me.  I did do about 100 miles of the 300 in the upper hills of Portland in stop and go traffic so who knows maybe I am actually hitting double nickels on the big road.  Whhooo hooo.
• #8 by wdkingery on 29 Jul, 2011 10:35
• Wow congrats! I am in no position at this point, the altho i've found some new additive I'm trying. I need to mess with fuel screw for the first time
• #9 by ORCoaster on 29 Jul, 2011 18:40
• My additive is 2-3 oz of Paraffin wax and 4 oz of Automatic transmission fluid in one gallon of diesel.  Let sit a week in the back.  Shake before adding to the tank before fill up.  At fill up refill little one gallon tank.  Easy as pie as they say.
  
  I changed out the transmission fluid today.  Only one quart instead of two and kind of silver looking.  This might not be a good sign.  I have been leaking a lot of fluid lately after I replaced the throwout bearing.  The big cap didn't seal right.  So I removed it and hammered the edges flat and goopped it up and tapped it back on.  Hoping that fixes it. 
  
  I also remembered that on the last tank I put on a new windshield.  Think that added a few mpgs?  All that silicone is gone from around the edges and there aren't any chips or cracks keeping the wind from flowing over the front.  It sure looks nicer from the inside when driving into the sun.
• #10 by wdkingery on 01 Aug, 2011 16:49
• Hey where do you get wax? And how does that work? I took yer advise and gave my fuel screw a spin (for the first time!.) (now to get that idle back down
• #11 by ORCoaster on 01 Aug, 2011 19:51
• Hey where do you get wax? I have my wife pick me up a box, 1 pound, at the grocery store.  This is the season people are canning so you should find it with the lids and jars.  Each of the four bricks is 1/4 of a lb or 4 oz.  I mark it off in quarters and shave off half a brick, 2 oz to the gallon I let it dissolve into.  The pound costs about four dollars and it treats 8 tanks or 80 gallons.  Not a bad additive, it won't clean valves or lubricate like some of the ads say the additives do but it does increase the fluid thickness and cetane of the diesel.  That is what I have come to understand about it.
  
  And that is how it works. 
  
  As for the idle coming down.  That is the screw on the throttle stop.  The one that is on the top of the pump on the back towards the engine.  Depending on which pump you have it is a 10 mm nut locking the threaded stud in place. or some adjustment on the lever on the back.  I didn't have to drop it down much from where it was at in the first place.
  
  Move the max fuel screw a bit at a time, like 1/8 turns it really is a sensitive setting.  At least mine seems to be.
  
• #12 by wdkingery on 01 Aug, 2011 20:15
• yeah it was quite sensitive.. i ended up winding it about half a turn haha i mean i can always turn it back.
  
  my idle is controlled by a 7mm stick that runs down to the cold start doo-dad, and the screw that stops the throttle lever from going back any farther. i have turned both down as far as they will go, and just barely have an acceptable idle.. i think i have turned my fuel screw too much. but my idle is just on the high side of acceptable, so i might just stick with it.. depends on how much this new found smoke hurts those precious mpg's..
  
  you were right tho; this car is seemingly much better to drive, and could get better mpg just cause i don't have to learn on it as hard to get going
  
  now back to this wax. does it dissolve at room temperature in diesel? i figured it would remain .. a chunk of wax at the bottom of my tank. you recommend this? i'm real interested in fun additives. at what point will too much jam a fuel filteR? and do i need to watch out in cold weather ?
  
  i think i'm going to steal your ATF/candle combo
• #13 by ORCoaster on 01 Aug, 2011 21:45
• The man asked the questions:
  now back to this wax. does it dissolve at room temperature in diesel? i figured it would remain .. a chunk of wax at the bottom of my tank. you recommend this? i'm real interested in fun additives. at what point will too much jam a fuel filteR? and do i need to watch out in cold weather ?
  
  i think i'm going to steal your ATF/candle combo
  
  The wax will dissolve best in warm diesel, some heat it up a bit on the stove.  Ahh not in my house.  So I keep the one gallon jug in the back of the car and you know how warm that can get.  Some just keep it in the sun outside their shed or storage building.  I shake it before pouring it in the tank and I have not noticed any chunks going in the filler tube.  Some tried to melt the wax and pour it into the filler tube.  Ahhh not a good idea as it cools and prevents filling later on.  Once I cut up the chunks in small half inch cubes and just dumped them in the filler tube.  I had to have the fill on real slow in order to get the diesel into the tank, once some of the wax dissolved the whole bunch went ca chunk into the tank.  Remember that the IP pump is moving fuel all the time in and out of the fuel tank, kind of recycling it.  So putting in a wax rich mixture at the first part of a tank fill does get mixed pretty good on fill up.  But continues to mix all the while you drive. 
  
  Using wax in the fuel will not clog a filter, it becomes part of the diesel, like dye in water, it won't filter out.  Now a word of caution for the cold weather.  It is wax, and if it starts to get cool what happens to wax?  So most folks use it until the temps start getting down in the 40s or so at night.  Then they switch to some sort of oil.  Living where I do I don't have that problem so I use it all year round. 
  
  I didn't come up with this trick, it belongs to Hagar, the hillbilly tuner.  Lives up in BC and swears by it.  His recommendation for determining if you have a good IP or a bad one is to add the whole pound to the tank in the summer and see what happens.  That much wax will really thicken up the fuel and your internal pressures will go up.  That and the cetane boost will really make the VW happy.  I am chasing his smileage numbers as well but don't think I will ever get his 70+.  Time is money to me, if I can keep my 50+ going and my speed at 65-70 then I am good enough.  At least until fuel goes to 5 bucks a gallon. 
  
  I am chasing an air dam for the car in hopes that makes a difference as well.  Might be .5 mpg but so be it.  From what I read the VW is about as aerodynamic as a brick and anything will help it cut the wind saves having to pedal down once you get to about 45 or so.  Thus I looked for and found one, now I just have to arrange a meeting to pick it up.  Not an easy do with most people coming and going this time of year. 
  
  
• #14 by wdkingery on 02 Aug, 2011 14:27
• Does it have to be paraffin?