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Topic: 1998 TDI with MPG problem (Read 2202 times) |
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redarrow007
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folks out there can you help me, i have a 98 TDi estate that only does 24mpg. i checked out the OBD and cannot find any problem, the car runs OK with no problems. so i cant find any faults. any ideas as to what to look for as its costing me more than my volvo 940 to run....cheers
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tonyboy
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Re: 1998 TDI with MPG problem
« Reply #1 on: Apr 23rd, 2010, 12:05am » |
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Fuel leak somwhere.......... maybe.........
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I think i'm going, erm what do you call it..... Senial.... 
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redarrow007
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Re: 1998 TDI with MPG problem
« Reply #2 on: Apr 23rd, 2010, 12:06am » |
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no not a fuel leak, i dont think ive checked the fuel lines....thanks
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amigafan2003
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Re: 1998 TDI with MPG problem
« Reply #3 on: Apr 23rd, 2010, 9:38am » |
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24mpg driving where? If it's a town car then that's probably about right. If it spends most of the time on the motorway @ 70mph then you're correct, something is amiss.
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Highlander
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Re: 1998 TDI with MPG problem
« Reply #4 on: Apr 23rd, 2010, 10:12am » |
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Brakes binding?
tyre pressures?
Thermostat ok?
dirty injectors, EGR, air filter etc can all have a major effect on mpg
Is it an auto?
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on Oct 17th, 2011, 12:35pm, Simmo wrote:I give up !  Too much for an old boy! |
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redarrow007
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Re: 1998 TDI with MPG problem
« Reply #5 on: Apr 24th, 2010, 12:15pm » |
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thanks for the replys.. checked brakes and stat and most of the norm,,,the only thing i can think of is the injectors. the mpg is similar in town and on m/ways
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Mike H
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Renault Clio
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Re: 1998 TDI with MPG problem
« Reply #6 on: Apr 25th, 2010, 2:37pm » |
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What mpg should a diesel normally do?
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Mike H
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Robzere31
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Re: 1998 TDI with MPG problem
« Reply #7 on: Apr 25th, 2010, 5:21pm » |
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on Apr 25th, 2010, 2:37pm, Mike H wrote:What mpg should a diesel normally do?
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I tend to get around 35-40 mpg out of mine. Average around 420-450 miles out of a tank.
205K on the clock, although it's had new injectors recently.
If driven like a grandad on the motorway 40 mpg is easy to achieve, giving it a bootful though drops it to around 35mpg. lol
How are you working out your MPG? tank to tank?
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redarrow007
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Re: 1998 TDI with MPG problem
« Reply #8 on: Apr 26th, 2010, 1:34am » |
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yes tank to tank,,,,
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Mike H
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Re: 1998 TDI with MPG problem
« Reply #9 on: Apr 26th, 2010, 8:18pm » |
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Interesting...
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Mike H
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tonyboy
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Re: 1998 TDI with MPG problem
« Reply #10 on: Apr 26th, 2010, 8:46pm » |
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Maybe filling the tank up to full, then refill when it's nearly empty, and so on then you get miles per tank.........
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I think i'm going, erm what do you call it..... Senial....
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redarrow007
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Re: 1998 TDI with MPG problem
« Reply #11 on: Apr 27th, 2010, 1:27pm » |
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thats what ive been doing tony....
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Mike H
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Re: 1998 TDI with MPG problem
« Reply #12 on: Apr 27th, 2010, 1:31pm » |
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Can be a problem with accuracy for instance if you drive 'til the low fuel indicator comes on, but then how much "reserve" is there? Doesn't mean you've used the whole 70 litres
I've done it using partial filling, IIRC how it goes is you arrive at filling station, make a note where the fuel gauge needle is. Put in X number of litres, a round number, and make a note of it. Zero the trip.
Drive until fuel gauge reads same as before, and make note of miles from trip. Voila. You now know how many litres covered how many miles.
To convert litres to gallons divide by 4.55
It assumes of course the speedo and trip meter are accurate
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Mike H
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Highlander
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Re: 1998 TDI with MPG problem
« Reply #13 on: Apr 27th, 2010, 9:14pm » |
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I wouldnt go by the gauge Mike.
best way is to fill the tank, reset the trip, then once its nearly empty refill it and note how much fuel it takes, which is what Redarrow has done.
bear in mind the trip meter shows around 10% less than the distance actually covered.
eg if the trip shows 50 you have done 55 miles
this alone wouldnt account for Redarrows low mpg though, there must be something else affecting it
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on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
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redarrow007
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Re: 1998 TDI with MPG problem
« Reply #14 on: Apr 27th, 2010, 10:37pm » |
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thank chaps, ive assumed the trip is 100% spot on ive got 3 programs on my iphonne for cac the MPG. all are set for UK miles per gallon, with liters input. all 3 programs say around 24 per gallon. i went up to scotland in nov last year and found it was doing 25mpg on the motorway home that was at 80mph none stop.
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Mike H
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Renault Clio
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Re: 1998 TDI with MPG problem
« Reply #15 on: Apr 28th, 2010, 12:19pm » |
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It does seem rather rediculous, I mean the 2 litre petrol should do at least 30 mpg cruising like that so what's the point having a diesel! Albeit 2.5 L (?)
I think the formula is IIRC:
mpg = miles / (litres / 4.55)
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Mike H
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Mike H
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Re: 1998 TDI with MPG problem
« Reply #16 on: Apr 28th, 2010, 12:22pm » |
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A more accurate constant for the litres conversion is 4.54609
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Mike H
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Highlander
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Re: 1998 TDI with MPG problem
« Reply #17 on: Apr 29th, 2010, 7:02pm » |
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Is it an auto?
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on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
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redarrow007
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Re: 1998 TDI with MPG problem
« Reply #18 on: May 4th, 2010, 10:54am » |
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yes its a big old auto
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Highlander
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Re: 1998 TDI with MPG problem
« Reply #19 on: May 4th, 2010, 12:16pm » |
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Ahhh thats helps...
whats your RPM at 70 mph?
It may be running in the wrong gear or has a faulty torque convertor
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on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
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