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Fuel consumption help
by
gabo
on 07 Mar, 2011 09:46
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Hey everybody.
Finally, this site has lifted it's registration lock!
I have posted this in the Vortex, and although I got some feedback, I didn't solve my problem.
I have a '93 Passat GL AAZ with 310 000 Km on the clock. I am currently doing between 8.5 to 10 liters per 100km (roughly 26 miles / Gallon). The best I managed was 800km on 69L of fuel. 400km of that was very mellow Highway cruising.
-I have awesome compression (only need to put the block heater below -15c, or else it starts on a quarter turn, always. But I always plug it in anyways)
-I have ''decent'' power.
-The tires are heavy studded snow tires. (P195 / 65 R15)
-All 4 wheels spin freely. No brake rub. No sticky hand brake.
-Air box is free and clean. Air filter is dirty, but acceptable.
-There is no fuel leaks that I know of.
-Fuel filter is new (less than 5k)
-I always fuel at a busy Shell gas station / almost truck-stop.
-I ain't got no junk in ma trunk, ya hear? I travel light.
-The tach never worked since I got the car.
-My daily commute consists of dropping off my daughter to the sitter and going to work. there is no stop 'n go traffic, slightly rolling hills, 70kph average speed. I let 'er idle for 30 seconds before leaving.
-I'm not out there chasing rice!
I know the Passat is a bigger car. Yet I have seen AAZ's in Jetta's do 6L/100km to 5L/100km. The previous owner stated that the worst he's done was 7L/100km.
I've changed my driving habits. I shift a lower RPM's. Plug it at night. I've tried some injector cleaner... No major difference.
I'm at a loss here! any help would be greatly appreciated!
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#1
by
Vincent Waldon
on 07 Mar, 2011 10:00
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Things I see in your config that will definitely impact your economy include:
- you're on winter fuel (10% drop in BTUs and hence fuel economy)
- winter driving conditions: heavy winter tires, nice wet New Brunswick snow to push thru, engine takes extra time to get to operating temperature
- not really high-way driving conditions if you are averaging 70 km/h... slows warm-up as well
- yup, Passat is slightly heavier than a Jetta or Golf... a bigger factor the more speeding up and slowing down your commute makes you do
My opinion: grin and bear it until the summer (summer fuel, summer tires, summer ambient temperatures) and get 'er out for a highway road trip where you can sustain 90 km/hr for a couple of hours. Those are the driving conditions under which you can expect 5-6 L / 100 km.
One thing you *can* confirm now is the timing... for your engine somewhere between 1.00mm and 1.05mm is probably the sweet spot for power and economy. In my mind you've definitely covered off on all of the major bases.
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#2
by
gabo
on 07 Mar, 2011 16:04
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Thanks Vincent.
I might sound like a complete idiot, but general winter conditions with my tires and winter fuel can add up to a 3-4L/100km loss in efficiency? Kinda steep, no?
Anywho... I guess this will give me one more reason to look towards spring. We've been having the worst winter...!
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#3
by
Vincent Waldon
on 07 Mar, 2011 17:30
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Well, if your engine/car are capable of 7 and you're getting 8.5... that's only 1.5 l more over 100 km... definitely within the range of winter fuel, winter tires, winter roads, long warm-ups, and not really being at highway speeds for sustained periods.
And yup, these cars, being as... shall we say "underpowered" or perhaps "right-powered" as they are... don't have a lot of extra umph to muscle thru seemingly small things like dragging brakes, poor wheel alignment, or big winter tires and snowy roads without noticing.
My uber suggestion is really that winter is a tough and discouraging time to be checking/thinking about fuel economy... *so* many factors, and you've controlled most of the ones you can.
I still recommend checking your timing now... it can have a major impact, and if your last mechanic used the "official" spec it's very very conservative.
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#4
by
Wayland
on 07 Mar, 2011 19:22
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if your last mechanic used the "official" spec it's very very conservative.
This is very true. I have the exact same car as you, and went from 47 to 53 miles per gallon (imperial) just by bumping the timing up from whatever it was set at (.88mm I think is stock) to 1.05mm. My thermostat wasn't closing all the way either, and by replacing it I got another couple of mpg too.
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#5
by
8v-of-fury
on 08 Mar, 2011 07:20
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I mean your really only down %15 efficiency.. Your doing well for having those heavy studded tires, AND winter fuel.. I think winter fuel can account for %10 by itself, IIRC.
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#6
by
rdezsofi
on 08 Mar, 2011 08:12
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I have a 1.6 disel NA....which are very reactive to any changes. I've played with it over thousands and thousands of miles getting it to 53 mpg. The number one thing that affected mileage was the tires. Going back to the stock tire size increased about 4.7 mpg. (I had low profile 50's on 15 inch rims.) Synthetic gear lube in the tranny added 2 mpg. Running synthetic LubroMoly oil 5w30 made an increase of 3.2 mpg over 15w40. When it drops about 2 mpg, I throw in a new air filter and it goes right back to where it was. Keep in mind I drive the same 120 mile roundtrip to work every day, 95% freeway at 65 to 70 mph, which provides the perfect testing ground. Lowering the vehicle 1 inch provided 2.4 mpg, also. Took off the luggage rack and I gained a whole 1.3 mpg. To maintain fuel economy in the winter, I run the Power Service stuff.....the only one I have found to overcome the lower power winterized diesel. If you fuel up with B10 or B20 biodiesel, as mandated in some large cities now, I lose 10% of my fuel mileage....so I avoid the stuff like the plague.
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#7
by
gabo
on 08 Mar, 2011 14:58
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I've wanted to get my timing checked, but my VW-tech cousin said if it started and drove fine, it shouldn't be off enough to significantly affect my mileage. I gues he's not enough of a diesel nerd...
I was turned on by this car because of it's condition, the overal size, and the fact that it was ''supposed'' to be cheap on fuel. If you take in account the price of fuel at the moment (1.26$ / L) it costs more to run per KM than my wife's Mazda3.
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#8
by
8v-of-fury
on 08 Mar, 2011 15:06
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I think it will start and run just fine down at like 0.80mm.. maybe even lower!
I would get that thing timed up to 1.05mm at the least.. maybe more even.
Youčll be surprised what adjusting the timing can do. Do you have a tachometer in this car, do you know what revs your spinning on the highway.
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#9
by
maxfax
on 08 Mar, 2011 15:50
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but my VW-tech cousin said if it started and drove fine,
Timing can be off and they'll start and drive decent, but not necessarily optimally.... I;d check it to be sure, and advancing is beyond the spec has done wonders for these engines.. Ideally is to find yourself an old timer who can set it by ear, then record that setting...
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#10
by
gabo
on 08 Mar, 2011 16:05
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I think it will start and run just fine down at like 0.80mm.. maybe even lower!
I would get that thing timed up to 1.05mm at the least.. maybe more even.
Youčll be surprised what adjusting the timing can do. Do you have a tachometer in this car, do you know what revs your spinning on the highway.
The Tach never worked sinced I go the car. The PO told me he put a gaser cluster behind the stock diesel ''graphics''. So my glow plug light doesn't work either. I've gotta go by ear!
I've done some research into this. I have to get a converter box from the W terminal on the alternator to the cluster... or find a diesel cluster! I'm kinda tempted by one of them fancy retro style chrome-bezeled tachs, though!
I'll look into having the timing checked. It'l give me a good excuse to have a good look at my timing belt too.
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#11
by
Vincent Waldon
on 08 Mar, 2011 16:11
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It'l give me a good excuse to have a good look at my timing belt too.
Any excuse will do!!
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#12
by
gabo
on 21 Mar, 2011 08:22
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I believe I have found the problem...
My landlord pointed out that my car was leaking oil on the asphalt. He probably noticed now that the snow is gone ( we got a total of 16 feet this winter). I never noticed since I always park my car in that spot and never cared to look under my car since I do my maintenance elsewhere. I double checked my fuel lines again and saw nothing. I figured it must be oil slowly seeping from the oil pan.
In the past I have noticed a bit of smoke coming from under my hood but never though anything of it. I always figured it was either snow or water being thrown on the exhaust or other hot bits. But this morning was dry. And I don't know if it was because of the weather but there was a lot of smoke emanating from under the right side of my hood. I popped the hood and followed the smoke, with a bit of light I noticed a steady drip (one drip a second) of diesel coming from behind the fuel pump, pooling between glow plugs 1 and 2 (3 & 4?) and evaporating in a huge puff of smoke.
Please tell me this can be remedied by tightening a banjo fitting!
I've been wanting to re-build my fuel pump for a while, maybe even send it to Gilles, but sincerely for the moment I'd prefer a simpler alternative!
I'll have a closer look during my lunch break, I'll try to see exactly where it's leaking from on the pump.
Any hints or feedback will be treated like gold!
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#13
by
dieselweasel
on 21 Mar, 2011 09:26
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Behind the injection pump will be cylinders 1 & 2. Check the soft return hoses between the injectors first...that's my first guess. Common points of leakage on the pump itself include the cold start cover, the aneroid vent, and the distributor head o-ring... Have a look and let us know.
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#14
by
gabo
on 21 Mar, 2011 12:08
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It seems to be leaking from a bolt angled about 45degrees under the pump, situated about half way between cylinder 1 and 2. I can barely see it, even less get a wrench to it... any suggestions?