D1 fuel economy

terryjm1

Well-known member
Jan 23, 2011
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I am sorry if this is a tired topic but when I searched I couldn’t find much on it.

I calculated my fuel economy the last 2 fill ups and am getting 16.5 miles per gallon. I think that is pretty good, particularly since the EPA numbers are 14-16.That is mostly 2 lane 45-60mph driving but in very “hilly” country. That was with a 96 5-speed with 4.0.

I haven’t tracked it in the automatic D1 but just based on how frequent that one requires a fill up, it think might be better.

Is 16.5 pretty standard?
 
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4Runner

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May 24, 2007
663
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Boise Idaho
If everything was perfect , I’d get 15 in my old 96. My 94 is 13/14 with a stick. My 04 gets 11/12. 😐 but has more power. I’d be thrilled with those mpg’s in an old Rover
 
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terryjm1

Well-known member
Jan 23, 2011
1,489
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That's really good. Are you using premium or regular?
Last tank was 88 octane (mid grade here). At high elevation, regular is 86 octane. If I go “down the mountain” I can get 87. I will give that a try next. I have not noticed any preignition issues. I believe with most driving being between 8000 and 9000 feet I may be able to get by with 87.
 

DarylJ

Well-known member
Apr 3, 2011
440
24
Doylestown, PA
That's a fine enough number that it's a good baseline. If you've not changed anything else (specifically tire size) and all remains close to that with similar driving driving that's great. If it changes a lot you probably need to look into an engine performance issue. Since yours is a 98 it will almost definitely set a code because it's most likely to be something dumb like an upstream O2 sensor that gets lazy, a stuck open thermostat that keeps you out of closed loop, etc.
 
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Tugela

Well-known member
May 21, 2007
4,760
563
Seattle
That's good economy - for a 27-year old brick powered by a 1970s engine based on an even older design.

A while back I stripped down my mostly stock 1998 Disco (roof rack, etc.) for a road trip to California and calculated fuel economy of 18mpg. That was all at 60mph on the interstate. I couldn't believe it.
 
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DiscoClay

Well-known member
Mar 18, 2021
443
89
Chapel Hill, North Carolina, USA
I am sorry if this is a tired topic but when I searched I couldn’t find much on it.

I calculated my fuel economy the last 2 fill ups and am getting 16.5 miles per gallon. I think that is pretty good, particularly since the EPA numbers are 14-16.That is mostly 2 lane 45-60mph driving but in very “hilly” country. That was with a 96 5-speed with 4.0.

I haven’t tracked it in the automatic D1 but just based on how frequent that one requires a fill up, it think might be better.

Is 16.5 pretty standard?
16.5mpg (US, not brit.. US gallon is smaller) is awesome. That makes me think you're going down hill both ways :)
 

DiscoClay

Well-known member
Mar 18, 2021
443
89
Chapel Hill, North Carolina, USA
16.5mpg (US, not brit.. US gallon is smaller) is awesome. That makes me think you're going down hill both ways :)
Fun fact:
The reason for this difference dates back centuries when the gallon was first defined. The US gallon is based on the old wine gallon used in England prior to 1824, while the UK Imperial gallon was defined in 1824, at a time when the UK wanted to standardize various liquid measures and chose a different base unit. The Imperial gallon was designed to hold exactly 10 pounds of water at a specific temperature and pressure, which is more than the old wine gallon could hold. The US, on the other hand, continued using the older definition.
 
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Tugela

Well-known member
May 21, 2007
4,760
563
Seattle
Fun fact:
The reason for this difference dates back centuries when the gallon was first defined. The US gallon is based on the old wine gallon used in England prior to 1824, while the UK Imperial gallon was defined in 1824, at a time when the UK wanted to standardize various liquid measures and chose a different base unit. The Imperial gallon was designed to hold exactly 10 pounds of water at a specific temperature and pressure, which is more than the old wine gallon could hold. The US, on the other hand, continued using the older definition.

Great knowledge nugget. Since this is Discoweb and thread drift is part of its DNA, let's take this tangent a little further. The only countries still not using the metric system are the USA, Liberia, and Myanmar. I wonder if we'll ever get with the program.
 
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DarylJ

Well-known member
Apr 3, 2011
440
24
Doylestown, PA
Great knowledge nugget. Since this is Discoweb and thread drift is part of its DNA, let's take this tangent a little further. The only countries still not using the metric system are the USA, Liberia, and Myanmar. I wonder if we'll ever get with the program.

I don't think it will happen too soon or all at once, but the US is increasingly metric. Anyone in science or engineering is learning in metric and have been for decades, packaging almost universally has metric equivalents........
 
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StangGT5

Well-known member
Feb 4, 2019
295
131
Atlanta, GA
16mpg sounds like a healthy D1 to me, especially in hilly terrain. I can't remember getting more than 14 or so in any D1, but I was always 70mph+ on highways.

My 04 D2 maybe gets 14mpg. Heck, my 13 LR4 gets 15mpg combined, though it's 90% city and is modified.
 

discostew

Well-known member
Sep 14, 2010
7,725
1,022
Northern Illinois
I think it’s the hills getting you Terry. I would expect them to take more. So I think that’s good. The best I could do with a Disco here was about 18. I think the average was maybe a bit less.
I try to get good mileage in my Cruze. It gets about 46 mph at its very best, average is probable 42. I notice wind and rain effect it a lot. I think the higher altitude is going to make your Baro sensor want to add fuel also.
 
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terryjm1

Well-known member
Jan 23, 2011
1,489
375
It’s a stock but low miles (27,XXX) 4.0. The only non-stock aspect that may affect fuel economy is it has new Ford type injectors that produce a finer spray pattern.

On the 16 mile 5000 feet drop the accelerator pedal is never touched. Engine braking is standard just about the whole way. down. Going back up it really works hard, probably 50% accelerator in 3rd gear mostly and a few short runs in 4th on the less steep sections.

The most recent trip on that route, I went back uphill with the AC on and it moved the temp gauge past the halfway mark, close to 5/8 I’d say, and made me a bit concerned. In the 1000 ish miles I have driven it since I got it back on the road, I’d never seen it go above the 1/3 point. I pulled over for about 5 minutes and is cooled back down and stayed down the rest of the climb. The area I stopped, about half way, is also where the outdoor temperature really starts to drop. Where I started it was 93 degrees. It is in the high 60s by the time I get to the top. It’s the first time I made the climb with the AC on but also the first time with 87 octane. I wonder if there is any correlation to the octane. The AC fans were operating. The coolant tank was where it should be as well. The radiator came out of the same donor vehicle the transplanted engine came from. It looked very clean from what I could see from the hose ports. I’m going to repeat the trip soon but with my scanner plugged in so I can see the actual digital temperature.
 

p m

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Apr 19, 2004
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The only countries still not using the metric system are the USA, Liberia, and Myanmar. I wonder if we'll ever get with the program.
I remember being put off by that when we moved to the U.S. But then, in two years of mechanical engineering school, I started to appreciate that scaling of fasteners with the load requirements is a lot easier with powers-of-two-fractional system. With just a little skill one can get away without a calculator.
 
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Disco95

Well-known member
Mar 20, 2020
51
21
Portland, OR
Maybe not directly comparable to your GEMS truck, but our stock 95 14cux 5sp approaching 200k averages 12. About 11 around town, 13 mixed, and 17 highway. Haven’t done extensive freeway driving with it. PO claimed 18 mph for his daily freeway/hwy commute, and I tend to believe it. 50-60 seems like the sweet spot.

The D1’s been one of the oddest vehicles I’ve owned as far as mpg—I usually have no idea what a tank’s going to return. Loafing around town at <2k rpm might be 9mpg one tank or 13 the next. No rhyme nor reason where all that gas is going! Our best tank came when I felt like I was pushing it on rolling hills at 55-60mph.

Anyhow, 16.5 sounds good but not unrealistic.

Cheers,
joe b
pdx or
95 Disco V8 5sp
 
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robertf

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Jan 22, 2006
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keep in mind the odometer is about 10% fast with factory tires, so adjust MPG claims accordingly

It is perfect with 235/85s
 
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