Pickup MPG

[Dat Lurka]

I wonder what my mileage will be like with efi.

[zrex]

This is what i get 85 stock 4x4 17.5 mpg and a 75 620 with 37mm s.u's around 23 mpg. Not great but better than my 2005 Jeep Grand Cherokee 4x4 with the 5.7 hemi that gets 14.5 mpg.

 

Rex

[Cardinal Grammeter]

Just wanted to ad I had a 72 510 and got in the 20's - nothing exciting.

 

However, I had a 1400 pushrod B210 that was a 74 I think (maybe a 76 ???) and I distinctly remember it had the most precise 4-spd shifter I have ever driven still to this day and it got 44 mpg driving from Pittsburgh to New Jersey on the PA Turnpike.

 

I loved that B210 but it eventually rusted in half like they all did in the Rust Belt.

 

I just got this 74 620 and am excited to "get back to my roots."  What is really freaky was that back then, I got some manuals that I never got rid of.  One of them was a 1974 Datsun 620 Pickup Shop Manual."  Yes, can you believe it, I've had the shop manual for the truck I would buy for FOURTY YEARS!  What is weird is that I also have an engine shop manual for the L20, L16, and a smaller one, but no L18.  It appears to be all the OHC engines so I don't get it.  What happened to the L18?

 

I'm really excited to get this 620 on the road because it is going to be a very cool ride.  I won't mind a little more respect on the road that I get with my 1991 Geo Metro (!).  And if this isn't sick, I don't know what is, but I also have a 1963 Factory Supercharged Studebaker Super Lark w/R2 engine AND a modded 1996 Dodge Viper with over 90k miles.  I got the Viper when I was rich and now I'm broke, so its Metros and now a Datsun for me these days.  I hope to hold onto the Viper but don't know if it will be possible.

[RatVonDude]

24 mpg tops on a 1972 521, thats if my miles gauge is even accurate. If you remove the spare tire and bumper you might save 25 cents at the pump. Can't tell if it got better mileage with the stock hitachi vs. weber 32/36.

[RTB]

[ggzilla]

On topic, it's the right thing to do.

[Icehouse]

My Datsun work horse got 39.7 MPG's on the way back from Canby.  It's the only long trip I've made and actually done a good job calculating the milage.  I went as far as google mapped the directions flowed them to the T and filled my gas tank so I could see the fuel in the same place in the neck on all the fill ups.  Can't image what it would do with a 5 speed in it!  On the sweeper speedometer, at freeway speeds the  needle is over a background with red stripes.  My bro used an iPhone app for measuring decibels it's louder in my truck than in a 747 in flight….   It's my daily but work is only 1.5 miles away and I don't usually go over 35mph :)  

 

 

[ggzilla]

That's great mileage. They get 35mpg normally but with larger tires will get better economy.

[smoke]

Mine gets 74.3 mpg. But, I only measure it when going downhill, so that might throw off the accuracy some.

[ggzilla]

Which engine do you have? The 1.2 liter that icehouse has only gets in the 30s. With a 5-speed it will probably get around 45

 

I had the same truck but with 1.5 liter and untuned twin sidedraft carbs was only getting 22 MPG.

[Icehouse]

David my truck has a much lower coefficient of drag than your old truck, I think that plus I drove about 60mph max on the way back.  

[Cardinal Grammeter]

Update on my 74 620 and some qualitative gas mileage comments - it sure guzzles at 75 mph.

 

My 74 has been my daily driver now for over 3 months. 

 

I've taken it for many back road joy rides that are 30-45 minutes long - the gas gauge doesn't move much each time.

 

Then I had to take on the interstate for about 60 miles and driving 70-75, I almost ran out of gas - I started with 1/2 tank and just when I got there I realized I was on Empty which was a small problem since I was out in the boonies.

 

I have no idea what rpm that L18 turns at 70 but I'm guessing 3500-4000 maybe.

 

I also know that when driving a stick with MPG computer, if you use a lower gear, no matter what the reason, it kills the mpg substantially.

 

I didn't have a chance to fill it up to calculate mileage (that is another problem, no matter what fillup nozzle angle, gas shoots out the filler if anywhere near wide open on the pump), but I'm guessing 15 mpg which would make sense:  4 gallons in one hour.

 

I really like the 620 and around town it's cool to be able to keep it in 4th basically forever - almost like an automatic.  Poor thing is screaming for a couple higher gears though.

 

Oh, and at >70 mph, I'll bet the Ll20 clutch fan is worth at least 1 mpg in savings.

[datzenmike]

If I drove my L20B 5 speed  620 carefully when crossing Canada I could get 28MPG or 24.1 US MPG. Driving carefully meant not flooring it every time I went up any hill trying to maintain 50 MPH. 

[Cardinal Grammeter]

Absolutely about maintaining speed up to the top of a hill and summit.

 

I drove a Scion that wasn't that old and it had an instantaneous MPG display.

 

I learned two amazing lessons:

 

GAS PEDAL POSITION:

 

I was shocked that MPG was simply a function of gas pedal position :confused:  - it didn't matter if you were going up or down a hill or what the load was on the engine.  This car was capable of breaking 50 mpg on the level at 50 mph, however, the gas pedal position was so minute, it was not humanly possible to hold it there - its like you needed a vernier pedal.

 

DOWNSHIFTING:

 

The other thing I noticed was that under no circumstances could you downshift and come anywhere close to the mpg you were getting before the shift.  This tells me the 4-speed 3500ish rpm is a disaster for mpg.

 

NOTE:  I noticed this because I was trying to get the ultimate mpg on a 2 hour trip across the hills of SW PA on 2-lane state highways.  I did 44.5 mpg on a car that was rated 34 mpg highway.  Friend said the mpg skyrocketed only after about 10k miles of break in.

[hobospyder]

properly inflated tires help as well. i made sure my tires were up in pressure on the trip to oregon last month and jumped from 19ish mpg to 24 or so

[Rjawm]

 

 

I drove a Scion that wasn't that old and it had an instantaneous MPG display.

 

 

I really hope it wasn't a TC model, or one of the other Drive by Wire equipped Scions.  That'd kinda put a damper on the results of the findings if it didn't even have a throttle cable.

[bilzbobaggins]

I really hope it wasn't a TC model, or one of the other Drive by Wire equipped Scions. That'd kinda put a damper on the results of the findings if it didn't even have a throttle cable.

Could you spoon feed me on this?

[Rjawm]

Could you spoon feed me on this?

 

Well, I'm not seeing the correlation of the amazing findings he's mentioned when the car he's mentioned is not only EFI but is also effectively a computer controlled accelerator pedal.  There is no throttle cable connecting the pedal and the throttle body in a Drive by Wire equipped vehicle.  It's essentially a potentiometer controlled by the pedal that electrically sends the signal to the servo on the throttle body to open or close based on throttle position.  Add to that it's reaction delay/time is factored into the emissions programing of the vehicle and there are even more issues with the comparison made of pedal position to effect on MPG. 

 

I guess I fail to see where the comparison of throttle position on a 70's era Datsun truck and a unknown year, but newer, Scion can have accurate info shared between them, that's all.

[bilzbobaggins]

Well, I'm not seeing the correlation of the amazing findings he's mentioned when the car he's mentioned is not only EFI but is also effectively a computer controlled accelerator pedal. There is no throttle cable connecting the pedal and the throttle body in a Drive by Wire equipped vehicle. It's essentially a potentiometer controlled by the pedal that electrically sends the signal to the servo on the throttle body to open or close based on throttle position. Add to that it's reaction delay/time is factored into the emissions programing of the vehicle and there are even more issues with the comparison made of pedal position to effect on MPG.

 

I guess I fail to see where the comparison of throttle position on a 70's era Datsun truck and a unknown year, but newer, Scion can have accurate info shared between them, that's all.

Wasn't meant to be argumentative. Just curious. I bought my ex wife a 2012 civic. I was always dubious of the back roads fuel mileage. If I peddled the car it was around 50 mpg zipping down hills and peddling up. The math came back correct doing it manually but I was never sold in the end

[Rjawm]

Didn't know my posts seemed argumentative either. Sometimes people make such apples to oranges comparisons on car forums I guess I wanted confirmation I was reading his post correctly is all.

 

The post went from talking about an old Datsun pickup to a newer Scion and what seemed to be a comparison of MPG's via driving habits, so I wanted clarification.

[bilzbobaggins]

Kool. I'm druuuuuuuuuuuuuuuunk. Smile

[Cardinal Grammeter]

70 Datsun and 00 Scion are still internal combustion engines subject to the same problems of fueling, timing, etc.

 

One thing to keep in mind, when held in a gear, no matter what the speed (or throttle angle), you get only so many revs per mile.  Those revs per mile are constant.  I would like to confirm mpg = function of throttle angle, however I only have experience with the manual Scion and an automatic HHR. 

 

There also seems to be a general relationship lower engine revs and higher mpg which is obvious when you get worse mpg in a lower gear.

 

All of this strongly suggesting a double overdrive transmission would be awesome for mpg.

______________________

 

NOTE:  All these observations were made at low rpm and low throttle angles.  Engines are highly non-linear, so these relationships may not hold at high rpm or high throttle angles.  Specifically a 620 turning 3500-4500 rpm on the highway.

[datzenmike]

This is all subject to the 'you can't get something for nothing law'. Gasoline contains a finite amount of energy and this will only move a 620 so far. You can't expect an idling engine to pull you up a mountain in 5th gear by the skillful use of several overdrive 5 speeds and a 1 to 1 differential. At some point the engine isn't making enough power to pull you along and this is why you have 4 speeds. You have to make power proportional to it's need. If you need 12 hp to pull you along at 40 MPH through the wind resistance... you need 48 hp to go 80 MPG... 4 times to double your speed.

 

 

Weight is the biggest factor in MPG then wind resistance assuming all other things like drivetrain friction and engine efficiency are the same. No road is flat, but a series of varying size inclines. The gas savings on the down side do not equal what's used on the up side.