'38 Special gas mileage

[jeff]

I have a '38-48 (2 door Special) driver. Everything has been pretty much worked over, and it runs great. My question, what kind of gas mileage should I expect? I have taken a few long runs, and it looks like I am getting about 12 mpg. This was recorded on a 200 mile run with speeds of 35 - 50 mph (never more than 50!) Of course the car has the 248 cu in engine with a 4.40:1 rear.

I would guess a 6 cylinder overdrive car of this vintage might get about 20 mpg, a small eight like mine about 15 - 17, and the bigger eights around 12 - 14. Any thoughts?

Jeff

[Guest Straight eight]

I have a 47 Super with the same rear end. The owners manual states on the fuel consumption chart:

30 mph = 19.0 mpg

50 mph = 15.0 mpg

70 mph = 12.0 mpg

On a recent trip similar to yours I managed to get 18mpg with four passengers, driving economically with vacuum of at least 10 inches or more. (Another words no fast take offs, driving like you have a egg between your foot and the gas pedal, mostly country driving, very few stops and starts. I have the timing set a little more in advance than stated in the manual, by approxmately 2-3 degrees. Gas octane is much higher than when the car was new. <img src="http://forums.aaca.org/images/graemlins/laugh.gif" alt="" />

If you don't have a shop manual, please try to get one. They are full of valuable tuning information.

Oh by the way, I had been driving with my tappets set too tight,(didn't follow the manual). Following manual procedure increased the mileage from 14 mpg.

[Guest Ron3660]

My 1936 / 60 gets about 8 mpg at 55-70 mph. I'm running a compound intake and Isky regroung my cam to a 3/4 race. That damned coupe will pass anything but a gas station.

[neil morse]

I'm resurrecting this old thread because I'm wondering about the gas mileage I'm getting with my '41 Super sedan, which I've only had for about six months.  My gas gauge is not working (soon to be fixed, I hope), so I have been keeping track of how much gas I put in and checking it against the odometer to try to get an idea of how often I need to fill it up.  Well ... yesterday I ran out of gas because I had been estimating based on some periods of mixed city and highway driving, and figured I was averaging around 10 mpg.  During the past month or so I used the car exclusively for short trips around town, and I was surprised to find I had run the 18 gallon tank dry in just over 100 miles!  That's about 6 mpg, which seems awfully low.  The engine runs great, but I'm wondering whether there's anything that I could (or should) do to get better mileage.  (The car is running the original 248 c.i. engine with compound carburetion.)  Any suggestions?

[MCHinson]

Neil,

 

I have no experience with compound carburetion but from my personal experience with my 1937 Century, there are two things that can significantly reduce your fuel mileage... carburetor(s) running too rich, and poor ignition spark. My carburetor was running way too rich when I got the car. I had it rebuilt and I had a good running car but when I discovered that the ignition system needed significant work to get it operating like it should have, the car became much more powerful and also got much better fuel economy.

[Mark Shaw]

Jeff,

    I have the same car as yours and I get the same 12 mpg from the stock set up.

[DonMicheletti]

Neil,

My '38 Roadmaster gets 11.3 mpg overall. Yours should do some better. Something is wrong at 8 mpg.

At least a tuneup is in order to be sure things are right.

[neil morse]

Thank you Matthew and Don.  Be careful what you recommend, Don, because you know that you're the one in my general neighborhood who I'm likely to lean on when I need help with something! 

[dibarlaw]

Another factor on the fuel mileage if you consider evaporation. Unless you are driving the car regularly and keep the tank pretty full there is more evaporation with modern fuel. Modern closed systems avoid evaporative losses. I was surprised that when I put 5 gallons in a dry tank of my 1925 Buick in December. I tried to start it and work on the engine a bit. At most it ran for only about 10 minutes, twice, before I removed the carb to rebuild. I did not get back to it until the end of January. The tank had about a 1/2 gallon left when I drained it to do other work.

 I do the same procedure as yours with my 1937-41 as I had gone through the sending unit before installing. All seemed to work well

until our trip to South Bend in 2013. Somewhere in northern Ohio it seemed that we were going a lot farther than normal and the tank gage still showed 1/4 full. When we found a gas station I put in 17 Gallons. Gage still showed 1/4 full! I still have not gotten around to pulling the tank to get at the sending unit.

 Doing mileage/fill calculations our trip from South Bend average was 16 MPG! Our trip to Brookfield at best was 14 MPG. Keeping speed below 55 mph. Then when the #8 cylinder was shut down by a hammered closed plug gap (I still need to investigate this as that cylinder is now down to 60#) more like 10 MPG. I did change out the plug for the final 135 mile leg of the trip home.

[neil morse]

Larry, you may be on to something with your point about evaporation.  The period during which my tank was emptied extended over about two months -- including a three week period when we were on a trip and the car sat idle in the garage.  I wonder how much gas was lost to evaporation during that time?  A significant amount, based on your experience.

[Guest]

A non vented gas cap would cut down somewhat on the evaporation but you would need to remember to remove it before driving.  Probably not worth the bother.

[jenz38]

Jeff,

You had think about our aircleaner ?

The old oilbath things are often clogged.

I run newer, modern ( full stainless ,washable Holley marine-) 18" Airfilter on my Compound System  (run it  with 2 identical front carbs and straight linkage ) and it only go up to 12 mpg , if i run over 55 mph.

If i stay under 55,  normaly my coupe run with 17.5 mpg ,

at a soft sportive driving style..

 

Your Points and Valve gap (i drive with .004" less than the original .016" ) are correct ?...,and your Choke-flapper are full open ,when warm ? ;-).

Exhaust too, an inside broken clogged muffler results the same problem ..less power and high consumption.

 

.. i would say, try at first a fresh Airfilter... ;)...

 

 

[jenz38]

Here a pic of mine :

 

 

 

Edited October 21, 2017 by jenz38 (see edit history)

[mcdarrunt]

My 37 Special 4dr has the same body as a 38 so wind drag should be the same. I tuned it with an Allen engine analyser which had an exhaust sniffer for dead on carb sttings as well as displaying the condition of the entire ignition system, removed the sun visor, had radial tires with 40psi, Torco lube in gear boxes, 190 degree T-stat, front end aligned with just 1/8" toe in, drivers side only wsw, and taking a tip from the air racers; a good wax job. It got 12.8 mpg at 63mph using a gps speedometer for dead on accuracy. Have not checked it since the 4.44 rear was replaced with a 4.11 rear and open drive line with overdrive trans which gives a 2.88 final in o/d. I'm certain it gets at least 15 or maybe even 16mpg going by how many miles it is between fill ups.

[Ben Bruce aka First Born]

Evan, I thought you were getting 17 mpg at one point?

 

  Ben

[mcdarrunt]

Ben,

  That was when I had the 2.73 gears behind the Turbo 350. It was such a terrible combination that I don't think I could present it as a real "driver". On completely flat roads (like around here) it did nudge the 17 mark but was impractical on any other terrain. It was ALWAYS a 2.73 so starts were sluggish---0 to 60 time was done with a calendar but now with the 4.11 rear it is peppy and with the 2.88 final in o/d it is also a cruiser. I'm ball parking the 15mpg figure since it is geared deeper in straight drive and the final drive is also slightly deeper geared. I left my Garmin at my nephews place but when he sends it back to me I'll get some good figures. If I get real curious I can have one of the young guys in the shop use that wiz-bang thing they carry in their pocket do the miles and speed for me. My phone just has buttons and a flip open lid.

[414TATA]

Neil

 

We have the same car.  I too have a bad fuel gauge which bounces empty to 1/4 so I  don't trust it.  

 

My thoughts.  Your terrain is known for it's hills.  The San Francisco area in general for it's heavy stop and go traffic.  The evaporation thought probably is some of the use but most is the area which you drive.

My area is as flat as the floor and I figure no more than 12 - 13 mpg. My normal run is 16 to 25 miles of very flat road at 50 to 55 mph with very few stops.

you probably should get more than 6 but I would think with your driving conditions 8 -10 mpg  even if well tuned.  And don't forget we can't get "real" gas here in Taxifornia

Just my H O.

Good luck

Wayne 

Flat Fresno, Ca

Edited November 16, 2017 by 414TATA
typo correct and addition (see edit history)

[neil morse]

Thanks, Wayne.  Yes, I agree that driving in San Francisco is about the worst place for good gas mileage, so that's definitely a factor.  As recounted in my "Me and My Buick" thread, I ended up taking the car down to Don's where he was kind enough to help me check it out thoroughly, and everything seemed to be in good order.  As long as it's running well, I really don't mind spending money for gas, given how little I drive the car.  I was just concerned that there might be something seriously amiss, but that does not seem to be the case.

[Larry Schramm]

All of the Buicks that I have driven prior to about 1980 got fuel economy in the 10-12 mpg range.  Even the 1963 Special wagon that I owned.  I think the best that I ever got was about 14 and that was driving it very gingerly.