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Gas Mileage 1940 Super 8


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After 1,400 miles of driving my 1940 Super 8 with overdrive, I realized roughly 10-11 mpg. Thinking something wrong, I crawled under the car and noticed the bottom of the fuel pump was saturated, but not heavily dripping. I tightened each of the several screws about 1/4 turn. Another 220 miles and my mileage "jumped" to 12mpg. In the beginning, I was driving 65-75mph for a while, so I slowed down to see if that would help. At 55-60mph hardly any change. The last 220 miles were done at 55-60mph.

If my mileage is the same at 55-60 as it is at 75, it's a no-brainer how fast I'm going to be driving.

Any suggestions as to where all he fuel is going. I've been told that I should be getting better than 15, even close or better than 18mpg. My dad's car gets more than 12 (same body style) and he doesn't have overdrive.

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First question you should ask yourself is what is the internal condition of the engine, for example what the compression reading? You need to have all cylinders at or near 105 psi for good mileage. Secondly what's the state of tune-up (plugs, points, ignition timing, etc.). Other things to consider is tire inflation pressure, carburetor float level and choke (wide open, I hope, when hot), and you might even consider checking the main jet and metering rod sizes. And of course lastly, your driving habits.

My experience with 356 engines is that I got about 18 mpg back in the days of good old leaded gasoline. More recently with MTBE gas, about 17. Most people I know driving 356 cars with OD now get about 15 with the ethanol gas.

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I've not yet checked my compession. Plugs are relatively new, wires are brand new. Don't know the age of the points, but the engine's temperature is probably a little warmer than it should be, so maybe I need to look into changing them and adjust the timing. Carburetor is freshly overhauled and restored.

Also, I suppose I might be dragging a brake or two, but wouldn't I have noticed smoke (or fire) if so. Is it possible to have a dragging brake without any physical signs? I noticed that unless I was on a really steap hill, the car tended to slow down when in neutral going down long, Pennsylvania mountain roads (turnpike driving).

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If the compression isn't up to snuff, you'll never get decent gas mileage so that should be a priority on your list. Do it with a warm engine, all plugs removed, throttle and choke valves propped open. At least 3 compression strokes or until the gauge stops rising will give the correct reading.

If you don't know the condition of the points and condenser, best to just change them now.

After a short drive, just reach under and feel the brake drums. If you have a dragging brake, that drum will be much hotter than the others, maybe even too hot to touch.

Driving at a continuous 75 mph is really flogging an old car of this vintage. You probably should expect gas mileage to drop 35% or more between 50 and 75.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Owen_Dyneto</div><div class="ubbcode-body">Driving at a continuous 75 mph is really flogging an old car of this vintage. You probably should expect gas mileage to drop 35% or more between 50 and 75. </div></div>

Thanks for the tips. Yes, you're right, 75 for long periods is not good. It is my plan to drive the car at 65mph most of the time. Going 75 is easy for the car, and comes in handy when getting around traffic, then settling back in at around 65mph.

I'll look into getting the compression checked, changing the points/condensor, and checking the vacuum advance (as well as feeling the brakes), then get back to you if there's improvement.

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I would not be too worried about gas consumption, considering that we do not drive our Packards as everyday cars. I recently went 1500 miles in my 53, Clipper Deluxe at 70 mph and got 13.5 mpg, I also regularly get 17 mpg from my 1938 Packard Six with overdrive at 70 mph. My 35 Super gets 15 mpg at 55 mph with two bikes on a trailer attached. My 1946 Daimler DE27 has never got better than 10mpg under any circumstances. My son's 1993 Ford 4 litre OHC Fairmont gets 20 mpg at 65 mph on our freeways with cruise control. Some of my English friends chide me on my choice of Packards, because of their size and lack of economy, but be aware that most of the English and European cars were even worse gas guzzlers. The 56 Clipper road test in England amazed the English at how fuel efficient the Packard was and it is a shining light. Read the test which is amongst the listings. Best regards peter Toet

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Peter

It's not the gas consumption I'm "worred" about, it's knowing that there's something wrong with it that bothers me. The engineer in me likes to tinker with mechanical things and make them work as designed. I think of it as a puzzle and relish and get excited about restoring the smallest of things. I know the car is supposed to be getting somewhere around 18mpg with overdrive, so I want to find out what's wrong with it. And with my slight overheating problem, the two could be related. Fixing one may fix both.

I felt my rear brakes this morning after arriving at work. They were cool. Check that one off the list.

The car has had a recent valve job, so I doubt that the head gasket is the problem (not out of the question, though, I guess). We have looked at the points and they appeared to be okay, but it wouldn't hurt to replace them.

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My 1950 288 cu in engine had a couple of bad valves that resulted in poor compression in those cylinders. So I sprang for a valve job, which was rather costly because the head had never been off the engine and was the devil to remove.

The car ran like a top (and gas mileage improved to more than 15 MPG on the highway) for several months. Then I started to smell fumes coming from the engine. Inspection revealed they were coming from the road draft tube, which is part of the oil cooling system. Turned out the rings were now shot in two cylinders, causing blow-by. Basically, by tightening up the pressure on the top end, I over stressed the bottom end. So now I am back to getting the same gas mileage I was before the valve job AND I am looking at a major engine rebuild that will replace bearings, pistons, rings, etc. My advice: if it ain't terribly broke, don't fix it.

All the best,

Mark in Alaska

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Yes you should be getting better than 12 mpg with an overdrive equipped. What carby are you running on it, if it is the original Stromberg AAV-26, it has a power valve fitted. The power valve is usually set to operate under low vacuum conditions such as acceleration OR MAY BE OPERATING BECAUSE YOU ARE IN OVERDRIVE AND LOADING UP THE ENGINE SLIGHTLY MORE. It is just a thought as it used to happen on my 38 SIX with a Chandler Groves Carby. Do you have a spare carby or a friend with the same carby, so that you could check if it is the carby or some other function which is causing the excessive consumption. I have used an exhaust gas analyser in the past to check n carby operation and they are a useful diagnostic tool. If it is running a bit hot, you can purchase a small infa red temp gauge for about $30, with which you can check your radiator tube temps from the front of the car. The hot ones are carrying water, the cooler ones are blocked. Remember that only the top two or three inches of the tube blocks up. The same gauge can be pointed at the front and rear of the read and block to determine the temps. You should be running about 140 -160 at the front and about 170-180 at the rear with the hand throttle set to about 1,500 rpm. Something to think about. Peter Toet

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CaptainBristol</div><div class="ubbcode-body">Basically, by tightening up the pressure on the top end, I over stressed the bottom end.Mark in Alaska </div></div>

Uggggh. I hope that's not what I'm experiencing. My valve job entailed replacing one bent valve. The car runs as smooth as can be, but now you've got me worried.

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West, if it starts and runs, does not foul spark plugs, and/or does not require 4 quarts of oil a day killing the local mosquitoe population, I'd say don't worry about it. Gas is cheap, if you're not burning it every day! smile.gif

Have fun, drive the beast!!! cool.gif

Wayne

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"The Beast," hmmmmm. A possible nickname, perhaps? shocked.giflaugh.gifgrin.gifsick.gif

Actually, I HAVE been driving it every day. I figure if I get caught (since it has collector plates), I'll explain that I've been fixin' up "The Beast" for the last three years and I'm out testing each little "fix" I make. Don't know if that'll work, but it's worth a try.

"Officer, I'm doing a fuel mileage test. Bear with me, please. With only 20 gallons in the tank, it shouldn't take more than 200 miles before I have the information I need." cool.gif

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West, "the Beast" would be a totally inappropriate nickname for such an elegant automobile!

I have Historic Vehicle plates on my Packard also and the Highway Traffic Act allows the car to be driven for road testing. Needless to say it get lots of testing! smile.gif

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Dave

We're on the same page as far as "testing" is concerned. It seems like I'm constantly testing the tires to "see if they still go 'round in circles."

I was razzing Wayne cuz I don't like to give my cars nicknames (see the special post up in the General section). I call it "The Packard." Sometimes my wife calls it "Patty Packard," but stops immediately after I give her a few wet-noodle thwaps upside the head.

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  • 2 weeks later...

Haven't done any compression testing, but I really don't think that's the problem. I have been doing some thinking, though...

1. Timing may be a little bit off, although it really runs smoothly. Wouldn't it run kind of rough if the timing were off?

2. My tires are oversized 7:50-16 rather than 7:00-16, causing an odometer error, but that wouldn't make a difference of more than about a 1/2 mile per gallon (mathematically).

3. New gas doesn't give as good mileage as the old.

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