So why does my old, giant wagon, with a big motor get bad mileage?

Your engine is only 40 cubic inches larger. I'm willing to bet a Chevrolet 400 SB gets nearly the same MPG as that 350 you installed. It's not the age of the engine, or the basic architecture; an FE has a lightweight block and heads, so it's likely what was said above...that it needs a camshaft change, and a choice of better heads (as FE engines have three different intake runner sizes) and intake (I would recommend an aluminum one). Then, the timing gearset needs to be set up, and the cam degreed, to ensure no valve-to-piston clashes happen. You may want to google 390 setups, see if anything with decent power but better MPG pops up at you.

 

What oil are you using in the engine and what gear oil are you using in the differential?

 

Ak_Eric
yeah your gas mileage low, might be pricey to drive as a daily driver,
And if it helps my wife's 2010 ML350 gets around 14mpg in town and has never broken 20 on long highway trips.

but when it is all said and done you are driving a classic that very few people have and its a beautiful looking wagon!
I saw your gallery page.
enjoy the ride

 

I didn't buy this for the mileage, it's totally fine on my 4 mile commute. And I only drive it 1-2 days a week (when it's not raining), otherwise I'm on my bike. Honestly my main question on the thread was 'does this mileage sound about right for this car'. Sounds like maybe it's a bit low, but within spec (?)
I figured the new Edelbrock intake + FiTech EFI + new dual exhaust would help the mileage, but they have not. It's all good. I'm not going to dump any more $ into this motor, if I want something better i'll just buy a new one and have it dropped in. All my friends think I should convert it to electric Mainly again, just about expectations.

Oil: 10w-40 + ZDDP additive
Diff oil: I don't know: when I bought the car I took it in and had all the fluids changed (oil, tranny, coolant), and when they checked the pumpkin they said the oil in there looked totally fine. Figured if it looked remotely bad they'd try and sell me on it, but they did not.

Again, thanks for the thoughts and comments.

 

You should talk to Jairus. I think he is running a 390 is his '58 Ford wagon with a four barrel and probably a three speed trans. See what kind of mileage he is getting. Six mpg would tick me off regardless of whether it was a daily driver or nice weather driver.

 

I answered via PM.
Since the speedo head locked up... I have no idea how many miles I put on it currently. But can guess from where I go that in the city I get worse than on the highway at 55.
Probably 8 to 10 in the city and 12 on the highway. Mostly that is due to the crappy roads and short green lights in this town. We spend most of our time idling at those lights for heavens sake!
I do know that with that old 2bbl Ford carb mileage was indeed around 6.
The new and improved Edelbrock easily doubled that as long as I don't stomp on the gas at the green light.

Just baby the car, keep the tires up to max pressure and don't be fuelish !!!

 

Which additive? I should have also asked which oil you're using? Depending on which oil you use, it might give a small increase if you change to another one on the next oil change. Then again, the oil I'm thinking of is a Diesel oil; yes, it'll have more Zinc than Gas engine oil but it'll have more detergents too.

 

I used 'normal car oil (10w-40)' with this fill up + the additive, but plan to switch to diesel next time since it comes with that additive automatically.
Which specific ZDDP additive did I use? I have forgot.

 

I meant which brand, what line of oil and if it's conventional or full synthetic (sorry if I wasn't specific.) Once I knew that I was going to look up the individual oil's data sheet to compare which oil might be a little thinner if you'd like (but still within the Xw40 range.) Shell T6 5w40 might give a small boost or it might not be noticeable.

 

Oh, it's conventional, but the specifics I'm not sure of. I had my local "OilChangers" do it (which is why I supplied my own additive), and they did 'research' and came up with whatever house brand they had a match for. I have to use them since.. I live on a hill with no flat space. Not that I really enjoy doing oil changes, but it sucks that I can't at all.

But if you have any suggestion on what to use for my next change, I'll gladly hear it.

 

There are some options, depending on how thin you'd like to go; I'll list from the thinnest to the thickest. I've used all of these oils and the thinner the oil, the higher the MPGs will be.

I got around 21 with T6 0w40 and 20 with M1 5w40 and T6 5w40. Mileage went down to 18ish when I used an oil that's 15.2 at 100° C.

1: Shell T6 (Diesel) Synthetic 0w40: 75 at 40° C, 13.2° at 100° C.

About $25 - $28/Gallon. I used this once (AutoZone put it on clearance years ago,) MPG went up in the Suburban Diesel compared to the previous oil (not listed below but which was 76.9 at 40° C and 14.0 at 100° C) but this T6 0w40 will probably burn oil the most out of those listed here; its viscosity's near or at the very bottom of the Xw40 range, maybe it's better reserved for Alaska.

2: Mobil 1 Turbo Diesel Full Synthetic 5w40: 97.9 at 40° C, 14.5 at 100° C.

About $25/Gallon. I used this for a while in 2015, compared to the conventional Shell 15w40 the engine had at purchase (118 at 40° C, 15 at 100° C) this Mobil 1 oil gave a nice MPG boost.

3: Shell T6 (Diesel) Synthetic 5w40: 90 at 40° C, 14.9 at 100° C.

$20 - $25 a gallon. Very common oil but when the engine's hot it probably won't give you much of a boost over your current oil.

 

I haven't read this since the 1970's!!!

 

Didn't Ford use those electrical torque converter locks like GM did? If so, did these lockable converters really help gain milage or was this a farce?

 

Really great breakdown 101V, thanks for that! And to confirm, all of these (Since their diesel) come with the proper additives?

 

I have no idea what all those temperature numbers are that 101volts has posted. However, this info taken from Popular Mechanics is the same info I learned as a Shell Oil dealer for 35 years.

"Viscosity (a fluid's resistance to flow) is rated at 0° F (represented by the number preceding the "W" [for Winter]) and at 212° F (represented by the second number in the viscosity designation). So 10W-30 oil has less viscosity when cold and hot than does 20W-50. Motor oil thins as it heats and thickens as it cools. So, with the right additives to help it resist thinning too much, an oil can be rated for one viscosity when cold, another when hot. The more resistant it is to thinning, the higher the second number (10W-40 versus 10W-30, for example) and that's good. Within reason, thicker oil generally seals better and maintains a better film of lubrication between moving parts.

At the low-temperature end, oil has to be resistant to thickening so that it flows more easily to all the moving parts in your engine. Also, if the oil is too thick the engine requires more energy to turn the crankshaft, which is partly submerged in a bath of oil. Excessive thickness can make it harder to start the engine, which reduces fuel economy. A 5W oil is typically what's recommended for winter use. However, synthetic oils can be formulated to flow even more easily when cold, so they are able to pass tests that meet the 0W rating. "

The reason the additive is required is because of the higher spring rates needed for flat tappet cams. If it's not present, then the lobes of the cam will wear. This all changed with the advent of roller lifters and the additive was no longer required. I don't know if modern diesel engines have roller tappets or not, but if they do the oil used in them no longer requires the zinc additive. You cannot assume that just because an oil is rated for diesels that it can be used in your engine.