I'm planning a trip to Utah. I have $150 to get there. It's approximately 668 miles. I'll be pulling a ~20' enclosed trailer full of household stuff (friends moving).

The truck is a 74 w200 with a 1972 440. I have a street avenger (670) carb and K&N filter. Truck runs awesome. I just did head gaskets. All upper seals redone. New radiator, hoses, front brakes, power steering pump and hoses, new belts, etc.

My speedometer is broken and my fuel gauge is unknown accuracy.

Should I calculate 10mpgs to be safe?

Pulling a trailer... I'd say 8 mpg to be safe.

Fixed.

On a serious note, single digits definitely. Have you ever pulled anything with the truck before? How a truck runs unloaded can be a huge difference from when it's loaded.

No I haven't pulled anything this heavy. Only a 5x8 landscape trailer.

I had initially calculated 6mpg. But that means I'll need $300 to get there.

But I do believe it gets better gas mileage than I initially thought. With the gas gauge broken, and speedo broken, I pumped 16 gallons to go roughly 70 miles (figuring on 6 mpg). But I made it there, and back, and did a tremendous amount of driving before pumping gas again. I pumped according to 6mpg, and drove. When I pulled the fuel level sending unit out to swap it, I though my tank was empty. I was afraid to run it for fear of running out. But to my surprise, it was half full. Unloaded, the truck seems to get about 11-12. I'm going to fill up a gas can. Drive the truck until empty, and fill from the gas can. Then run it dry again.

Or possibly filling up, then driving for a distance, and pumping at the same pump. Hopefully it clicks off at the same point both times.

Pumped 13 gallons. Got just over half a tank (started at ~1/8th). Went on a 60 mile round trip and still have just under half. It'll still touching half. If the truck leans right, she goes up to 3/4. 60 miles round trip was all freeway driving at 55-60mph. With short bursts here and there (passing).

I'd venture to say this truck is getting probably 14 or so unloaded. So 10 loaded should be attainable.

Keep in mind the speed you drive is going to have a huge affect. Your truck at 55 versus your truck at 75 is a huge difference. If you kept it at 55 I bet you can get the 10mpg. At 75, no way!

-Jon

Try inputting your trips and fuel ups on fuelly.com to get a real world estimate of how your truck is performing. I did this with my daily driver and found out that my MPG gauge projects my car gets 1 mpg more than what I'm filling at the pump. I'm assuming your odometer is working.

Pulling a 20' enclosed? I'd calculate at 6mpg and be happy if you exceed that. I think 8 is realistic, 10 is pushing it IMO.

My 77 w300 with 360 gets 8 empty. Runs out of rpm by 60 MPH.

I think you're initial estimate was righjht on the money for pulling a trailer.

Make your friend pay for the gas.

What gears does it have? 3.54 gears 10-12 mpg is realistic. Not so much with 4.10 gears.

Not sure what gears. I looked for a tag when I topped off differential lube, but didn't find anything.

I'm going to guess 410's because this thing can climb hills idling in granny in 4lo. It is a stump puller!

As far as running out of RPM's, I can keep up with cars going 80+ and still have pedal. Only thing stopping me from driving that fast is that a couple tires are questionable for high speed driving. They're sun cracked. I don't think they'll cause me issue at 55mph, but that's tops anyway. I rarely go past 60 unless I'm passing.

This one!
I've had a few big block Dodge trucks. 7-8 mpg if your working them (which pulling an enclosed trailer will be doing), and hope for a tail wind! If your pulling a loaded box, that's taller & wider then the truck, into the wind, its going to suck down even more gas.

If your tires are sun checked, I suggest you change them before you leave! Trying to buy Dodge 16.5 tires on the road won't be any fun. Driving 600+ miles on sun checked tires is asking for trouble. Sun checked tires around town might work out OK, but for hours at a time on the highway? No way!
Just my opinion. Been there, done that. Gene

If you have 16.5" wheels, before you buy another 16.5 tire, look at replacement costs vs a 16 or 17 wheel and tire package.

The 16.5 is an oddball size and the selection is poor, the tires you buy may be five years old, and the cost is probably going to be high.

R.

Just got back from the trip. 7.6mpg up, 14mpg down.

Towing at 55mph, truck was a dog. Hated hills. But if I hit hills at 76-80, she pulled no problem. I burned 3 quarts of oil on the trip up. Only 2 quarts down.

Had no real issues. Brake lining on driver side started separating, so I warrantied them out. Did some exploring, and even found a pick and pull. There was a 76(?) so I grabbed the passenger front side marker.

Truck rode like a TANK!!!! But it was great hahaha

So you averaged 10.8 mpg. Not bad. The using 5 quarts of oil to go 668 miles isn't too good though.

The oil consumption could be caused by weak valve stem seals (assuming no significant leaks). If the seals are shot and maybe the valves to guide clearance a bit high, it can loose a lot of oil... I know by experience. Also check plugs for a whitish deposit from the oil burning. A set of valve stem seals may help.

Also, if the truck does not climb well at 55 and seems happy at 75-80, I would guess it has a 3.54 rear. 4.10's and more or less standard size tires and the engine would be singing at 75-80.

Valve stem seals were done when I did head gaskets.

I did notice the oil pan rail was really wet. I couldn't tell where it was coming from, but the sides of the block were/are dry. When I had the flywheel off doing the clutch, the rear main didn't look like it was leaking, but may have started on the trip(?) I may pull the oil pan and replace the gasket for good cause, plus I can inspect bearings at the same time.

Forgot to mention, tires I'm running are 33x12.50x16.5's. Truck loves doing 75-80. That's it's comfortable speed, and there is plenty of pedal left.

I agree, that's good. My D100 2wd 400/4speed gets 9 mpg unloaded.

I would replace the intake bathtub gasket. I've had more the one big block suck oil up into the intake runners from under that tin gasket, and I've had more the one leak at any one, or all 4 corners at the head to block corners when driving highway speeds or turning higher rpms. Gene

Valley pan gaskets are new. I used fiber gaskets on either side of the valley pan. Only thing I can think of is one bolt wouldn't torque to spec. It torqued to 25ftlbs but would not torque above that. Hmm

I wouldn't use gaskets with the tin valley pan. It's meant to be used solo.

How do you seal the mating faces? Silicone?

Yes, the blue stuff, on both sides of the head surface on the tin plate and on the block and corners of the block/head. Gene

I only use silicone under the front and real valley pan hold downs. Under the intake flanges I just mask them off and spray them with the copper gasket spray.