MPG increasing as gas is cleaning carb?

[Cubey]

I drove my van to town and home again (about 40 miles round trip) and I could swear the gas gauge went down less than it did a week ago for about the same miles driven. I might be wrong. My gas gauge it's 100% working right, may be a faulty sender but they're rare and NOS so a "new" one might not be much good either. As it is, I had to rebuild it (new fuel sock, brass float, sanded off the surface rust) as it was in awful shape but still serviceable.

When in the "full" position (during testing) it showed 3/4 full on the gauge. I didn't know about testing resistance at that time so I didn't do any such tests. I will have to after filling up the tank since i don't want to remove the sender again right now.

Anyhow... I wonder if my mpg is increasing slowly due to driving it. The carburetor may be a bit gunky from sitting so much and is slowly being cleaned out by the gas being run through it. When I got the van, it had the wrong air filter in it, causing no filtration at all (it was too short for the taller round housing) so that could have aided in a gunky carburetor depending how much it was driven that way. I promptly installed a new Wix filter when I discovered this. Thankfully this part of the country isn't extremely dusty like out in the desert.

I am mostly putting regular grade Shell in it from the same station every time. But there has been a few times like last week I didn't, I got Valero. One time I got RaceWay. Other times EZ Mart. Just depends on what station is easy in and out along the way regardless of the price. I haven't put any additives in the fuel up to now.

I put $16 in before I came home last week and drove about maybe 4-5 miles extra than today after getting gas.

I put in $15 today and the gauge is up considerably higher than it was when I got home last week after putting in $16. Either I'm just using less fuel than I think to begin with, or it's slowly getting better mpg. Considering I was a little less soft on the gas pedal on the highway today, it may very well be getting 1 mpg better.

I wish the fuel gauge worked 100% right. Figuring 10mpg is safe enough which seems about the average it's getting. With a 36 gallon tank, I can drive about 275-300 miles before refueling without the risk of running out. I will be keeping a 5 gallon can of gas on my trailer for an emergency though... heh. Just dump it in the van at a refuel stop and refill the can so it stays fresh.

 

[RiceCake]

Your MPG testing method is so riddled with variables you'll never be able to figure out what the truth is.

Is it possible a gummy carb will start working better after its been run for awhile? Absolutely.

 

[Vikas]

He is not measuring mpg, he is measuring how many dollars he needs per time period. There is nothing wrong with that method

 

[Cubey]

I'm roughly measuring gallons. $15-16 adds 4 over gallons based on the cost around here. If it uses about 4 gallons at 10 mpg... 40 miles.

Putting $1 less fuel today rendered me with more gas on the gauge when I got home than loading $16 the other day. Even factoring in the extra miles driven the other day which would have consumed the extra $1 worth if not a bit more.

$1 of gas at about $3.50/gal only gives about 3 miles at 10 mpg. ($0.35 a mile x 3 miles = $1.05)

I need to start actually writing the miles down at every fuel stop which I did today (when I got home) in a small notepad I can keep in one of the the doghouse storage compartments. I wrote down a close odometer reading of what it would have been at the gas station based on Google maps mileage.

From now on, I will write down the odometer reading before adding fuel. The reason I don't just fill it up is:

1) the cost
2) It will sit in the bank for months before it all gets used so why bother?

For some odd reason, Dodge didn't put a trip odometer on the gauge in these vans in 1978.

 

[Clevy]

It's tough to measure accurate consumption just off the gauge. To accurately measure consumption you need to fill it right up,then drive,noting miles driven. Then at the next fill up divide mileage by fuel added to get an accurate figure.
But yes the engine may be getting better mileage now that its getting regular usage.
I suggest adding a tc-w3 2 stroke oil at a ratio of 1 ounce per 5 gallons of fuel. The oil will help keep all the rubber seals in the carb supple and prevent the ethanol from drying them out. Tc-w3 also has detergents which will keep the fuel system clean as well. I've been using it for years in everything I own that burns gas without a single fuel related issue.

 

[Cubey]

Yes, I have been told that suggestion on the forum. Where can you get it besides WM? Any auto parts store? Marine stores?

 

[Clevy]

Originally Posted By: Cubey
Yes, I have been told that suggestion on the forum. Where can you get it besides WM? Any auto parts store? Marine stores?

Anywhere you can buy auto parts or oil. In the winter I use the snowmobile tc-w3 and in the summer I use the marine version.
It's not that important to buy a name brand tc-w3. The spec itself lends to the finished product being decent no matter the manufacturer. I've been using the castrol stuff because it was on sale last time I bought some.

 

[Cubey]

My first scooter was a lil 40cc 2 cyle that required premixing and I ran redline racing oil in it, when i could get it out in CA. Moved out to AR and couldn't find it.. had to run whatever name brand I could find. I used quik silver marine oil it too.

I had a gallon jug of it cheap stuff from Walmart I bought many years ago and never cracked the seal on.. but I gave it to a friend when he bought a moped from me last year (which he's letting rust an ruin in his yard.. despite it being his only motorized form of transportation) since it needed 2 cycle oil and he's always broke due to his living arrangement at his mom's place. (Long story.)

Guess I'll have to find a new cheap jug of it someplace. Maybe O'Reilly will some in their store brand.

 

[SuperDave456]

+1 on some type of fuel system cleaner.

Carbs are more cantankerous with old or bad fuel. No computers to do the math for them.

 

[spk2000]

If you let it idle or warm up to thaw out longer that could be offsetting the difference too.

 

[The_Jeff]

I don't think it's your MPG getting better. More likely you're cleaning off your fuel sender varistor. "They" say a bad batch of Shell fuel in Florida scrweed up some senders a while back, it was sulfur or something shorting them out. Techron FI cleaner worked to clean some of them.

You need to top off the tank and drive to figure MPG, then top it off again. But I'm confident just driving is going to be good for this van.