plastic play balls in fuel tank
 

Can anyone out there tell me the size of the opening that the fuel pump goes into on a 88091 civic fuel tank? After testing for compatibility with gasoline I may dump in a bunch of plastic play balls to take up space in fuel tank and lighten total fuel weight without modifying the tank.

The plastic balls would float on top of the fuel. until they start to leak.
Gasoline contains about 300 different chemical components, of which many may interact with plastic. It may take time to become apparent.

I think it is a fun experiment. I expect your gas tank may make funny noises when you drive as the balls move against the top of the tank. I wonder if the balls start popping out of the filler pipe if you try to overfill the tank.

In other words... Subscribed!

I don't know the specs you are looking for. But an alternate and more easily accomplished variant on your idea might be some sort of balloon attached to a long thin plastic or metal tube. You could inflate the balloon inside the tank. If permanently attached to the tube, maybe it is a more easily reversed mod, too. Lots to think about in terms of chemistry and materials. Balls or balloons, you don't want them to break down into small bits or sludge that could get into the pump.

Also, you are increasing surface area of the gasoline. If your tank is not fully sealed, then you will lose a bit more fuel to evaporation.

If your objective is to make the tank smaller, you could add a collar to the tank side of the gasoline inlet. That way air replaces gasoline.

Why not just pump less into the tank?

I'm intrigued by this idea, but have the same question as redpoint - why not just half fill the tank?

Is it so you can still "fill the tank" for mpg calculation purposes?

I've never liked the idea of carrying more fuel than needed, and spent a fair while thinking about this.

Eventually (after many overly complicated ideas!) I came up with what I call my "remote fuel tank" basically just two 20l jerry cans that I fill up when I need more fuel. I transfer it to the car 5l at a time, and reset my trip meter when it runs out.

When I'm getting near to the end of my "tank" I drive until the miles to empty indicator hits zero and that's when reset the trip meter. By this point I've got the first 5l of the next fill up in a jerry can in the boot.

Basically I'm always driving with the fuel light on, and I think I worked it out as a 15kg equivalent saving.

Theoretically my mpg readings (pen and paper method) are less accurate, but if I do over (or under) estimate it will correct on the next tank.

Noticeable mpg gains for me (mostly stop start city driving) and I can still use the full capacity of the tank if I need to.

Final thought: supposedly putting a ping pong ball in a gas tank is a good revenge tactic - ping pong gets sucked to the fuel pump and cuts the fuel, but floats up when the engine dies causing an impossible to diagnose fueling issue. Probably an urban legend, but worth considering

Chris:turtle:

Hello sluggo1010,

Sounds like you want a smaller gas tank, that acts like the gas tank you have now. Pump clicks off when it is "full", gas gage reads "full" when it is "full, etc.

If you want to use things that float - like the play balls, if they are compatible with gas - I'd suggest some sort of screen around the fuel pump and fuel sender so they don't interfere. You might have problems with being unable to fill the tank very much at all as a ball floats up and plugs the filler, triggering the auto-shutoff on the gas station pump. In a non-repeatable fashion, as they move around when driving.

You could put in a smaller gas tank with about the same amount of labor you're looking at to put the balls in. So long as it has the same "type" of fuel level sender (resistive, capacitive, other) and is also fuel injected with similar fuel pressure/volume requirements, the donor tank's pump and sender can be adapted to your Civic.

Or, for a lot less hassle, you could buy a Scangage/Ultragage/Mpguino (whichever will work on your car), calibrate it, reset fuel tank size to whatever you want to put in at the pump, and then just put less fuel in at the pump.

If you want a more violent, cheaper, more dangerous way: take old tank out, drain and dry it and maybe purge it with something non-flammable, mark on it where the fuel level sensor is, the inlet and vent pipes that extend inside, and where the fuel pump/pickup are (so you can miss them), and make it smaller with a sledgehammer. Make sure the spot under the fuel pickup and sender stay the same depth, and the spot under the pickup is the lowest point - with no trapped low points other than that. Beware sparks and don't put a hole in it. :eek:

plastic play balls for smaller tank
 

Thanks for all the great replies.
I have considered many of the suggestions made, most of which were very good and all of which are appreciated and well intended.
Still not sure which I will choose. Bashing the tank to make it smaller is a serious contender.
At this point I have to run through my first full tank before I do anything so it is not so heavy and messy. Either that or drain the tank. Was kind of hoping to see where I was at after all my mods before revising the tank.

I will post some pics when I have authorization, still in "newbie land" for the time being.

Had a modified CRX HF a few years back that always gave me 65 MPG and only had 280,000 miles on the clock. Wish I had kept it, but daughter no drive stick.

Will you let us in on why you want to reduce the fuel tank size rather than just put less fuel in?

An 88-91 Honda Civic had an 11.9 gallon fuel tank, which is pretty small. Lets say you cut the fuel capacity in half, you'd only reduce weight by 37 pounds, and your range would be somewhere around 180 miles.

Reducing weight is great for racing, but has very little benefit to reducing fuel consumption.

weight reduction is the goal. Agreed, 37 lbs is not going to improve mileage by very much, but then again. individually, none of the changes that have been made will reduce gas consumption very much. Every little bit helps.