Alright so I've owned quite a few cars in my day. I've never run into a problem like this before though, so I'm a little confused and figured I'd post up here and see if anyone has any ideas.

I have my 1998 5th gen, right. I just bought it a few weeks ago. It says it should have a 15.9 gallon capacity gas tank according to the specs. I figured this was pretty normal. Anyways, aside from my noticeably horrible gas mileage (many issues currently working on and resolving), I started noticing something strange about my gas tank.

An example, I'm at half tank on the marker. So I fill it up to the brim at the gas station. I only put about 5 gallons in the tank. I think to myself that that is odd, since I have a 16 gallon tank. Anyways, I keep driving.... this goes on for a while. Eventually I get the gas down to the point where the light turns off. Did I mention I have really bad gas mileage? Haha... well, from nearly empty (gas light on) to completely full at the station, I only put about 10 gallons tops in my car to fill it back up to the brim.

What the heck?!?! So it is looking like I have a 10 gallon tank instead of a nearly 16. What gives? No wonder I keep thinking I have bad gas mileage. When I'm 3/4 full and I put 2.4 gallons in it and it's 100% full again I know there is a problem.

At first I thought it was the gauge. But then I thought about how I have been filling it up and I know the pumps don't lie. I'm getting fuel, so I don't think there is a blockage in the lines. Maybe the floater for the gas line level is jacked up? That's the only thing I can think of. But this one has really got me stumped. My next plan is just to keep driving until I completely run out of gas on the side of the road. Then fill it up to the brim again and see if I can get 15-16 gallons out of it.

 

Carry a can of gas and run it till it is empty, not till the gauge or light says it is, but till engine stalls for lack of gas, then fill it and see how much it takes.

If it's still only 10gal check the tank itself, although I can se no reason for anyone to switch to a smaller tank and 10gal is small, that's more like a fuel cell for a race car or a tank for a very small car, even a Civic has a 13gal tank. 94

 

Yea, that's my plan for now. I checked at the dealership today and they cross referenced every possible tank that could fit my Prelude... and there were none aside from Prelude ones. So it's unlikely that someone slapped a small Geo Metro or Civic gas tank on there somehow I still need to get underneath for a picture, but I did pull everything to check on the pump and float sending unit assembly and they were so freaking dirty and dusty that they look as if the previous owner had taken my car 4-wheeling back in 1998 and then left it to sit in a garage or something for the next 13 years. So it might be time for a new pump and float meter thingy assembly...

 

Be careful when running your car down to complete empty, you may pump up crap you dont want to and clog filter and injectors even.

 

Yea, good point. I've got a Walbro 255 on the way though, and a new fuel filter I haven't installed yet... and also will be throwing new injectors on there possibly. So I'm willing to take the risk! lol

 

Not a good idea --Running a tank completely out of gas risks frying the fuel pump.

 

That would only happen if pump was left running once tank is dry, very hard to do on a Honda/Acura, and most newer cars, as pump will stop running a few sec. after engine stalls.

Could you imagine the uproar if the pumps fried for even 10% of the people that ran out of gas, [by mistake]?

I have driven every car I have ever owned, [more then a few] till tank is dry to find out where my gas gauge is when tank is empty, and not once have I burnt out a fuel pump.
I would recommend everyone do this, fuel gauges are not that accurate and they are not all exactly the same even same MM&Y.
We had a guy last year who ran out of gas a block after his low fuel warning light came on, defective thermistor

The only pumps we have replaced, [that worked before running out of gas] where pumps that would run even if engine was not running, [pump on with ign.].

The risk of sucking up "crap" is a 1000 times more likely then burning out the pump, and that is unlikely if fuel pump filter is in good working order, even then there's still a fuel filter.

Although burning out the fuel pump is possible, it is as likely as getting a flat on all 4 tires at exactly the same time, possible but unlikely. 94

 

Neither of us can assign a probabilistic score to the risk but it does happen.

 

Well like I said, even if it burned out my pump - which I'm not too terribly concerned about now - I have a new Walbro on the way to replace it with anyways.