Gas tank just started taking 18 gallons of gas when it should be 14.8 gallon tank

E

eschneggs

Member
:
Mazda, CX-5, Touring FWD
Anyone else experience this?

No leaks, I am getting over 580 miles per tank full now. Had SUV for 10 months, this started two weeks ago. Any way my vehicle got fitted with a larger tank and it has been the vapor pressure that kept it to only 14 gallons on refills before this?

Thanks
 
eschneggs said:
Anyone else experience this?

No leaks, I am getting over 580 miles per tank full now. Had SUV for 10 months, this started two weeks ago. Any way my vehicle got fitted with a larger tank and it has been the vapor pressure that kept it to only 14 gallons on refills before this?

Thanks
Click to expand...

it is indeed possible to put 18 gallons into the tank of the CX-5. It should never be done, but it is possible.
http://www.cleanmpg.com/forums/showpost.php?p=344101&postcount=4

Fuel pumps stop filling once the tip of the nozzle gets any moisture on it. On the CX-5 (and most modern cars), in addition to the filler neck, there is another small hose that runs down to the tank. When the tank is "full" this hose returns some fuel back up to the top of the filler neck and sprays fuel onto the filler nozzle, shutting it off.

see here: part #11 the filler hose is actually two hoses:
http://www.zoomzoomnationparts.com/showAssembly.aspx?ukey_product=48706111&ukey_assembly=6230476

In your case, the hose running back up to the filler neck might be clogged, so the fuel pump does not detect your tank filling up.

TLDR:
You should get this looked at by the dealer ASAP because overfilling your tank can cause expensive problems down the line.
 
So he's getting an extra 3+ gallons into a clogged filler pipe? Sorry, I'm not buying that. And what exactly is the Cleanmpg review post saying???
 
Last edited:
paris1 said:
So he's getting an extra 3+ gallons into a clogged filler pipe? Sorry, I'm not buying that. And what exactly is the Cleanmpg review post saying???
Click to expand...

here is the relevant part of the cleanmpg post:
The first click began at just .2 gallons and I added another 4.0 on top of that so the Mazda CX-5’s actual capacity is probably closer to 18 - 18.5 gallons, not the 14.8 it is spec’ed at.
Click to expand...

Basically, if you fill the entire tank, vent pipes and filler neck, the car can hold 18+ gallons of gas.
Normally, topping the tank off so high is very difficult and time consuming because the gas pump shuts off automatically once fuel gets on the tip of the gas nozzle.
If the small hose that sprays fuel onto the tip of the nozzle once the tank if full is somehow clogged, OP would have overfilled his tank without even knowing it.

If you want to see the "small hose that sprays fuel onto the top of the nozzle" in action, next time you fill up your CX-5 pull the nozzle out of the car just a second after the auto shut-off stops and look into the filler neck, you'll see fuel getting sprayed out of the side of the filler neck.
 
piotrek91 said:
here is the relevant part of the cleanmpg post:

If you want to see the "small hose that sprays fuel onto the top of the nozzle" in action, next time you fill up your CX-5 pull the nozzle out of the car just a second after the auto shut-off stops and look into the filler neck, you'll see fuel getting sprayed out of the side of the filler neck.
Click to expand...

I've actually seen that once before and wondered, WTF!? Never saw it again, so I assumed I was imagining things. Guess I wasn't.
 
piotrek91 said:
If you want to see the "small hose that sprays fuel onto the top of the nozzle" in action, next time you fill up your CX-5 pull the nozzle out of the car just a second after the auto shut-off stops and look into the filler neck, you'll see fuel getting sprayed out of the side of the filler neck.
Click to expand...

This doesn't make a lot of sense to me.

You are saying that fuel is sprayed on the filler nozzle when the tank still has room for almost 4 more gallons of fuel. The tank is not pressurized so please explain how fuel gets lifted two feet from tank level in order to spray out near the filler orifice without a pump to do the lifting. Yes, there is a vent line but how is it pressurized?
 
If the line has suction on it, like siphoning gas from a lawn mower with a hose, or a fish tank, maybe that
is what he is referring to. Just a thought, I didn't look up how the system works.
 
eschneggs said:
Anyone else experience this?
No leaks, I am getting over 580 miles per tank full now. Had SUV for 10 months, this started two weeks ago. Any way my vehicle got fitted with a larger tank and it has been the vapor pressure that kept it to only 14 gallons on refills before this? Thanks
Click to expand...
580 / 18 = 32.2 MPG this doesn't add up to me unless you drive all 580 miles on the highway. How many times did you pump the gas within two weeks? Were you using the same gas station? The other possibility is the gas pump was not accurate which happened to me a couple of times before. One time I pumped 16.5 gallons of gas into a 15.3-gallon total capacity gas tank on a Honda CR-V at Costco. The manager told me it could be the gas station storage tank was low which caused the inaccuracy. There used to be some gas stations modifying the pump to make it pumping less gas than indicated. I don't know if this is still true or not. (uhm)
 
Eschneggs doesn't say whether he has the 2.0L or 2.5L engine or AWD or FWD. But the 2.0L engine easily returns 32.2 mpg in mixed driving. In fact, my 24,000 mile average includes every fill up since new and I'm averaging 32.4 mpg lifetime average including many miles of slow, steep back-country driving on rugged mountain roads. And I have AWD and AT. FWD would return higher MPG numbers. So I have no problem with the calculated MPG.


I do have a problem with the claim you can squeeze 18 gallons in and I'm not about to try it. Overfilling the fuel system can cause fuel to flood into the emissions equipment and cause damage or even create a fire hazard. I always stop when the auto-shutoff kicks in and I still get over 500 miles/tank on road trips. The most I've ever put in was 13.52 gallons.
 
MikeM. said:
This doesn't make a lot of sense to me.

You are saying that fuel is sprayed on the filler nozzle when the tank still has room for almost 4 more gallons of fuel. The tank is not pressurized so please explain how fuel gets lifted two feet from tank level in order to spray out near the filler orifice without a pump to do the lifting. Yes, there is a vent line but how is it pressurized?
Click to expand...

Mike,
good question.

With my very limited understanding of the inner working of EVAP systems I can't come up with a fully satisfactory answer, but there is definitely some pressure in the tank as it gets filled and fuel definitely gets pushed up thorough the vent pipe.

check out this ford patent from 1993.
http://www.google.com/patents/US5327934

a relevant quote from there:
As fuel continues to enter tank 10, tank pressure rises until it causes fuel to back up into the filler pipe 12 consequently shutting off the fuel nozzle (not shown). Thus, containing fuel vapor within the fuel tank during refueling contributes to prevention of tank overfill.
Click to expand...

There is lots of fuel vapor still in the tank when the filling stops. If one tops off the tank, or if something is wrong with the system (which is what I suspect happened to OP), it's possible to displace that vapor with fuel. if that's done, the filler neck can also be used to store extra fuel.
The vapor area combined with the filler neck is likely where the extra 4 gallons go.
obviously those 4 gallons should not be used for storing fuel, but the volume is there.

I fully agree with you that squeezing 18 gallons into a CX-5 is at the very least, harmful to the car, bad for the environment and at worst a serious fire hazard. I would also never attempt to overfill my tank in that manner.
I think that if OP's CX-5 really does take 18 gallons (which IMO is very possible) he should get his EVAP system checked by the dealer ASAP.
 
Last edited:
Here's another possibility: The gas pump is lying to you and therefore charging you more. This kind of metering fraud is very real. States are supposed to keep an eye on this, but sometimes budgets for enforcement are cut.
 
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