Two fuel tanks, lots of confusion

by Linda Anfuso

Question: Our dinosaur 1978 motorhome has 2 fuel tanks. the larger one for the engine seems to pump into the smaller one sometimes. (There is a sudden drop on the fuel gauge of about a quarter of the tank) If we leave the engine running while filling the big tank, fuel comes pouring out of the little tank. why?

We were advised by the previous owner to run the engine off the smaller (generator) tank for about an hour when both tanks are full, then switch over. Why?

Sometimes going up and down hills we can smell gasoline if we are using the small tank. It seems to go away when we switch to the big tank. Why? ?

Answer: You did not mention the type of make or model of your RV so we can only speculate.

The first advice we have for you is to never leave the engine running while refueling. This is a big time no no. It strikes us as an unusual situation which might also be dangerous, especially if you meant to say gas fumes come out of the small tank.

The next thing that comes to mind is that the big tank may have lost a baffle or a check valve has stuck open that would prevent gasoline from
sloshing from one tank to the other.

We suggest that you ask the following questions. Find out if the secondary tank was a factory option or was it an add-on. If it was a factory option then you might get some answers from the manufacturer concerning your questions. If the secondary tank was installed by someone else, then there may not be an easy solution and the installation may have been done incorrectly.

Once you know the answer to the tank question we strongly feel that you need to take the RV to a qualified repair center. Do not mess around with a dangerous situation.

Comments for Two fuel tanks, lots of confusion

Aug 22, 2014 More detail re fuel tanks
by: Linda

Hi there! Thank you for your very prompt reply. The RV is a 1978 Georgie Boy Cruise Air, built on a Chevy Chassis, with a new Chevy 454 Big Block engine that we put in ourselves because the old one had a cracked head, and other irreparable issues.

From the specs that came with the motorhome the two tank arrangement seems to be part of the original build. The smaller tank feeds the generator and the larger one the engine. There is a dashboard switch to change them over.

According to the specs, one tank has a feeder pipe to the second tank so you never run the generator so much that you totally deplete the engine fuel.

What concerns me is that the pump pumps fuel from the engine tank into the gennie tank, so we see a sudden drop off about a quarter of a tank when we’ve only been running it for about fifteen minutes or so, and the smaller tank then leaks that fuel if it was full to start with. Hence the need to run off the smaller tank for an hour or so after filing, to make room for the incoming fuel as we drive.

The former owner simply says it’s how it was made.

I don’t like the idea of any fuel leaking from anywhere. It leaks from the fuel cap. They appear to be original to the vehicle, but being so old, if they ever had a spring loaded inner seal it has long gone. We’re having difficulty finding new ones, and I don’t know if they ever were spring loaded. Some systems depend on a breather cap to prevent vapor lock, this may be one of them.

We have become accustomed to this situation, have learned to never fill while running the engine, (station owners get a mite tetchy when you dump gallons of fuel on their property….) and to run off the smaller tank for an hour or so when both are full, but the smell of an obvious copious gas leak is alarming when we don’t.

I am wondering if other dinosaur owners understand how this works.



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