Is it possible that fuel siphoned from the back tank to the front one?

[72-d24]

Is this even possible? Here's the scenario:

Background:

   
• The generator only runs off the back tank.
• Back tank had bad fuel in it. We emptied it and replaced a glass cased fuel filter (I don't know what these are called. They came with the rig and are edelbrock, as is the carb and intake) at the genny and ran it fine off the back tank.
• Rarely ran the engine off back tank, but did some.
• Front tank was cleaned and coated a few years back (according to maintenance records and receipts). Fuel from it seems fine.
• Never could find the in line fuel filter to the engine. Installed a glass cased (extra one that came with the rig) one near the carb.
• Front gas gauge doesn't work, rear did.

We were 200 Miles away from home. We had been getting horrid gas mileage (3.8-4.5...yuck!). Did some things to address that (changed cap and rotor, adjusted choke, and there was actually a fuel leak...scary) and then we hit some of the biggest hills in the trip so far. We just kept feeding the front tank based on a dollar per mile average and should have been close to E when we reached this location 200 miles from home. We planned to stay in the area for a few days, boondocking and checking out local attractions, so we filled up the rear tank and ignored the front, thinking that we needed the genny (I work online and have to be able to charge my computer) and that we could run the engine off the back to get to a gas station should the front run out (we didn't have any idea how much was in the front but it should have been very little). After filling up, we should have had almost a full tank in the back.

One morning, the front tank did seem to run out of gas, but when we switched to the rear, the performance didn't improve greatly; it still seemed to be out of gas. It was hesitating when going from idle to low speeds and would threaten to die (and actually die) in parking lots unless I gave it plenty of gas. We finally got to the spot we expected to stay for the night and decided to walk for gas for the front tank. Putting that small amount of gas (2 gallons) in the front tank and switching to that didn't seem to help the situation. We started to realize that we were having a fuel delivery issue, which means that we may not have been out of gas when we thought we were (but we hadn't added any fuel to that tank in a long time and it should have been close to E).

We needed to run the genny, but it wouldn't start. We walked for more gas for it and it started right up, so somehow the tank that we just filled didn't even have enough gas to run the genny???

While trying to figure out what was going wrong with the rig (the engine and the gas tank issues), we drove around the area for several days driving off the front tank, which should have had very minimal gas in it according to mileage and what we had put in it. The rear tank should have been close to three quarters or even full, but its gauge was reading 1/4 (or something like that)! We went to fill up the front tank and it only took 5 gallons (?!?). I tried to put some in the rear and stopped pumping at 10 gallons (it should have taken maybe 4, and that would have been a lot). This made me think that our whole problem with the engine had to do with venting the tanks because it seemed like air must be keeping the front tank from receiving fuel. I was worried about putting fuel in the rear tank because I didn't know where it was going. We couldn't find a leak anywhere. I wanted to put fuel in the front to try out our fixes and get headed home. 

We finally located the fuel filter (tucked behind the front bumper and frame) and replaced that. Also replaced the cartridge in the glass cased filter we put by the carb. We also had a vacuum leak that we finally found in the line between the vacuum advance and the carb. We replaced several vacuum plugs and hoses while trying to find that leak. All this took us several days to figure out as I am a mechanically inclined woman but nothing like a mechanic.

After all that, we still didn't seem to be getting enough gas to the carb. My cousin (a mechanic) had told me that the mystery "self destruct" (my sons' label for it) switch on the dash was actually an electronic fuel pump. I looked at the records for the rig and the PO did have an electric fuel pump and a switch installed to allow the rig to start quickly after sitting for a while. I flipped that switch, and there was gas at the carb, so I guess we need to replace the mechanical fuel pump. We drove the 200 miles home off the electric fuel pump with no further problems with the engine (we did do some things to clean the carb a bit also).

However, we still had the issue of the front tank not accepting much fuel and the rear one going through fuel at an alarming rate. For the first part of the trip back, I stopped at every town for fuel (about every 37 miles), but it only took a few gallons each time. It took about the same amount of gas each time, which had us averaging about 5.9 MPG if the tank was actually full (but it really couldn't possibly be). The things we did should have given us increased fuel mileage, so 5.9 seems in the right range. I finally stopped topping off the tank every 35 miles or so, and we made it home (over 100 miles since last fuel up) with no problems. I have not put fuel in again.

Somehow, my main tank does appear to have been close to full when it should have been empty and my rear tank looses a considerable amount of fuel whenever I put gas into it.

Is it possible...has anyone ever heard of...could it be that the fuel we were putting into the rear tank was siphoning into the front one?

That is the only way I can explain it, but I don't even know if that is possible. If so, Any suggestions on fixing the issue?

As a side note, we did run the generator while driving right before the real issues began. Could that be related to a breakdown in that valve between the tanks?

[DaveVA78Chieftain]

Is it possible your fuel select valve is not shifting between tanks properly?  Most likely located on the passenger frame rail in the area of the muffler/transmission.

Dave

[72-d24]

Thanks, Dave! I'll look for the valve there.


This site was a major key in helping us figure out everything going on with the rig so far. From searching around and reading up here I learned that our rig requires vented fuel caps, which is what we have, I guess. I also learned where to look for the fuel filter, it just wasn't where it was supposed to be. By reading through several threads, I was able to rule out vapor-lock (I hope that's the right term), and the "loosing power under a load" thread is what prompted us to take the day to switch out our cap and rotor, which had us walking, then driving all over a strange town to find just the right parts, which we were able to figure out by researching on here (I have that parts list page bookmarked).


From reading here I also became more and more convinced that something had to be going wrong to cause my 4 MPG average. The PO's amazing TLC and upgrades that includes Gear Vendors, new intake and carbs, something done to the headers (can't remember what he had done to them at the moment), and electronic ignition should equate to great MPG, so I have to honor him by figuring this thing out. Well, and I just need the better gas mileage to be able to afford all the travels we have planned in this thing. We are planning to head south at the beginning of the year, so I want to figure things out while at home base for a stretch.


Has no one else ever filled one tank and had all the gas seem to move to the other tank? Does that just sound crazy?


I want to just replace that valve and hope that is the problem, but I would like to know in advance that I am not crazy for thinking that way. I am sure the valve is inexpensive and easy enough to replace; that's not the problem. My concern is that, if no one has ever heard of this before or if no one else thinks it is even possible, then the only other explanation could be a massive leak in that rear tank (which means my cheep fix could cost me a pretty penny in lost gas), and something hindering my front tank from receiving fuel (although, the test of driving over 100 miles without adding more gas does show that the tank that should be empty does somehow have more in it than the few drops we are able to squeeze into it at each stop).


In reflection, though, while I am not thrilled with loosing 3/4 of a tank or more in the rear tank, who's going to complain about traveling a couple hundred miles over the Cascades while basically on E, right? I challenge anyone to top that MPG. :)rotflmao W%

[legomybago]

Is it possible...has anyone ever heard of...could it be that the fuel we were putting into the rear tank was siphoning into the front one?

This is entirely possible if a PO put in a fuel cross over line between the tanks. The line would come out of the bottom of both tanks and connect the two. I highly dought someone did this, but you never know with these old rigs

[gpw9552]

IF there is a return line from the fuel pump (like the Chevy P30 with a 454) it could be something as simple as the tank return lines connected to the wrong ports.
Look for the simple things first.

[72-d24]

Thanks for the ideas of what could be happening, guys! Those ideas are what I am hoping to hear. 

My son was all over under there when we were looking for the fuel filter and looking to see if we had a plugged vent tube. There is only one line going to each tank and they are connected at the valve. No return line and no cross-over line. We will get under there again shortly and double check.

I had heard that improper venting (because of bugs or something plugging the vent tube) is the main reason a tank wont accept fuel. At first, We were worried that the reason we couldn't fill the front tank and the reason we weren't getting fuel at the carb was because the tanks weren't venting properly. After looking for these issues and finding no tubes, and after confirming on this site that our tanks vent through the caps, whenever we parked, we kept the gas caps open but still on and locked (if that makes sense) in an effort to vent the tanks when possible.

Until I drove it about three times farther than I should have been able to on the amount of gas that should have been in the tank, I was still convinced that there was only a few gallons in there and that something was keeping the tank from accepting any more gas. Now, I think it has been full ever since shortly after we switched to the back tank when we thought the front one was out of gas.

We knew we needed to replace the fuel filter and my thinking is that it had become too blocked to allow fuel to flow properly; the fuel that came out of it when we took it off was awful looking. That blocked fuel filter is what I now think caused our lack of fuel at the carb, and I believe that the mechanical fuel pump's struggle to pull fuel past the blockage is what compromised it and caused it to fail (I don't know this; it is just what I figure was going on). We had been trying to drive off the back tank for about 30 miles before we first realized that the front tank wasn't accepting gas and that the rear tank was mysteriously close to empty (although it should have been full). Originally, I thought it was a vent issue and that the rear tank had a massive leak. We never found a leak, never confirmed a venting issue, and we were never again able to put more than 2-5 gallons of gas in the front tank at a time (I suspect that we could now, but I wont be attempting to get gas until this weekend at the earliest).

I am wondering if it is possible that, when the fuel pump was trying to pull from the rear tank, the fuel couldn't get past the blocked fuel filter and it diverted into the front tank through the valve that switches between tanks. Is that possible? It makes sense in my head, but I am not convinced as I am no expert on these things.

One more thing: after the tanks ended up with the wrong fuel levels (the full one empty and the empty one full), I began hearing a faint thud from the back of the coach when I take my foot off the gas. It doesn't happen every time, and I am not sure that it wasn't happening before.

Also, we had been on the road for over 1200 miles and for several weeks before this all happened. Until this, we had gotten horrid gas mileage and she was sluggish on hills, but no other real issues that I can think of.

Also, we did put Sea Foam in the rear tank just before all this happened.

[Wantawinnie]

Where in the fuel line is the electric pump located? They are usually better "pusher" pumps than "pullers". Just wondering if that was somehow used to fill one tank from the other like a transfer tank. I contemplated that to get a larger travel distance. If it was never on when the issue first happened then it likely wouldn't be the problem.

The other is if there is a return line that was mentioned by gpw9552. That will bleed off unused fuel and send it back to the tank. If there is only one line it would fill whatever tank that it was run to regardless of the tank being pulled from.

Both of my 73 vintage Winnies had a line from the rear tank and one from the side tank that connected to a transfer valve on the PS inside frame rail. From the valve it went forward to the fuel pump and up to the carb. The switch on the dash would then select which tank to draw from. There is a metal line on my '73 that was an emissions deal that I used for a return line in my diesel swap. Maybe someone did the same thing with yours.

Here is a picture of the fuel transfer valve. It is the cylindrical piece located in the upper right corner.

[72-d24]

Where in the fuel line is the electric pump located? They are usually better "pusher" pumps than "pullers".

The fuel pump is just a bit closer to the engine than that fuel filter, about 10" further up the line; so, behind the front bumper and frame and up about 10". I plan to get the mechanical one replaced and switch back to only using this for specific reasons (starting after sitting and hills, mainly).

Just wondering if that was somehow used to fill one tank from the other like a transfer tank. I contemplated that to get a larger travel distance. If it was never on when the issue first happened then it likely wouldn't be the problem.

Actually, when it seemed like we were out of gas in the front tank and I switched it to the back tank (this is a dash switch like the one you describe), the engine still had issues, so I DID flip that electric fuel pump switch trying to help get the fuel from all the way in the back of the rig to the front. That would have been right after the engine started having serious fuel delivery issues but before we noticed the discrepancy in the tanks; so, yes, it was on before the tank issue occurred (although, I don't recall how long I left it on for; seems like I used it most of the day to assist with fuel delivery). That was also the first time I had actually consciously used that switch except to assist with climbing the occasional hill. I had never left it on before then.

Are you saying that it is possible that it is not just a fuel pump, but that it was set up to actually pull fuel from one tank to the other? Do you mean that this set up may be purposeful? That is worth contemplating. I wonder how we would figure out if that is what it does?   Hm?

The receipt for the install clearly states that the purpose was to allow for starting the rig after it sat for a while and I haven't seen anything in any of the paperwork about a fuel transfer. Not all of the upgrades made it into the maintenance logs and receipt book, though, soooo...

The other is if there is a return line that was mentioned by gpw9552. That will bleed off unused fuel and send it back to the tank. If there is only one line it would fill whatever tank that it was run to regardless of the tank being pulled from.

This does sound feasible, too. However, we are pretty sure that there is only the one line leading to each tank. It is too wet to get under there right now to confirm, but I looked at the video that we took of the top of the tank again and I couldn't see a second line.

I don't know much about these things, but it seems to me that this return line would have to come from the area of the carb somewhere, and I don't see a line there either. Also, if the engine wasn't getting enough fuel at the carb at the time, I question whether there would be enough passing through that way to empty one tank and fill the other. Again, though, I don't know a great deal about these things.
Thanks for the reply! Wow! Gives me a lot to think about. Hm? Hm?

[72-d24]

Well, search and search, and I finally found a report of a similar issue:
http://www.classicwinnebagos.com/forum/index.php/topic,5644.0.html

I have quite a bit in common with this guys scenario:

#1 biggest thing in common...flipping a switch appears to transfer fuel from one tank to the other.
2)On both rigs, POs installed electric fuel pumps at similar locations (mine is locate in the front passenger side, a bit behind and above the frame, the other guy's seems to be a little lower than that, about where my fuel filter is).
3)We both seem to have similar tank set ups where the front is the main, the rear is the aux., and the gen is supposed to run off the rear.

At least mine doesn't have a bunch of crazy wiring and fuel routing the way the other guy seems to have going on. My rig only had one owner until he passed about 8 yrs ago (I think). This high ranking military man was rather fastidious about the care of the rig and used it rather solidly until he passed (according to records). It was then sold to its second owner who mainly parked it to use for housing homeless people while he ministered to them and helped them get back on their feet (I feel good about this history). There is not much crazy stuff going on with it. The PO had most of the work done by shops and I have all the records and receipts for that. His maintenance logs show the things that concerned him and what he did to correct the issue. He always went over and above. Heck, the guy paid twice as much for the new rubber roof than I paid for the rig itself.

My point in that is, he may have made a mistake in where and how to install the electric fuel pump, but I feel certain that I am not dealing with crazy mods messing everything up. I have not come across one change on the rig so far that I don't count as a real and true gift and blessing. He cared about his rig and wanted it to run well at all costs (I mean all costs. This guy had a great deal invested in this thing). He wasn't Micky Mousing anything.

From reading on the boards, I understand that it takes a special set up to use an electric fuel pump without causing damage to the mechanical one and possibly elsewhere. I don't think mine was set up with a regulator (would that be on the pump or at the carb?) and it doesn't have return lines. I also understand that, if you do install one, it should be back by the tanks, not up near the engine.

I only learned what that switch does right before I traveled about 125 miles over some very hilly country. I know I didn't have it on before that because the switch has a red indicator light on it. After learning what it does, a relative gave me the idea that it could assist with climbing hills, so I did use it a number of times on hills and then I switched it back off. It was at the end of that leg of the journey that the fuel delivery issues occurred and now my mechanical fuel pump does not seem to work.

Sadly, at this point, my suspicions are that I needed to change that fuel filter a long time ago and then I probably wouldn't have had the issues on the hills. We did look for it a number of times, but we should have really looked harder.

From what I have read on the thread that discusses whether or not to put in an electric fuel pump, I suspect that using it for those hills may actually be what compromised my mechanical fuel pump. I also believe that it wasn't set up to pull fuel from one tank to the other, but that it did do that, probably when it pulled more fuel from the back tank than could pass through that clogged, in-line fuel filter that is up near the engine. In my thinking, that pull created a siphon.

If my suspicions sound reasonable, what do I need to do now? I can't follow that PDF link and diagram from the other post; it is not my set-up and I do better with concepts or specific information. If that electric fuel pump blew my mechanical one and then I drove another 200 miles using it, what other damage could that have caused? Please don't make it something tragic. I am prepared to change a valve in the gas line, but I don't know how I will handle it if someone suggests that I damaged the engine by running it.


Can I just fix the mechanical fuel pump and never again touch that switch, (which does appear to actually BE a self-destruct switch. Oh, the irony...) ?


Let me down gently, k.

[legomybago]

Smell your engine oil..Does it smell gassy? When the diaghram brakes in the mechanical pump, it lets raw fuel pour into the crankcase. Drain the oil and change right away...Replace your mechanical pump and run it. If your not having an issue with vapor lock, no need for having an electric pump in the system. Replace all rubber fuel lines from the tanks forward...

[72-d24]

Thanks!

I checked the dip stick. I don't ordinarily go around smelling oil, but there seems to be an odor to it that very well could be fuel. There also seems to be more of it than there should be.

We are going to change the oil, the fuel pump, the fuel lines all the way back, and maybe that valve.

Anything else? (she asks with trepidation)

[legomybago]

You have a bad pump!! Good job. Sounds like your on the right track.

By replacing/updating all your rubber fuel lines, you will in return understand your system better. You will probably have to drop the fuel tanks down some to reach the sending unit.

[cosmic]

Nice work. you would not want to have fuel in that gas for to long before the bearings start to fail and you have catastrophic engine failure. great find lego

[72-d24]

Update:


Thanks for all the help with figuring this out so far. I take it from the fact that no one has chimed in with an "Oh, sure, fuel can move from one tank to another; happened to me," that it doesn't actually happen very often. I have had 2 people with automotive knowledge in the real world confirm that it can indeed happen and probably did. Both agree that my tank selector valve must be sticking open. That is GREAT news for me because, if that isn't what happened, then I have a huge leak in my back tank to deal with and I have no idea what is going on with the front one.


That valve is $60 and I already put over $200 into the rig this week. I am told the quick fix is to pinch the hose to one of the tanks (to keep the leak from pulling air when it runs out of fuel to pull). Only problem is that my fuel lines from the tanks to the front frame/bumper area are all metal, which I don't want to pinch.


My local NAPA guy is legendary in these parts and was all set to guide me through the issues caused by fuel in the oil. He knew exactly what had happened with only minimal information. I took the oil to him after I drained it. He smelt it and said, "Good news! That's some clean oil!" Shww! 


OK, so no fuel in the oil. He wanted me to take the electric fuel pump out of the system completely. My family kept saying, "But, it got you home." We put plugs on the wires and pulled it; we will carry it along as a "just in case." item. As a side note, I looked at the receipt for its install again and it specifically says, "for starting after sitting for a long time only." Hmmm, if only I had understood how important that word "only" was.   


Thanks for all the input and help with figuring this out. I truly appreciate it!