C2 Fuel Smell and Sending Unit Cam

[John H.]

Re: C2 Fuel Smell and Sending Unit Cam

Roger -

Is the rubber O-ring between the sender flange and the tank (where it belongs), or is it between the lock ring and the sender flange?

[Roger P.]

Re: C2 Fuel Smell and Sending Unit Cam

Hi Larry and John, I checked the electrical connections and took a closer look at the rubber O-ring. The connections do not appear to be leaking, and the O-ring appears to be between the sender flange and the tank. It also looks like the locking cam is on as tight as possible up to the stops. I wiped up the seepage and the small amount that came off was black and thick (I assume partially dried gas). It appears that the O-ring is allowing an extremely small amount of gas to seep out, so I will keep an eye on it for a few weeks before I decide to change the sending unit. This way I can determine if I really need to make the repair (which I most likely do), and also cruise around on the weekends to get my full tank of gas down to near empty. Any thoughts on why I am seeing most of the partially dried gas around the outer edge of the raised ring that the cam tightens against? Is it possible that the tank itself has a pinhole leak there causing the seepage? Thank you, Roger (50141)

[John H.]

Re: C2 Fuel Smell and Sending Unit Cam

Hi Larry and John, I checked the electrical connections and took a closer look at the rubber O-ring. The connections do not appear to be leaking, and the O-ring appears to be between the sender flange and the tank. It also looks like the locking cam is on as tight as possible up to the stops. I wiped up the seepage and the small amount that came off was black and thick (I assume partially dried gas). It appears that the O-ring is allowing an extremely small amount of gas to seep out, so I will keep an eye on it for a few weeks before I decide to change the sending unit. This way I can determine if I really need to make the repair (which I most likely do), and also cruise around on the weekends to get my full tank of gas down to near empty. Any thoughts on why I am seeing most of the partially dried gas around the outer edge of the raised ring that the cam tightens against? Is it possible that the tank itself has a pinhole leak there causing the seepage? Thank you, Roger (50141)

Roger -

Nothing in gasoline is "black and thick" - sounds more like the rubber O-ring may be deteriorating.

[Larry M.]

Re: C2 Fuel Smell and Sending Unit Cam

Roger -

Nothing in gasoline is "black and thick" - sounds more like the rubber O-ring may be deteriorating.

I agree...........or the previous owner used gasket sealant on the o-ring.

Larry

[Roger P.]

Re: C2 Fuel Smell and Sending Unit Cam

John and Larry, I think you guys are right on the money. My brother owns an automotive repair shop and replaced my sending unit over 4 years ago with an imported replacement sender. The old one was shot and was not an original sending unit. It doesn't read accurately (a full tank reads about 3/4 tank, and a 1/4 tank reads near empty), but before it was replaced, it didn't read at all. The ethanol is probably eating at the O-ring as you guys suggest which means the seepage will most likely turn into a drip at some point. It could also be pulling the same deteriorating rubber into the carb and engine . I am going to order the Eckler's "GM Restoration" sending unit that is made in the USA and is resistant to ethanol. I believe that will solve my problem... and hopefully will also give me accurate readings at the fuel gauge. Thank you for your help, Roger (50141)

[Roger P.]

Re: C2 Fuel Smell and Sending Unit Cam

Well, I haven't replaced the sending unit yet as I slowly run the fuel down on weekend cruises. After this weekend, I should be ready to do the job. I was able to find a new Fargo sending unit and returned the one from Eckler's since it wasn't made in the USA as advertised and I wasn't happy with the mechanism & finish. I also decided to buy an extra sending unit rubber O-ring just to have on stand-by just in case I need it in the future. When I checked the gas level in the tank the other day, I stuck my iPhone in the filler hole and snapped a photo. I was surprised to see a very nice looking sending unit (it may be a Fargo unit, but looks even better than the new one I just purchased). The gas tank also looks to be in very good condition, but I do see a few spots around the sending unit tank flange. Are those rust spots? Could that be where the fuel seepage is coming from? Keep in mind that the seepage is "black & thick" when I try to wipe it off the tank, so I still think that is the rubber O-ring deteriorating as John H. suggested. To be proactive, I am now thinking about keeping the existing sending unit, replacing the O-ring gasket, and applying either "Seal-All" or gas-resistant "JB Weld" around the perimeter of the sending unit tank flange on the bottom (outside) of the tank while the gas is drained and the tank is clean. Any thoughts? Thank you, Roger (50141)

[Ken A.]

Re: C2 Fuel Smell and Sending Unit Cam

It appears you have a replacement tank (it looks new). If so, we have found the cam/lock part to not be as tight as the original GM part on some of the repro tanks and thus requiring a slightly thicker O ring to seal. Do not use any "sealers" on the new gasket and the "tab" on the O ring is not needed. Email me if you can't find the proper O ring.

[Gary B.]

Re: C2 Fuel Smell and Sending Unit Cam

It appears you have a replacement tank (it looks new). If so, we have found the cam/lock part to not be as tight as the original GM part on some of the repro tanks and thus requiring a slightly thicker O ring to seal. Do not use any "sealers" on the new gasket and the "tab" on the O ring is not needed. Email me if you can't find the proper O ring.

Ken,

Does your comment about the cam/lock not being as tight on some repro tanks apply to the repro tank sold by Quanta?

Gary

[Ken A.]

Re: C2 Fuel Smell and Sending Unit Cam

I believe they come with a thicker O ring.

[Roger P.]

Re: C2 Fuel Smell and Sending Unit Cam

Hi Ken. Thank you for your reply. I purchased a new O-ring and cam lock, so I hope that it will seal up tightly. If that is where my seepage is coming from, then I will be in good shape. However, I am concerned about those marks that I see in the photo at the inside bottom of the tank around the sending unit flange. Do you think they are rust spots - perhaps from manufacturing welds - that developed a pin hole which is causing the seepage? As I mentioned before, because I am wiping off thick, black residue, I assume it is the O-ring deteriorating from the ethanol. I suppose there isn't any harm in putting a bead of Seal-All around the flange on the outside bottom of the tank to make sure . Roger (50141)

[Joe L.]

Re: C2 Fuel Smell and Sending Unit Cam

Ken,

Does your comment about the cam/lock not being as tight on some repro tanks apply to the repro tank sold by Quanta?

Gary

Gary-----


I believe that all reproduction/replacement Corvette fuel tanks are actually manufactured by Spectra Premium Industries. For Quanta they manufacture a run of the tanks with the O.L. Anderson embossed logo; for all others the logo is omitted.

[Ken A.]

Re: C2 Fuel Smell and Sending Unit Cam

There are tanks being made in China that are cheaper than Spectra.

[Roger P.]

Re: C2 Fuel Smell and Sending Unit Cam

I finally got the opportunity to tackle the project on Friday afternoon with a successful result, but... After removing the sending unit, it was obvious that the seepage was coming from a crack in each of the white plastic pressed-in parts that hold the metal contacts to the sending unit, as well as deterioration of the small black seals/O-rings that are installed between the metal base and the plastic parts. Larry, you nailed that one! The black seals looked like they were "melting" from the ethanol. My new Fargo unit is fabricated with metal contacts that are held in place with threaded nuts and a different type of seal/gasket (I assume ethanol resistant). If the sending unit leaks in the future, I should be able to fix the problem by tightening the two contact nuts without having to buy a new unit. When we installed the unit with the new rubber O-ring seal & locking cam, the cam turned to full lock by hand without using the cam wrench. Upon comparing the new O-ring (which I soaked in oil for a couple days) to the old O-ring, there was clearly a difference in thickness between them. Ken, you were right about the repro O-rings (my tank may have been replaced many years ago, but it has the O.L Anderson logo)! When we installed the unit with the old O-ring and new cam, it tightened properly with the wrench. OK, now all we had to do was clean the connectors on the harness and pop them on, but... The connectors wouldn't stay on the sending unit contacts because the contacts were smaller in diameter by a fraction than the contacts on the old sending unit. Give me a break! Thankfully, with some careful plier "squeezing" of the connectors, we were able to get them on with a snug fit. Once some fuel was put back in the tank, I got a reading on the fuel gauge... success! I went to the gas station and put in just shy of half a tank to make sure there weren't any leaks before topping her off, and the gauge showed below 1/2 full. It may not be 100% accurate, but it's close enough for a '65 Vette... and no more fuel seepage!

Roger (50141)