Need help with leaking fuel sensor gasket

[Bill Knecht]

Can anyone help me with this problem? I installed a new fuel sensor on my 1971 Massey-Ferguson 135, and it now leaks fuel out the top of the fuel tank when driving, as the fuel sloshes. I tried gooing it up with Form-A-Gasket, but no luck. Then I tried putting nylon washers over each of the 5 hold-down screws. No luck. What's the trick to stopping this leak? The gasket itself is cork, and the seal it needs to perform is obviously complex, as you can see from the picture. It's not a simple seal of two flat surfaces, and fuel clearly leaks out of the screw holes.

I apologize if this has already been discussed. I tried the Search function, and it came back with too many pages to read them all.

 

[stevieb49829]

Can I assume that your hold down screws go into a thread ring underneath the tank sheet metal? Or some other type of "thickening" for the tapped threads? And then your gasket fits between the sheet metal tank and the sender head? If that's true, then if your gasket is sealed down on both clean, smooth surfaces (using something like petrol-proof Permatex), your nylon washers should stop that leak at the screws. Again, a little Permatex on both sides of your washers may help. Formagasket, or any silicone sealer does not do well in a fuel environment, especially with ethanol in the fuel. What's the metal strap under the one screw? That's a leak waiting to happen. Also, some cork has a tendency to wick liquids through its edges, but if it's the supplied gasket for this application, it should not be the problem. There is a possibility of an almost invisible crack in the sheet metal or the aluminum head too. steve

 

[Bill Knecht]

Can I assume that your hold down screws go into a thread ring underneath the tank sheet metal? Or some other type of "thickening" for the tapped threads? And then your gasket fits between the sheet metal tank and the sender head? If that's true, then if your gasket is sealed down on both clean, smooth surfaces (using something like petrol-proof Permatex), your nylon washers should stop that leak at the screws. Again, a little Permatex on both sides of your washers may help. Formagasket, or any silicone sealer does not do well in a fuel environment, especially with ethanol in the fuel. What's the metal strap under the one screw? That's a leak waiting to happen. Also, some cork has a tendency to wick liquids through its edges, but if it's the supplied gasket for this application, it should not be the problem. There is a possibility of an almost invisible crack in the sheet metal or the aluminum head too. steve

Thanks for the reply, Steve. I've not felt underneath the hole the sensor fits into, but agree there's probably a ring under there, otherwise the sheet metal of the tank wouldn't hold a tap very well. Yes, the gasket fits between the top of the tank and the sender head, so the surfaces are as you say.

The sealant I tried to use may well be the problem, as you discuss. I used Permatex 80017, which is supposedly gasoline & oil-resistant. But, I noticed little shards of it coming loose, which supports your statement of that not doing well in a fuel environment. Either that, or maybe I didn't let it dry long enough before it got exposed to the diesel. Some of these shards are probably now in the tank, my bad, although I had previously installed a high-quality Donaldson P551039 fuel filter, which should thankfully catch any of those critters.

Maybe I should try fuel-resistant Permatex 85420. Can I dab some of that on the base of those 5 screws as well, and still be able to remove the screws later, if necessary?

That little metal strap is meant to be the OEM electrical ground for the sensor. I agree it looks problematic from a leak perspective.

Thanks for your input. This helps a lot.

 

[Fritz Maurer]

It looks like the sender cover is stamped as a cup as opposed to a flat plate. If so, the gasket may not be thick enough… the sender cover is contacting the surface of the tank before the gasket is sufficiently compressed.

 

[Bill Knecht]

It looks like the sender cover is stamped as a cup as opposed to a flat plate. If so, the gasket may not be thick enough… the sender cover is contacting the surface of the tank before the gasket is sufficiently compressed.

Hello, Fritz. You're right. The sender cover is a cup, not a flat plate, and you pose an excellent question. I'll bet I could augment the gasket's thickness easily. That's definitely worth a try. Thank you, Sir !

 

[Dieseltech]

Some MF tractors had small a O ring under each screw head, when the get hard and brittle they will leak over time.

 

[stevieb49829]

Thanks for the reply, Steve. I've not felt underneath the hole the sensor fits into, but agree there's probably a ring under there, otherwise the sheet metal of the tank wouldn't hold a tap very well. Yes, the gasket fits between the top of the tank and the sender head, so the surfaces are as you say.

The sealant I tried to use may well be the problem, as you discuss. I used Permatex 80017, which is supposedly gasoline & oil-resistant. But, I noticed little shards of it coming loose, which supports your statement of that not doing well in a fuel environment. Either that, or maybe I didn't let it dry long enough before it got exposed to the diesel. Some of these shards are probably now in the tank, my bad, although I had previously installed a high-quality Donaldson P551039 fuel filter, which should thankfully catch any of those critters.

Maybe I should try fuel-resistant Permatex 85420. Can I dab some of that on the base of those 5 screws as well, and still be able to remove the screws later, if necessary?

That little metal strap is meant to be the OEM electrical ground for the sensor. I agree it looks problematic from a leak perspective.

Thanks for your input. This helps a lot.

Bill, if you get a good sealant, I'd plug the screw threads with it, a little extra under the head (or both faces of the nylon washers) and snug them down. Or replace the orings mentioned above. I have yet to find a gasket cement that would act as a thread locker, so you are probably good there. Dieseltech. as his name implies wades through that fuel on a daily basis. I'm a gas-kind of guy. So his advice is more valuable than mine in this situation (and most others!). Others may suggest a good sealant. I can't even read the label on mine anymore. I'd just make sure both surfaces are really clean and level, and once clean, look carefully for any hairline cracks. If I'm not mistaken, one of the studs is a ground, so that little tab is redundant, and could be discarded. steve

 

[504]

Buy a can of Gasiol thread sealer (I spelled it wrong) that stuff is made for fuel and oil products. It is the best I have ever found. Any good hardware store should have it.

 

[Hobo,NC]

Thanks for the reply, Steve. I've not felt underneath the hole the sensor fits into, but agree there's probably a ring under there, otherwise the sheet metal of the tank wouldn't hold a tap very well. Yes, the gasket fits between the top of the tank and the sender head, so the surfaces are as you say.

The sealant I tried to use may well be the problem, as you discuss. I used Permatex 80017, which is supposedly gasoline & oil-resistant. But, I noticed little shards of it coming loose, which supports your statement of that not doing well in a fuel environment. Either that, or maybe I didn't let it dry long enough before it got exposed to the diesel. Some of these shards are probably now in the tank, my bad, although I had previously installed a high-quality Donaldson P551039 fuel filter, which should thankfully catch any of those critters.

Maybe I should try fuel-resistant Permatex 85420. Can I dab some of that on the base of those 5 screws as well, and still be able to remove the screws later, if necessary?

That little metal strap is meant to be the OEM electrical ground for the sensor. I agree it looks problematic from a leak perspective.

Thanks for your input. This helps a lot.

80017 is great where both parts are precision machined it does not fill gaps are voids so not for your application. 80020 is fuel resistant RTV it will fill gaps and voids, personally I would shy away from it if possible. The cork gasket should seal it a sealer is not your fix.

 

[Mule Meat]

From the looks of the screws. Someone got a little excited with a screwdriver.

Good chance that the metal of the cover around the screw heads is dimpled or concaved. If that is the case. The metal is hitting the tank before the screws are tightened properly. Not to fear . Laying the cover upside down with the screw holes on a flat piece of metal. A socket type object just a tad larger than the screw hole can flatten it back out with a tap of a hammer.

 

[caterpillar guy]

IF the cork gasket is an older one it might be a bit dried out. Soak it in water over night then dry off and install. this will swell it back up some and make it more pliable so it will conform to any defects in your tank and sender. Then I would use some copper washers under the screws if they go through which I would guess they do. Tighten your screws evenly and don't over tighten. If the sender is puckered from the previous tightening do as Mule said with a flat plate and socket or other round of flat piece on the hole area.

 

[Fritz Maurer]

I wouldn’t go pounding on that sending unit…there must be a less Neanderthal way of correcting that condition, if that’s what it turns out to be…

 

[Janicholson]

IF the cork gasket is an older one it might be a bit dried out. Soak it in water over night then dry off and install. this will swell it back up some and make it more pliable so it will conform to any defects in your tank and sender. Then I would use some copper washers under the screws if they go through which I would guess they do. Tighten your screws evenly and don't over tighten. If the sender is puckered from the previous tightening do as Mule said with a flat plate and socket or other round of flat piece on the hole area.

Not a flame, just experience. Do not use a copper washer on an aluminum, or pot metal component. The combination created real electrolysis and will corrode radically. Jim

 

[Bill Knecht]

Bill, if you get a good sealant, I'd plug the screw threads with it, a little extra under the head (or both faces of the nylon washers) and snug them down. Or replace the orings mentioned above. I have yet to find a gasket cement that would act as a thread locker, so you are probably good there. Dieseltech. as his name implies wades through that fuel on a daily basis. I'm a gas-kind of guy. So his advice is more valuable than mine in this situation (and most others!). Others may suggest a good sealant. I can't even read the label on mine anymore. I'd just make sure both surfaces are really clean and level, and once clean, look carefully for any hairline cracks. If I'm not mistaken, one of the studs is a ground, so that little tab is redundant, and could be discarded. steve

"Great minds run in the same gutter", as my sister used to say. Yesterday, I had exactly the same idea, Steve -- plug up those screw holes with sealant. I'm thinking it might be best to take out the new sensor completely, redo the sealant, and then just let it cure for a couple of weeks before putting it back in the fuel tank.

I believe you're right about one of the terminals being ground. The other one goes through the oil pressure cutoff switch, so that current stops flowing to the fuel sensor when the engine stops running.

 

[Bill Knecht]

Some MF tractors had small a O ring under each screw head, when the get hard and brittle they will leak over time.

You know, I wondered that same thing myself. Being a'71, this thing's over 50 yr old. Rubber washers just don't last that long, esp. when subjected to UV and oxygen. That's why I tried nylon. Of course, I could get anything made on the planet, by going to McMaster-Carr -- if I didn't mind buying 10x as many as needed & taking out a second mortgage on the house to pay for it (once you add S/H).

 

[Bill Knecht]

Buy a can of Gasiol thread sealer (I spelled it wrong) that stuff is made for fuel and oil products. It is the best I have ever found. Any good hardware store should have it.

Interesting! Thanks for the tip. I'll look this up. Here it is:
Gasoila

 

[Bill Knecht]

From the looks of the screws. Someone got a little excited with a screwdriver.

Good chance that the metal of the cover around the screw heads is dimpled or concaved. If that is the case. The metal is hitting the tank before the screws are tightened properly. Not to fear . Laying the cover upside down with the screw holes on a flat piece of metal. A socket type object just a tad larger than the screw hole can flatten it back out with a tap of a hammer.

Roger that on the screws. T'wasn't me. I do know better than that. That's a good tip, re the metal surface. I'm going to check that out.

 

[Bill Knecht]

IF the cork gasket is an older one it might be a bit dried out. Soak it in water over night then dry off and install. this will swell it back up some and make it more pliable so it will conform to any defects in your tank and sender. Then I would use some copper washers under the screws if they go through which I would guess they do. Tighten your screws evenly and don't over tighten. If the sender is puckered from the previous tightening do as Mule said with a flat plate and socket or other round of flat piece on the hole area.

The cork gasket is the one that came with the new sensor when I bought it. The previous one is rubber. I had tried using that rubber gasket, but it leaked like crazy. So, trying this cork gasket is "Experiment #2".

Copper washers -- interesting. They would be softer than steel, and probably available at Lowes or another big hardware store.

 

[Bill Knecht]

I wouldn’t go pounding on that sending unit…there must be a less Neanderthal way of correcting that condition, if that’s what it turns out to be…

The surface of the sending unit seems pretty flat, given that it's new. But, as a philosophical point, you do have a point.

 

[Bill Knecht]

Not a flame, just experience. Do not use a copper washer on an aluminum, or pot metal component. The combination created real electrolysis and will corrode radically. Jim

I hadn't thought of that. Thanks for bringing it up. Remembering my college chemistry, the copper would be the electron donor, and would do most of the corroding, correct?