Fuel tank lock ring troubles

[DrCharles]

As I posted in the "What did you do with your truck" thread, I just finished installing two new fuel tanks, a selector valve and re-plumbed all the flexible lines with diesel-rated (30R7) fuel hose. But the lock ring on the rear tank started leaking a lot onto the ground as soon as I filled it. The front tank seems to be OK but I didn't fill it all the way to the top, either. Tomorrow I will pull the bed again and redo the rear lock ring.

The front tank is a Spectra Premium and the rear is a Platinum Pro, both from Rock Auto. When I put them together, the lock ring and o-ring did not look like a good design - there is no groove for the O-ring to sit in! Both the tanks and the pickup/sender flange just have a (hopefully) flat surface. I did lube the o-ring, too. What stops the o-ring from wallowing around and getting out of position while I'm tapping away at the tabs with a hammer and punch? I'm pretty sure that's what caused my rear tank leak, will know for sure tomorrow.

I have read many threads, and reviews on the Spectra LO-04 and Dorman replacements, and some say that the supplied O-ring is too large in diameter. Most had no problems, though.

My local O'Reilly had this one in stock: https://www.oreillyauto.com/detail/...g-unit-retainer/55812/4528752/1993/ford/f-250

Any thoughts before I try again tomorrow?

 

[Macrobb]

o-ring goes under the sender, between the tank and the sender. The lock ring doesn't need any groove, because the sender has tabs keeping it from moving around.

 

[DrCharles]

oh yeah, I said that wrong No worries, the o-ring is between the tank and the sender flange!

There is no groove holding the O-ring (not the lock ring, which can't move very far off-center) in place though. So my question is still relevant - how does the O-ring stay where it belongs...

 

[genscripter]

There is no groove holding the O-ring (not the lock ring, which can't move very far off-center) in place though. So my question is still relevant - how does the O-ring stay where it belongs...

I don't think my sender o-ring seal had a groove either. It had a lower level that helped to keep the o-ring about the right place: http://www.nickpisca.com/diesel/fue...di-van-center-diesel-tank-sender-replacement/ But to make sure that it didn't slide when I torqued down the lock ring, I used some sticky synthetic grease to "adhere" the oring in the lower level flange, and that seemed to keep it from walking on me when I finished the lock ring rotation. HTH

 

[genscripter]

Also, I liberally applied anti-seize to the lock ring and its receiver, so that it shouldn't be prone to rusting and seizing. Also, if I had to pull this apart, having the anti-seize on the lock ring should make it easier to unscrew. I know when I took it apart, it took some decent tapping around the ring to break the existing rust free.

 

[franklin2]

oh yeah, I said that wrong No worries, the o-ring is between the tank and the sender flange!

There is no groove holding the O-ring (not the lock ring, which can't move very far off-center) in place though. So my question is still relevant - how does the O-ring stay where it belongs...

A helper? To keep down pressure on the sending unit while you tighten the lock-ring?

 

[icanfixall]

use some super glue on the o ring seal to the tank. Then it will hold in place. In my harpooning of both tanks I used permatex ultra copper plus rtv to seal in the new air vents. I put that **** of everything...

 

[DrCharles]

interesting idea! But super glue is what they use to stick the two ends of O-ring stock together when making new ones... and when pull-tested to destruction they always break somewhere other than the joint. If I ever have to replace the O-ring (or tank) again, how will I get it off?
I may try just a couple of spots to tack it in place. As Franklin2 pointed out, the O-ring won't move if a helper is stabilizing the pickup flange.

 

[DrCharles]

OK. The (day-)old o-ring was obviously squeezed out too far at one point. And it's too big for the sealing area on the tank. The new one is exactly the same. I think the Platinum Pro tank has a slightly mis-sized flange.

So I made the o-ring smaller via razor blade and Permatex-brand super glue. It really works, too! It's just as strong there as anywhere else. Put it on (with a little dab of Aviation Sealant #3 at the gap area, just in case) and siphoned the bucket of diesel back into the tank.

I think it's still seeping just a tiny bit... it's hard to blow it all out even with compressed air since there are so many nooks and crannies for a couple of drops to hide and roll back downhill.

If it's still moist, what's the next move? Keep trying different size O-rings (or order a couple in Viton from McMaster at $9 apiece)? Coat the entire O-ring with the #3 Permatex, or some flavor of RTV? At this point I don't care if it ever comes off again

 

[DrCharles]

Nope... still seeping. Tried a new lock ring that fits tighter and has locking bumps, same problem.

After looking at the original tank and the "Platinum Pro" (Taiwan), the problem is that the groove for the O-ring is not stamped fully flat at the bottom. So a square O-ring will never seal properly there. I really don't want to drain it, remove and ship it back to Rock Auto although I will NEVER buy that brand again!!

At this point I'm just going to seal the bottom of the groove with RTV, assemble and let it cure until tomorrow before siphoning the bucket back in another time. Meanwhile I'm going to call Rock Auto this week and see what they can do for me. The smarter move is probably to buy a Spectra Premium tank and worry about returning this one later. With the bed off it's only four more bolts!

 

[lotzagoodstuff]

Loctite 515 or 518 will seal this up, 518 is a little more flexible. Either should cure for 24 hours before exposing them to diesel fuel.

Good luck

 

[franklin2]

I would think permatex sealer would also be a little bit more resistant to the fuel than silicone. I do not know how silicone reacts to diesel fuel, but I know it turns to a slimy goo when it gets against gasoline.

 

[DrCharles]

Yes, it specifically says (as do all the silicones) not for parts continuously exposed to gasoline.

The tech data sheet for RTV red says, "The product retains effective properties in contact with automotive fluids, such as motor oil, transmission fluids, alcohol and antifreeze solutions. Note: Not recommended for parts in contact with gasoline." It's strange that they don't mention diesel at all, just gas.

I figure if it can handle oil and ATF it might be OK for the small amount of diesel with little if any pressure behind it. But we'll see

 

[icanfixall]

The ultra copper plus works great on gas, diesel or anything ya got. Possibly you "could make an o ring slightly larger in diameter than the original one you have that leaks now.

 

[DrCharles]

Actually the standard square one that came with the tank (and with the replacement lock ring) is already too large an ID. I had to cut out about 3/16" and super glue the ends back together.

On second thought, did you mean a thicker O-ring? That would make the sender flange fit tighter but would worsen the problem of a tank flange groove that is not flat on the bottom. Does anyone make O-ring cord with a D-shaped cross section? It would seal properly to both surfaces