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Round or Square O-Ring Sending Unit - Help Me Decide

lmelmed

Jr. Member
Joined
Sep 24, 2015
Messages
52
About to reinstall the sending unit. the prior square o-ring was clearly twisted and i suspect the cause of my leak.

i have a new "square" o-ring and a round cross-section o-ring that seems like the right size. I will use vaseline.

seems like the forum responses are split on whether i should go with the square profile or the round profile.

Anyone care to push me in one direction or another, or just flip a coin?

PS - any tips for reinstalling the main fill tube and main vent tube? i.e. can i put a little vaseline on them? They are relatively new (1-2 years).
 

vintage bronco

Sr. Member
Joined
Feb 8, 2010
Messages
850
use the square cut one do yourself favor fit sending unit in tank W/O oring & make sure the two locating tabs fit snug in tank if not bend them carefully so they fit in slots snug then install with new oring I have found them sometimes one tb not locating and when you tighten sender it turns slightly deforming oring, also use brass so it no sparky. hope this helps.
 

MarsChariot

Contributor
Planetary Offroader
Joined
Oct 12, 2004
Messages
2,469
Loc.
Albuquerque, New Mexico
It has been decades since I have seen a round cross-section o-ring. The last few have been square cross-section and have been hit or miss. I say give the round one a try and tell us if it works and where you found it.
 
OP
OP
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lmelmed

Jr. Member
Joined
Sep 24, 2015
Messages
52
Thanks. Maybe I am using the wrong term. The round o-ring is just like a regular o-ring. It does seem a little thicker/larger than the squared one that came with the new lock ring. I’ll snug them up and see which one feels better. Thanks for advice!
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
the square o-Ring is uses in this case as an end seal and provides more surface area and is apt to stay in place. round O-rings are much cheaper and normally used in presion groves and precision bore none of which you have in this application.
 

72_EB

Contributor
66to77
Joined
Feb 4, 2003
Messages
4,962
Use the square one. It is usually much easier to do with the tank out so you can install looking down at the seal so it doesn't shift on you.
Use some lube. I also usually have better luck with a factory retaining ring over and aftermarket even if using a new sending unit.
On filler hoses, do a quick spray of brake cleaner on the ends and install quickly after. It will evaporate quickly, but aid in installation.
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
square, and always try to reuse the original sender lock ring, replacements never seem to lock right or pop off.
 
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