The electrical post w/white plastic insulator on one of our VDO fuel tank senders pivots, and the other does not.  We did not notice this movement before, and there was no leakage during our static leak test 18 months ago.  Now that the wings are installed and we're getting ready to fill the tanks, we checked the electrical connections and noticed this movement.  Since we do not know how the center post of the VDO is constructed, we do not know if this is a problem.  Don't want to replace unnecessarily.

Has anyone else experience the center electrical post movement and is it a problem?


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I don't think it should be loose at all - it was a long time ago, but I don't recall my VDO senders' insulators moving while manipulating them to plug in connectors, etc.  6 years and 550 hrs, I haven't had a bit of trouble with mine and not a drop of fuel leakage, but some time ago one (or more?) builders reported they had an insulator so loose IT FELL OUT!  Yikes!  If I recall correctly, they used JB Weld epoxy to secure them and had no more problems.

Since they're already installed and in the wings, I'd either put a bead of JB Weld or Pro-Seal around the insulator, then fill the tank and let it sit for a while and watch for leakage.  (I repaired a crack in the bottom of an aluminum 250 gal fuel storage tank on my farm with JB Weld about 30 years ago and it is dry as a bone to this day!) Alternatively, you'd never go wrong to replace the sender, but that's a difficult job when everything is buttoned-up inside the wing!



Thanks for the reply John.  Our root wing skin has not been riveted yet so it'll be relatively easy to replace, just don't want to if unnecessary.  Unfortunately, I cannot find anything showing how the sender is constructed/sealed.

Here's the post about the loose insulators :

The original poster describes them as a press-fit.  Seems to me it would surely have a little sealant of some sort, but if it moves, then obviously the seal is broken!


This is a good read.  I spoke with Roger this morning and asked if he would find answers for me.  He says he'll get back with me on Monday.  Roger also says Zenith will replace our fuel sender if it's found to be bad.


Our root wing skin has not been riveted yet so it'll be relatively easy to replace ...

By the way, I did the same thing - I had my wing root skin painted separately and once the plane was fully assembled after painting, I filled my tanks and let the plane sit for a day or two to watch for any leaks around the senders.  Then, once I was certain the senders were bone-dry, I installed my wing root skins and touched up the rivets with paint.

Knowing what I know now, top-mounting the senders makes a lot more sense - that's the orientation they were designed for, anyway! However, my build was several years ago and I don't think the insulator problem had come up then.  It's been speculated perhaps later than my build the manufacturer had a bad production run of senders.  Also, when I bought my kit, it was partially completed and the original builder had already cut the holes for the senders per plans. 


This is what we plan to do.


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