Zenith Aircraft Fuel Sender Replacement Nightmare

I have had never-ending problems with fuel drains and fuel sender leaks for the 2-1/2 years my Zenith CH601 XLB has been flying.

I finally fixed the fuel drain leaks by using the longer fuel drain plugs (Curtis CCA-2500).

The problem with the senders was that I was getting frequent drips around the screws on both tanks. I would try and reseal them with the Permatex white fuel sealant, but it never seemed to hold for long.

Then I noticed my pilot side tank was leaking a lot. I pulled the access cover and fuel was seeping out of half of the screws, and possibly the middle terminal.

When I touched the sender, the terminal insulator cracked and a large chunk just fell off. Time to replace.

I ordered a new sender and gasket kit from Zenith ($43).

Removing the sender was quite easy. Getting the new one back in would be a different story.

At the time I also noted some seepage around the hose connector at the tank so I unscrewed that and pulled it out.

What struct me about this was the hardened Permatex. It was very hard and cracked apart when pressure was applied. I know this is used a lot with success but I couldn't help thinking that normal vibration, and time, could cause this stuff to crack and possibly lose seal. I wire-brushed off the old Permatex and used EzTurn on it before reinstalling.

I took a close look at the old sender. I have put 300 hours on my plane and have run about 50% mogas and 50% 100 LL. I was curious how the rubber (viton?) gasket had held up and suspected that was part of the leak problem.

I was wrong. The gasket looked perfect except for spots of the hardened Permatex on it. Again, I wondered if the hardened Permatex was leading to leaks since it could create a gap between the gasket and the tank.

To be clear - I have no real evidence that the Permatex had lead to any leak issues. However, after some research, I decided to use EzTurn on the re-install. I liked the idea of a product that never hardened and remained resilient.

A 5oz tube of this will last a lifetime.

One thing that bothered me when I had previously tried to stop the units from leaking was not knowing how much torque to apply to the screws. I was just using a normal screwdriver and had no idea of what I was doing was too tight or not tight enough.

I had recently bought a $100 torque screwdriver and was looking forward to KNOWING I had applied the correct torque. After looking up the torque value for #8 screws in the Lycoming manual, I learned the torque should be 20 to 22 inch pounds.

Just because this torque value applied to Lycoming screws didn't mean it was right for this "Made in India" fuel sender unit. So, I practiced on the old sender first and came to the conclusion that 20 inch pounds seemed about right and decided to use that setting.

I had read elsewhere that it helps to practice this install before you lube stuff up and start installing, so I did.

And right here began a tremendous amount of frustration! ARGHH!!1*%$!

First, while sitting a my hangar desk I tried to simply screw the 5 screws back into the sending unit, thru the gasket and into the back plate. Simple right? An hour later, cursing and quite literally screaming, and slammed the hangar door and went home after failing this stupid simple task.  

This is probably a good time to mention that I live with a lot of pain and doing just about everything hurts me. This leads to a very low stress tolerance. I get frustrated and stressed as my pain continues to increase.

I came back the next day and after another 45 minutes I finally got the friggen 5 screws back into the old sender while sitting at my desk!

There is something about the tight tolerance of the holes in the sender and backing plate and the holes in the gasket. Unless everything is aligned perfectly they will not go in.

Next I began the install of the new sender. I used the ExTurn on both sides of the gasket and all of the screws.

As per the instructions I put the long screw in first and tried to fit the backing plate thru the hole in the tank. An hour later, cursing and quite literally screaming, and slammed the hangar door and went home after failing this stupid simple task!

The next day I tried again and nothing I could do would get the backing plate thru the hole in the tank. Then I thought I had discovered why:

The new backing plate is on the bottom, the old one on top. The cut-out in the new plate was about a 16th of an inch shallower than the original. After filing the new one down, I went back to the install thinking I had finally solved the problem.  An hour later, cursing and quite literally screaming, and slammed the hangar door and went home after failing this stupid simple task!

You may think I am exaggerating here for the sake of a good story. I am not. I was three days into this install and had gotten absolutely no where - except having a whole lot of physical pain to show for it.

The next day I tried again. Frustrating attempt, after frustrating attempt, failed. The bloody backing plate just would not go thru the hole!

I was about to give up for the day when I tried on last time. By some miracle (I have no idea why) the backing plate went thru the hole!

Woohoo! Almost done now.

Wrong.

No matter how I tried I could not get another screw lined up to screw into the backing plate. An hour later, cursing and quite literally screaming, and slammed the hangar door and went home after failing this stupid simple task!

Day 5. My anxiety, stress and pain is eating at me even before I get to the hangar. I am quite literally considering selling the plane because this kind of stress, and the pain that goes with it, is more than I want in my life.

It took me almost 2 hours to get the second screw started. This is while lying on my back cutting the crap out of my hands on the sharp metal edges of the access opening, and the rib opening. The whole inside of the wing is, quite literally, a bloody mess. There is blood everywhere.

Once I was able to get the second screw started and tightened down, the rest were fairly straightforward. I progressively torqued down the screws with the torque screwdriver, starting at 5 inch pounds, then 10, then 15 then 20 using an opposite screw pattern.

Woohoo! I'm done.

Wrong.

When I try to screw down the grounding plug to the sender the terminal comes apart. Are you friggen serious??? ARGHH!!1*%$!

Ever tried to strip a 4" wire in a extremely confined space and install a new terminal? The tools won't fit in the space.

An hour and a half later the new terminal is on. If there was blood before, the inside of the wing now looks like the St. Valentine's Day Massacre.

After reconnecting the terminals the install was done.

The view from inside the tank (using a harbor freight borescope and taking a cell phone pic of the screen).

The thought of having to start over on another day for the other sending unit was more than I could bare. So I bit the bullet and pulled out the other sender, wire-brushed off the old Permatex, put a new gasket in (though the old one looked perfect, even after all the mogas) and applied EzTurn on the screws and both sides of the gasket. I then torqued the screws to the 20 inch pounds.

After a very long day of work I managed to get the second sender back into place and refilled the tanks to check for leaks.

I came back the next day, did a test flight and re-inspected. No leaks so far.

It's been a week and a half since this ordeal and the dozen cuts on my hands are finally starting to heal.

In the end I decided that if either sender ever leaks again, it is a sign from God that its time to sell the plane.