Warning, Will Robinson

Subject:  VDO 221-012D fuel sender used in several Zenith models.

I have a four-year-old, Rotax912ULS powered CK-750 Cruzer with 350 hours.

After the condition inspection, I went on a once-around-the-pattern maintenance flight.  While turning a right base leg, fuel came out of the left wing root and down across the left door.  After landing, took off the inspection plate to look for the problem.  Could not see anything unusual.  After talking to my advisor, decided to add fuel to troubleshoot.

Well, the gas poured out.  Since i had the inspection plate off, looked in and saw the gas pouring out the center of the fuel sender.  Quickly drained the fuel.  Though the inspection hole, felt the center of the sensor.  It was lose and the white plastic piece was completely gone.  Removed top wing root pane and fuel sensor.  I could see light through the wiring terminal in the center of the sender.  The plastic piece had completely dissolved.  Sent an e-mail to Zenith about the problem.  Roger replied that it was probable additives in the fuel.  Kind of a "duh".

I always used lead free, ethanol free (or so the label says) 91 octane auto fuel.   What other additives in the fuel are plastic dissolving?  Who knows?

I am now installing two new fuel senders.  Don't look forward to doing this every three or four years.

One thing, if it happens to you while in flight, on the Cruzer at least, there is five plus gallons of fuel remaining.  The chance of both senders failing at the same time is nil so you have enough time/fuel to get to an airport or back to home base.

Hope Zenith finds a direct replacement for the VDO 221-012D sender or VDO improves the plastic quality.

Photo, left to right:  left wing, new sender, right wing.

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I wish you had posted this before you installed the new senders! Those VDO senders are automotive and originally designed to be mounted on the top of a fuel tank (such as a VW) and not intended to be constantly immersed in fuel.  There have been numerous reports of the white center insulator either becoming loose, crumbling, or just falling out!  I had leaks from both senders (at the same time!!!) and replaced them with Stewart Warner senders which are very similar except they have a couple of major improvements:  they don't have the white plastic insulator and use a thick-film resistor instead of the wound-wire resistor in the VDO.  These are used in Van's RV's and mounted similarly (on the side of the tank and not on top) and I've never seen a report of one leaking even after many years of use.  Van's recommends NOT using the rubber seal and instead using Pro-Seal sealant.

If you've already installed the VDO senders, I would recommend sealing-over the white plastic insulator with Pro-Seal or Chem-Seal (same thing as Pro-Seal).

I posted about this problem here:  VDO Fuel Sender Woes .



Thanks, John

Read your Oct 2020 entries and all the replies. Next time.

You would think that Zenith would have come up with a cure like yours by now.

Oh, well

I had both of my VDO fuel senders leak around the 70hr mark. I replaced the plastic insulator with a pressed and welded in 8mm stainless steel tube, ran a new wire through the tube and potted the wire in place with an epoxy rated for fuel submersion. No leaks or other issues in 200+ hours now.

Wish I would have known these were so prone to leak when I was building. I would have just gone with a vertical mount fuel sender and access panel but with the hole already in the side of the tank it was much easier to just make the existing senders work.


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