I think it needs a hole in the top to allow ALL the air to escape.

 I think it needs a hole in the top to allow ALL the air to escape.

It has a smallish slit on the top but I think a larger escape hole for the air would benefit the design. One could always drill an additional 1/16 hole with a hand mandril very gently into the white plastic cap on the top. I think Dave WM took one apart. Would it be safe to drill through the plastic cap?

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2 hours ago, dmorales-bello said:

I guess I go way back before you guys! . I was thinking of making a bear skin outfit for Raquel Welch in 2000 BC. My mind keeps going back to cutting and sewing, I suppose.

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Miss fuzzy britches..

here is one for you

"come on bobby pin....pop"

Dave. Dave!       Come back!!   Dr. Dave asked you a question:

10 hours ago, dmorales-bello said:

 I think Dave WM took one apart. Would it be safe to drill through the plastic cap?

Haha!!

So Dr. Dave, I don't think there would be a lot to be learned from a post mortem on the dead one. The only really interesting thing would be to characterize the thermistor against a temperature curve, but if it's open circuit, that won't be possible. I guess there's a tiny but non-zero possibility that the open circuit break is somewhere I could see and kluge together long enough to take some measurements. There is also a tiny, but non-zero possibility that there might be a part number on the outside of the sensor?

Up to you if you want to waste the dollar it would cost to mail it.

11 hours ago, dmorales-bello said:

2000 BC?

The original reference to Darmok is from a Star Trek episode where they encountered a race that always spoke in metaphor. In that situation, you can understand the WORDS, but they really mean nothing unless you have a shared past experience.

For example, you could ask "How is the weather?", and I could answer "Dave WM and Captain O riding in the Z."           Haha!!!

Ok, hope this helps. I have both the original and a new ZCD unit on my bench. Removed the original and had the tank cleaned. 
original unit has 4 holes on the side. Two right below the clamp and two more near the bottom both on opposite sides. The one from ZCD only has three holes on the bottom and a narrow slot on the top for the wiring. Here’s a video of my original 78 unit. Excuse the shaky hand. 

CO, I did a little autopsy and carefully removed the plastic cap from my original thermistor. It looks like a very simple single wire resistance, and it was broken off the bottom (pic below) . I found no resistance in removal of the plastic cap and the end of the wire is bent up slightly and seems melted, so I'm quite sure I didn't brake removing the cap. I had also measured resistance with my dvm before removing the cap and got 0.0 Ohms reading.

There are clear numbers on the side (see pics) and in contrast to the Z Car Depot unit, the 3 holes on the bottom are a bit larger in diameter, there are 2 additional holes on the sides, and the hole on the plastic cap is also larger. All the holes in the can are screened.[mention=1115]Mark[/mention] Maras suggested that perhaps the small holes on the top of the Z Car Depot unit weren't allowing air to escape and impeding fluid from rushing into the can from below when submersed. Before disassembly I experimented by comparatively dunking both thermistors in a clear glass container full of water. You could see air bubbles escaping readily from the top of the original unit as it went in. Not so with the ZCD thermistor. I had to shake it and tap it so air would escape. This validates Mark Mara's observation and what you and Dave had suspected at times, that maybe fuel wasn't getting inside the can properly.

Please refer to one of my previous posts (# 82) for pics of the ZCD thermistor details.

 

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Dr. Dave,  Great photos of the failed original sensor. I did a little google searching on the internets for that part number (as I'm sure you did), and came up blank. I suspect that number is the part number for the ASSEMBLY, not just the thermistor. The thermistor itself is probably a small chicklet device with two leads on it. Just as a rough idea:

Looks like they soldered one lead to the wire embedded in the black plastic cap, and then they slid the thing together making sure the other lead poked out a hole in the metal can. Then they clipped the other lead off and soldered that other lead to the can. So in the end, you've got a one wired device with the other connection coming back through the chassis mount.

You pulled one lead out with the black plastic end cap, but there should be more to it. Either the rest of the device has turned to dust as a result of the heat, or may still be stuck down inside the can. You pic is too dark for me to see inside the can, but there is more still in there.

All that said, I think your analysis about the locations and sizes of the holes might bear some additional scrutiny. It seems unlikely to me that after being submerged in the fuel tank for hours, being shaken around by driving, that the air bubbles would not have worked themselves out of the ZCD sensor, but who knows. And if that sensor is sitting in a little air pocket, it could certainly behave exactly like the problem you're seeing.

Yarb, I don't know if it's just me, but I couldn't get your video to work. It downloaded, but it was a blank screen. Probably a problem on my end, but can you do youtube instead of hosting it here on the forum?

Maybe it's an iphone thing.  Here's my Windows 10 error message.  

couldn't get the video to work either