dmorales-bello

Good morning Cap'n O, I could not manage to snap a picture inside the can that would show what was in there with artificial lighting. With the help of some diffuse sunlight "by George I've got it". (movie reference. Trying to fit in! [emoji851]). The only thing that's in the can is a fragment of the broken wire about 3/4" long sticking straight up from the bottom where it is still attached to a point of solder. That's it. Is there a chance some other component of the thermistor is embedded within the plastic cap? Hope this helps Sent from my SM-N950U using Tapatalk

Yarb's thermistor looks exactly the same as my original '78 unit. Sent from my SM-N950U using Tapatalk

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. Sent from my SM-N950U using Tapatalk

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? Sent from my SM-N950U using Tapatalk

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. Sent from my SM-N950U using Tapatalk

2000 BC? Sent from my SM-N950U using Tapatalk

Good morning CO! I actually measured the distance from the edge of the tank where the fuel sender fitting is to the fuel surface at half tank (5"). The thermistor is 10" from the sender base so it must be sitting 5" beneath the fuel surface at half tank. The holes in the ZC Depot thermistor are smaller than those on my original unit. Perhaps they would allow trapped air to escape and fuel to flow in easier if they were twice the diameter (more similar to stock). However, when I ran the bench tests it seemed like water flowed in and out unrestricted. My original thermistor does not work (registers no resistance) and I would have no problem sending it to you for post mortem study. Sent from my SM-N950U using Tapatalk

Thanks for the video once again, Dave. I would think the pot could be used with the lower resistance bulbs. If I were to use it with the higher resistance bulbs they would probably never light up even with the thermistor out of the gas, correct? Sent from my SM-N950U using Tapatalk

I received 5 bulbs with different ratings yesterday. They do not show the Volt or Amp rating on them as other bulbs do. Therefore I decided to identify them by the measuring each bulb's resistance on the bench (cold resistance?). Once again I ran the car with the original 12V 3.4 amp bulb in the "fuel" light housing with the tank at about half full. Once again that bulb lit brightly after about 25 minutes. With the car still running I swapped the stock bulb for each one of the new bulbs. All of them illuminated immediately although dimly. The difference lies in how dimly each one lit up. In general, the bulbs with the highest cold resistance were dimmest. I was also measuring voltage at the bulb harness for each bulb. That voltage varied when each new bulb was placed in the socket but stabilized within a minute or less. I identified the bulbs from #1 to #6 in order of decreasing resistance. Bulb 1 being the new bulb with the highest resistance and bulb 6 being the stock bulb which had the lowest resistance. RESULTS : BULB 1: 19.8 Ohms, weakest glow, stable at 2.9 V. BULB 2: 12.7 Ohms, weak glow, stable at 3.1 V. BULB 3: 11.5 Ohms, very weak glow, stable at 4.0 V. BULB 4: 11.4 Ohms, slightly brighter glow, stable at 3.3 V. BULB 5: 6.3 Ohms, brighter glow, stable at 5.8 V. BULB 6: 3.8 Ohms, very bright, stable at 7.7 V. The glow from bulbs 1, 2 and 3 can barely be seen through the red lens of the housing even inside the darkened cockpit (I was outside at 9pm. Wife thinks I'm going insane! ). With the roof light on, you can't detect light through the lens. The glow from bulbs 4 and 5 can be readily seen through the red lens in the dark (5 more than 4) and are somewhat visible with the roof light on. Bulb 6 (stock) is very blatantly visible in the dark and quite bright with the roof light on. I ruled out the stock bulb (6) , and the new bulbs at each extreme (1 and 5) for being too dim or too bright. Bulbs 2, 3 and 4 are dim enough that are very hard to be seen through the lens, day or night. But should be brighter and visible when the thermistor is above fuel and it's resistance drops (I think). I placed bulb 3 in the housing and closed everything up. I will run the tank dry and see how the light behaves. I will have bulb 2 and 4 as alternatives. I know my "report" is not very technically correct but it kinda gives me options. Sent from my SM-N950U using Tapatalk

Got it. Thanks again. I hope CO can confirm values. Sent from my SM-N950U using Tapatalk

Excellent explanation! Got it, thanks! BTW, the bulbs will arrive this afternoon and I'm ready to test them also. Sent from my SM-N950U using Tapatalk

Ok, so what's the practical application in this case? Sent from my SM-N950U using Tapatalk

Could you explain this a little further? Sent from my SM-N950U using Tapatalk

I've not contacted the vendor waiting for us to come up with a viable solution. I did ask him for a couple of weeks time to try out the second unit he sent but that was before I realized it was having the same issue as the first unit I got from him. He seems very amicable so I don't expect anything negative but... You never know. Sent from my SM-N950U using Tapatalk

Wouldn't you have to have the thermistor receiving power in order for it to heat up enough to drop the resistance even lower? Sent from my SM-N950U using Tapatalk

I will try the bulbs when I get them at the end of this week and hope at least one of them works. If not I'll hit you up for a rheostat as a final attempt. I'm very thankful for all your help Dave, plus all the insight from @captainobvoius and the others. I'm still holding on to hope that this "little light problem" won't lick the crowd knowledge base in this amazing forum. Sent from my SM-N950U using Tapatalk

So I experimented by measuring resistance in the thermistor while exposing it to different temperatures. Exposed to 78 degree "Florida early morning" ambient air, the reading was 2.2K Ohms. When introduced into 100 degree water (as I imagine the temperature of fuel could reach during driving in 95 degree weather for a while? ) the reading dropped to 1.44K Ohms. Finally, raising the water temperature to 124 degrees the reading dropped further to 0.94K Ohms. That would seem to show that the thermistor is responding to the temperature around it, be it immersed in fluid or dry. My limited knowledge of electronics however, doesn't allow me to infer if those values are consistent with normal function as intended for this particular application. Sent from my SM-N950U using Tapatalk

There are holes on the top and bottom of the thermistor. After submerging it in water (another experiment I just performed and will post in a minute) the can fills with fluid which I can expel from the bottom holes by blowing through the top holes. So the unit is not clogged and fluid will flow in and out of it unobstructed. Sent from my SM-N950U using Tapatalk

Same back probe test but with the car engine running: 14.5V without the bulb 34.7mV with the bulb Sent from my SM-N950U using Tapatalk

Back probe test results with key in the "ON" position : 12.29 Volts without the bulb 18.9mV with the bulb Sent from my SM-N950U using Tapatalk

Got it Dave, thanks. I'll try the test and call you if I get stuck. Sent from my SM-N950U using Tapatalk

The malfunction is exactly as you describe it. As far as testing voltage at the lamp plug, sounds good and I think I understand it. Do you still want me to try all the different higher resistance bulbs with simple 25 minute runs to see which ones go on with a full tank? Sent from my SM-N950U using Tapatalk

I bench tested the resistance of my sending unit with 2 different DVMs and got very similar results: 2.99k ohms and 2.98k ohms. Sent from my SM-N950U using Tapatalk

My bulb plug has a 5 inch long harness that plugs into another harness above the HVAC vent. Is that where you want me to check? I have a duplicate sender out on my workbench. Is there something I can do with that sender that will provide the info you need instead?

I have no problem with the temporary digression from the original topic. (I do wish I had a better understanding of electronics). I consider it an "intermezzo" while I wait on my new bulbs to arrive and I can proceed with my relatively simple experiment. Sent from my SM-N950U using Tapatalk