Gas Gauge

[Speed]

I installed a saddle tank from a '75 GMC pick up in the right side on my 1945 E model as an auxiliary tank. Well,now I have access to the other saddle tank,and all the fixin's,in good working condition. I'd like to use the wiring and tank sendig units from the '75 GMC with my Mack gas gauge,which is already 12 volt and works fine with the stock gas tank. What's the resistance value for these old truck gas gauges? If I remember right,the GM trucks are 30 ohm,but I haven't a clue on the . How do I check the compatability of the senders and the gauge without risk of letting the magic smoke out? I might use a hand operated tank valve so I can keep the cab tank connected;that'd give me 300 to 420 miles range,depending on load and road speed, (I'm not sure the word speed should even be used in this sentence. ) but still would like to use the stock gas gauge. Hope someone out there can help!

Speed

[Greg Rider]

DON'T If you hook that sender to your gauge you will smoke the gauge.The factory gauge is made by Stewart-Warner and has different resistance.I think it is 330 to 10 Ohms.Sorry it has been a while for me on here but I was busy working my main job and 2 part time jobs.The crappy thing is that I got laid off AGAIN! NAPA has a sending unit that is the correct ohms and is adjustable for tank depth.Check JC Whitney also. PS: I just put new tail-light panels on Faith with LED lights and aluminum diamond plate mudflap brackets and a matching center panel also!!! Plus my 4" chrome stacks came in Thursday so now I have to get those babies mounted.

[Speed]

DON'T If you hook that sender to your gauge you will smoke the gauge.The factory gauge is made by Stewart-Warner and has different resistance.I think it is 330 to 10 Ohms.Sorry it has been a while for me on here but I was busy working my main job and 2 part time jobs.The crappy thing is that I got laid off AGAIN! NAPA has a sending unit that is the correct ohms and is adjustable for tank depth.Check JC Whitney also. PS: I just put new tail-light panels on Faith with LED lights and aluminum diamond plate mudflap brackets and a matching center panel also!!! Plus my 4" chrome stacks came in Thursday so now I have to get those babies mounted.

Cool,Greg! Hope you'll post a couple of pics when you get the stacks on. Sorry to hear about the layoff though. I know how it feels-I've been laid off more than most people's whole families. Hopefully it will only be temporary and won't tank your finances.

Hey-on these saddle tanks that pull from the top,if I coupled 'em both together through a "T",would the truck still draw from the tanks evenly,or would I have to build a transfer pipe between 'em down at the bottom? I'm thinking if I could do that,I could run those as the main tank and use the original tank as a reserve,and use one NAPA sender;that way,I'd have both the main tank(s) and the tank covered,and would be able to run it all with the Chevy switch and valve. (I can just see it-get on a stretch of road that tilts,and even though I had a quarter tank,the uphill pick up would suck air and I'd still be outta gas...) Well,thanks for the info;I knew somebody'd come along who knew about the gauge resistance. I'll probably figure a way to run all three tanks the right way.

Speed

[Greg Rider]

I would run a small transfer line between them. That way only one tank needs to have the sending unit and it would read accurately. A small line like 5/16 or 3/8 is plenty. Just be sure to protect it well. Most are put in a piece of channel. You don't need some debris thrown from a front tire ripping the line out . I started to mount the stacks but found out that my adapters from 3" to 4" don't fit!!!! Aparantly 4" is not the same as 4" to some people . I spent 1 hr polishing and waxing the stacks,clamps,and rain caps. I used high temp paint on the rest of the parts. I will get pics as soon as I can .

[Rob]

Aparantly 4" is not the same as 4" to some people . .

Hi Greg, sometimes you have to be clear with the parts supplier if you need outer, or inner diameter when ordering pipe. I've seen this several times in the past.

A lot of folks don't think to ask, especially if they are looking in a catalog for a specific application, but when custom building something, it always seems to need to be addressed.

That A-30 will look sharp with chrome stacks. I think four inch is perfect.

Rob

[Rob]

I installed a saddle tank from a '75 GMC pick up in the right side on my 1945 E model as an auxiliary tank. Well,now I have access to the other saddle tank,and all the fixin's,in good working condition. I'd like to use the wiring and tank sendig units from the '75 GMC with my Mack gas gauge,which is already 12 volt and works fine with the stock gas tank. What's the resistance value for these old truck gas gauges? If I remember right,the GM trucks are 30 ohm,but I haven't a clue on the . How do I check the compatability of the senders and the gauge without risk of letting the magic smoke out? I might use a hand operated tank valve so I can keep the cab tank connected;that'd give me 300 to 420 miles range,depending on load and road speed, (I'm not sure the word speed should even be used in this sentence. ) but still would like to use the stock gas gauge. Hope someone out there can help!

Speed

You could take the wires loose from the back of the gauge, wire in a 0-500 ohm potentiometer in series and set at maximum resistance, and then connect a battery into the circuit. You would then place across the terminals of potentiometer, (use a digital meter as the impededance is about 10 megohm) and slowly reduce the circuit resistance watching the needle deflection of the fuel gauge. When you have a indication of "full" by the needle, you can read your multimeter and this will be the approximate resistance of your gauge. These things are not built precise enough to be exactly 330 ohms, (for instance) but will be within 15% for full scale deflection.

Rob

[Speed]

Thanks Rob;

I'll give this a go as soon as I have room to bring the home and work on it. My Dad was an electronics wizard,and tried to teach me what he knew,but since it wasn't about engines and wheels it just didn't interest me. Now I wish I'd paid attention,but it's too late.

Speed