Multiple fuel tanks with a single original gauge...

Every car has an electrical system. Here's the place to learn all about it.

Moderator: 2088 bob

Post Reply
Metal Twister
Posts: 89
Joined: Wed Oct 29, 2014 12:28 pm

Multiple fuel tanks with a single original gauge...

Post by Metal Twister » Mon Jun 20, 2016 8:21 pm

I'd like to build two and possibly three aux fuel tanks for the 181 Thing. Question is if I got three sending units all having the same ohm rating as the original gauge, can I then just use a 4 poll selector switch between the gauge and four poll switch? Seems like it should work . Obviously I'm not a spark chaser. Thanks in advance.

User avatar
Marc
Moderator
Posts: 23723
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Multiple fuel tanks with a single original gauge...

Post by Marc » Mon Jun 20, 2016 9:13 pm

Don't see any reason it shouldn't work. Any resistance that develops on the switch contacts would just make the gauge read slightly lower, and if you suspect that's a problem simply cycling the switch a few times will probably clean them.
Note that there are two families of fuel gauge systems used in VWs (thermal & balance coil) and you cannot mix the gauges and senders. Thing should have the thermal type as used in Beetles/Supers/LATE `Ghias.
Never leave the gauge sending wire grounded for long since that will smoke the gauge. OK to touch it to ground momentarily to confirm that the gauge sweeps past full but JUST for a few seconds.

You'll need senders that go from ~73Ω empty to ~10Ω full (zero at full would be a no-no as mentioned above). Most non-VW senders have higher resistance at full than at empty so your choices are pretty much limited to stock senders or ones that are intended for use with stock VW gauges, unless you change the gauge too.

Here's a good rundown on how both setups work if you're interested: http://www.speedyjim.net/htm/fuel_ga.htm

Metal Twister
Posts: 89
Joined: Wed Oct 29, 2014 12:28 pm

Re: Multiple fuel tanks with a single original gauge...

Post by Metal Twister » Mon Jun 20, 2016 10:16 pm

Thanks Marc for all the help here! I was thinking this was workable but electricity has me spooked just enough that I automatically try to get a seasoned opinion. That article is about the most complete I have seen. I know they used a few different sending units in the 181 Things so I had better figure out what is in it for sure. Thanks so much for well thought out answer.

User avatar
Marc
Moderator
Posts: 23723
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Multiple fuel tanks with a single original gauge...

Post by Marc » Mon Jun 20, 2016 10:56 pm

The best "natural" mechanic (much better than me, I must admit) I've known over the last 45 years was also frightened of electrical work. In my experience body-men are the worst, perhaps because they don't recognize their ignorance and press on regardless, reconnecting wiring incorrectly when reassembling a car and causing all sorts of mysterious symptoms. :evil: I suspect there's something about the artistic talent needed to be a good body & paint man that's just inconsistent with the logical thought processes required for electrical work.

If you've never had the benefit of training in basic electrical stuff, there's no shame in admitting you need assistance - it's better than trying to fake it and frying something ;)

Fortunately, if you can avoid working on fuel injection, there's very little advanced knowledge needed to work on our rather ancient cars. Having a basic understanding of how direct current circuits work will give you confidence, pick up a library book on the subject sometime - if you can grasp the concepts in the first quarter of the book you should be nearly fearless to tackle most electrical problems in an ACVW.

fall-apart-dave
Posts: 22
Joined: Sat Sep 15, 2007 8:32 am

Re: Multiple fuel tanks with a single original gauge...

Post by fall-apart-dave » Mon Sep 12, 2016 9:37 am

lol! As it happens, I'm an electronics / electrical engineer by trade, and I suck at bodywork... Maybe something in that!

Post Reply