I've searched, and found a few partial comments here and there, but has anyone ever found a definitive answer to the question of tank sender interchange?

I've an 80 SA, I need to know if I can farm later years' tank senders, since SA's are getting very rare in the local boneyards.

Also; I've never pulled the sender before; do I need a replacement gasket (does it have one) or do I need to use a specific sealant when re-installing?

Any advice greatly appreciated!

 

There is a rubber gasket that should be the same. As for SA vs FB, I couldn't tell you.

 

Some of the gaskets were cork. Oddly, the ohm values for the fuel senders are the same for the 1st and 2nd gens, whether they interchange is another question. That will depend on tank depth, and the 2nd gens vary between the S4/S5s with the S5s having 1" more depth, 10" vs, 9". The bolt pattern where the sender mounts will be another consideration. You might check with Mazdatrix to see if the SA/FB senders have the same part #.

On Sgt Foxes website, there are parts catalogs. I will take some digging, but you can find the part #s for both the SA and FB senders. If they match, you can use either one, if not, get the SA one.

When I installed the Autometer gauges, I did extensive research and figured out a way to adapt one of their senders to work with my S3 tank and the Autometer fuel gauge. To make sure I got it right, or at least close, I cut a junk tank in half to test fit and calibrate the fuel sender. My gauge reads a hair off as it stays on full longer than a stock sender would and when it reads empty, I have at least 4 gallons of fuel left. Overall, I'm happy with the results and buying the gauge and sender was cheaper than buying an oem sender.

 

DD - uses rubber gasket - still available from Mazda (the gasket, not the sender), just bought some myself...
Sender interchanges only with 79 SA AFAIK
Stu Aull
80GS
Alaska

 

Bueno - thanks for the info.

I may pull a 81 sender at the JY just to see what diffs there may be. Might be able to bastardize bits to work, too.

Need to pull mine first, see what's up with it, but not having broached the tank before, I wanted to make sure I could re-seal it after. It's reading very high resistance (about 200kohms) at the tank connector, so it's got something not right. Used to work. Probably dissolved, or something.

I have an allergy to explosions in my garage, unless I plan them. Whole idea of electricals submerged in fuel makes me itch.

 

Mine is reading over 1k as well. I need to take it out and move it through its range while taking resistance readings. Maybe there's a piece of corrosion blocking the contact patch?

 

I'll be interested to see how it goes together - - never seen one "in the flesh" before. Probably one of about 25 parts on the car that I've never had to remove.

 

My guess is that it will not work correctly. Mazdatrix shows 81-83 and 84-85 for their senders (nothing for 79/80). The tank is smaller on the SAs (more shallow). I imagine that the sender will fit, but the float willeither hit prematurely on the top of the tank or on the bottom. If this is the case, weither the gauge will never read F or never drop to E. I'm pretty sure the ohm range is correct (have to check FSM to verify). I just believe that there might not be enough mechanical range.

Not sure if it is the same on the SAs, but on the FBs you remove the driver rear tire and the plastic rear well piece to gain access to the sender. Unplug the sender and remove the 6 screws (screws can be hard to remove due to rust/corrosion). You might need some PB Blaster and some needle-nose vicegrips to get them out. You can get new screws from the hardware store if yours get beat up. They are 4mmx 0.7mm pitch, 10mm threaded length. Try to get cap hex head (allen) to make them easier to remove in the future.

As for the 81-83 vs. 84-85 senders, they are interchangable with a change to the electrical connection. The 81-83 is a two-terminal connector and the 84-85 has three terminals. The extra terminal on the S3 cars is for the low fuel warning light.

 

Interesting. I located the sender for testing last night, same position as you described (Driver's rear wheel, behind the panel.) It has a two-prong male connector on it, looks like --|

If the only difference is tank depth, then it might be possible to just shorten the arm length, depending on how it's assembled.

Will probably be the weekend before I can explore more. Busy week of other things coming up.

 

Most members are too young to know how old radio tuners were built. One could order a kit through Popular Science and build and build their own radio. The tuner was a bar wrapped with wire and a contact was moved along the winding to tune in a station. The sending unit works on the same principle, the more wire that the current passes through, the more resistance, (ohms), is read. As a side note, the gauge has windings too. If the white wires of the winding are brown or black, the gauge is usually toast. Same goes for the oil pressure gauge.

That pickup moving across the fine wires of the sender eventually wears through and breaks the wires. This is why sometimes one can get a partial reading on the fuel gauge, but not the full sweep of the needle. I had one that wasn't working correctly, so I took it apart and found a couple of broken spots in the winding. This made the needle/fuel level reading erratic. On the S3s that have the low fuel light, that is not affected by broken wires in the winding since it is a separate sender.

 

More good info.

As one old fart to another (and a Heathkit/Radio Shack/Pop. Electronics geek since I was eight) I get you, Sir: The sender is a rheostat.

Gauge is a bimetallic thermometer with a heating element around it. Sender rheostat in series with the heating element controls total current through both, which controls the temperature read by the gauge. Thermal-drive meters were used because their slow response damped down the wave action of fuel in the tank, eliminating gauge bounce.

Amazes me that such can be used in a fuel/air environment without concern of sparks, but they must use a make-before-break design (wiper of the rheostat touches several turns, so contact is never actually broken) , & carefully limited max current. Obviously, it works just fine as a design.

Is the rheostat part of the sender in a sealed enclosure, or just open to the tank?

 

Basically open in the tank, sitting inside a tin case that doesn't seal. Sender is very basic and simple. If there's a way to rewind the wire, they might be able to be repaired.

 

Or might be able to use the rheostat part from a FB to rebuild an SA sender? I knowwhere to find a half-dozen junked FB's, but SA's are getting to be rare to see.

 

Could be. Might be as simple as removing the arm/float from your SA sender and attaching it to the FB sender.

 

oddly ive had great luck with those BS fuel system cleaners fixing the gas gauge.

 

Mine just needed to be in a gas fume atmosphere and it started sort of working again. It was reading about 1k before and now reads about 40 ohms at about a quarter tank (I think - not sure of actual level because my gas guage doesn't work.

 

The mazda dealer hereabouts is ordering me a couple of the appropriate gaskets ($4.17 each), and it looks like Saturday will invlove a dodge to the boneyards, for some "experimenting" material. And possibly the one SA I knew of may still be out there.

 

the FC sending unit doesnt "drop" in but it can easily be modified to fit. i did this on my SE. My buddy gave me his old sending unit and i just used my old plate from the FB that the sensor mounted on and remounted the FCs sensor on it. after doing that i trimmed and bent the bar piece that the floats on accordingly to the FBs original bar. worked like a charm

 

Sadly, the one SA I knew of in the local yard has apparently gone on to a date with the crusher. Snoozed, losed.

In another yard, I visited an 85 that I knew was tthere, and got the sender from it for experimentation purposes. It has the "low fuel" dipping sensor that I don't need, but it looks like I can salvage the wound-resistor portion from it easily enough, should the one in my car prove bad.

I'm not pulling mine til the new gaskets are in hand, though, as I don't want to leave it out longer than needful - - my tank still has gas in it.

Interestingly enough, the 85 I farmed had a near perfect set of rear interior fender covers... in black, and from an SA. Apparently, the previous owner was doing some interior conversion (the original interior was brown).

So the trip was not a total bust, as my current interior rear covers are OK, but were not originally black, and the vinyl paint is peeling in spots.

Scored some good hood rear-edge weatherstrip. too.

 

I've got a bunch of pictures that will show up soon in a longer post, but here's the skinny;

I was able to successfully transplant the wire-wrapped resistor element from the 1985 sending unit into my 1980 sender assembly. My original unit is now fully functional.

It was not real easy, as these things are NOT made to be taken apart (they are swaged together), but if you are real careful, you can desolder the terminal, swing the pickup arm out of the way, and carefully jimmy one element out, and the other will fit - - they are mechanically and electrically identical.

So, SA senders can be repaired using parts from later units. Don't toss them out!

More later, when I'm not half asleep.

 

pics? then archive?!?!?!?!

 

I ended up writing it up as a separate thread, Rolfs... and I got archived!

I'm so proud...!

https://www.rx7club.com/showthread.p...85#post8554085