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Aftermarket fuel gauge with stock e30 sending unit


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To the E30 teams running:


Anyone using an aftermarket fuel gauge with a stock BMW sending unit?


The stock unit is full/empty 0/60 ohms which is backwards of every fuel gauge I can find.  Autometer makes a programmable gauge but they are, at least, double the cost of a regular gauge.


Anyone using the stock fuel gauge as a standalone gauge?  Looking through the wiring schematic I don't see why it wouldn't be possible but curious if anyone is doing it.

page 63.



I am building an e30 (personal not Chump) and I will be replacing all the stock gauges with aftermarket.  I was going to ditch the factory gauges and make a replacement panel with the new gauges. I can gut the old housing and mount the gauges in it to retain the function of the factory fuel gauge if it will work on it's own. 




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How are you going to get an aftermarket gauge that combines the inputs from 2 different fuel level sensors? 


Not all of the e30's have two level senders.  The 84-87 E30s had a 14.5 gallon tank with two fuel pumps (internal/external) and a tube running under the driveshaft connecting the two halves of the tank. In 88 BMW started installing 16 gallon tanks with two senders and one fuel pump (internal).


Mine is an 86, so it had the 14.5 gallon tank, two pumps, and goofy cross over tube.  I replaced the tank with a 16 gallon tank and instead of two sending units, I used the extra hole to hang another pump.  The second pump is run from the OEM wiring and will scavenge fuel from one side to the other in addition to the "siphon"
 system that the tank has built in.  The "main" pump has been replaced with a Walbro and the hanger still has the stock sending unit. 

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What about this gauge, but add a 4.7 ohm resistor in series? That should get it in the ballpark.




Nice find!  

I looked all through Summit last night and all I came up with was stuff like this. 


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So does it show full until it's really at half full.  It other words the right side stays full until the left side is empty then it starts to burn the right side? 


No,  the e30 tanks stretch across the width of the car and are under the backseat.  The drive shaft running through the middle creates a little rise in the middle of the tank that separates the two lower halves of the tank. The portion of the tank closer to the top is open and fuel can freely flow from one side to the other.   BM1B_TOP_P04.jpg    through the 

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It will work on its own. You just need to remove the 2 nuts holding it in which are the + and - references (from memory so don't quote me).While building the #14 e23 I had the cluster apart and had planned to just wire in the gas gauge separate rather than go through all the wiring. I ran out of time, but did manage to do this. Warning lights are for water temp, oil pressure and oil temp (all being remote gauges).


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  • 2 weeks later...

A little follow up. 

I purchased the gauge that Cabot recommended and did a little bench testing.  Not that any of this is a surprise but I thought I would share the results of the bench test,


A standard e30 sending unit should be at 0 ohm when full and 60 ohms empty -  the gauge I purchased is 10-65 ohm full and empty respectively.  

With the help of an electrical buddy, we used a 1000ohm pot to vary the resistance being sent to the gauge between 0-60 to mimic the factory sending unit.


At 0 ohms the gauge had no problem reading full.  At 60 ohm the gauge read just above empty....which was expected but I wanted to know how far above "E".   Like Cabot recommended, a small resistor could be used to make it read all the way down but I think I'll leave it be.  Hopefully this all works as well in the car as it does on the bench. 





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  • 2 weeks later...
  • 2 years later...

Old thread, but just found this to help any e30 or other teams looking to use aftermarket fuel gauge with stock OEM sending units.



$60 on Ebay


Or this one from Speedway.com


$105, also provides signal for a fuel warning light.


I'm gonna order the Marshall unit, I'll post results soon...

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  • 2 years later...

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