Rotus Fuel Sender

[tgentry]

The fuel gauge on my Rotus Eight is always on E. Since sender to ground is 0 ohms I'm guessing the sender is bad, possibly a float not floating. 

 

Does anyone know how to access the sending unit? Or what sending unit they used?

[MV8]

Remove the eight roll bar bolts and fuel filler cap. The top cover should lift off. It may hinge at the carpet lining the boot so it won't need to be cut. Should be a 17 gallon tank with no expansion space (don't fill to the brim).

 

You can determine the correct sender using a 500 ohm potentiometer (like car radios used to have for volume control) for about $3. Connect the pot between ground and the gauge, apply power to the gauge, then rotate the pot until it shows empty. Check the pot resistance with a dvm. Repeat for full indication. Let me know if you need a link to the POTs on amazon.

 

You can convert to a marine stainless tube design. These come in many ohm configs, flange mount to the top of the tank, and are also selected based on the longest tube that will fit in the tank (for accuracy when the tank is low). You can swap the gauge as well. Should be a standard 2 inch hole.

[MV8]

It looks like VDO are typically 10-184 ohm. Most universal senders are 0-190 ohm and can be tweaked to work with a VDO (so as not to go past full or empty indication on the gauge). It is also possible that all you need is a new float, to solder a cracked brass float, or the old one fell off the arm (they often snap on).

 

A marine stainless reed switch sender (must select the right length) is around $50 for a VDO gauge and around $20 for one calibrated for a 0-190 ohm gauge. A traditional swinging arm sender for VDO is around $25.

[Marek]

As the Rotus tank is directly behind the seat back, the pump, sender, and filler are readily accessible under a vinyl cover (not shown here). The vinyl is fixed with an aluminum trim attached with screws.

 

[MV8]

Marek, for comparison, here is his tank cover with carpet. Perhaps there is rubber underneath?

Edited November 13, 2025 by MV8

[Marek]

Yes, that car has an original roll bar and is a simpler trim using carpet.  But remove that carpet and the sender and pump will be mounted from the top.

 

The 16.5 gallon tank is horseshoe shaped where the arms tilt towards the front of the car; so that the tank sits above and straddles the rear axle but the ends of the arms extend in front of the axle.  There is a balance tube running under the driveshaft to connect the two arms and the pump reaches down into one arm.  Unfortunately I don't seem to have taken a picture of the tank when mine was out of the car.  But the sender looks like this:

 

[MV8]

I found a good pic of the bottom of the tank with the balance tube.

[tgentry]

I was just under the changing diff oil. BTW, the T-5 transmission was a little tough.

[tgentry]

9 hours ago, MV8 said:

Marek, for comparison, here is his tank cover with carpet. Perhaps there is rubber underneath?

That looks like mine, except I have the simple single hoop rollbar.