Moderated Discussion Areas
  ContinuousWave: Small Boat Electrical
  Fuel Tank Level Sender: Electrical

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Fuel Tank Level Sender: Electrical
jimh posted 10-19-2005 01:54 PM ET (US)   Profile for jimh   Send Email to jimh  
[UPDATE SEPETEMBER 2016: I have reviewed this article and updated URL's which changed, where possible.--jimh]

If your Boston Whaler has an electrical fuel gauge sender, you might consider replacing it with a new sender from CENTROID PRODUCTS of Edgewater, Florida. (They're just down the road a bit from Boston Whaler's factory!)

The CENTROID PRODUCTS sender is designed with no moving parts. It senses the fuel tank level measuring the capacitance between two concentric tubes which are immersed into the tank. As the liquid level rises, the capacitance between the tubes is affected, and this is translated into a signal which can be connected to a standard fuel level gauge (a milliamp meter, typically). The electronics are encapsulated in epoxy and should be maintenance-free.

In addition to no moving parts, the sensor has another benefit: it can detect water in your fuel! The presence of water apparently has quite an effect on the capcitance, causing the indicator to significantly change its response.

The sender is fabricated with the standard five-hole bolt pattern typically found on Florida Marine Tanks as seen in Boston Whaler boats. When installing the sender, the length of the tubes is custom fit to your tank. You use a tubing cutter to trim them to the right length depending on the depth of your tank.

Each unit is calibrated to a particular installation. The empty calibration can be done before installing the unit into the tank. The full calibration is set once you top off the tank.

The claimed advantage of this sender include a reduction in gauge bouncing when fuel is sloshing around. The sender is compatible with most electric fuel gauge meters, but some VDO-brand meters need a special model.

For more information see the CENTROID PRODUCTS website:

I have not tried one of these myself, but I like the concept of no moving parts and individual calibration.

jimh posted 10-19-2005 01:59 PM ET (US)     Profile for jimh  Send Email to jimh     
Detailed price and application information is found in this document:

It looks like a common sender unit would cost about $50.

Liteamorn posted 10-19-2005 03:34 PM ET (US)     Profile for Liteamorn  Send Email to Liteamorn     
This sounds like a GREAT new product, I work in the oil industry and the technology is there for a water sensing unit. When I mesure how much gas or oil is in a tank (with an electronic tool called an "MMC") we just lower the sensor bob all the way to the bottom of the tank and it reads water, I wondered how long it was going to take for this to happen.
jimh posted 10-20-2005 11:25 PM ET (US)     Profile for jimh  Send Email to jimh     
I have the boat home tonight and I was out with a flashlight looking at the tank fitting for the level gauge (in the 40-degree evening air). It is NOT a five-hole SAE standard flange, and I wonder now if these level senders can be fitted to the normal classic Boston Whaler fuel tank with mechanical sender. At first glance it does not look like it.
daverdla posted 10-21-2005 08:06 AM ET (US)     Profile for daverdla  Send Email to daverdla     
Here's another neat multitank solution I've been considering for our trawler:
[DEAD LINK has been deleted]
The centroid is proabably a better solution because it will convert the measured liquid height to volume even for odd shaped tanks. Unfortunately, it won't do holding tanks. I need to monitor two fuel tanks, two water tanks and one holding tank.
Jerry Townsend posted 10-21-2005 11:46 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Dave - It looks like the unit you linked is a differential pressure device - special extruded nylon tubing, That would also explain the different calibration required for each fluid.

You mention the Centroid device will not work on holding tanks - why? If it is in their literature, I missed it. I would think that it would not make any difference - as it is simply looking at a capacitance measurement.

Jimh - If the diameter of the mounting plate is large enough, one could drill 4 new holes on the hole pattern of the existing tank to match the existing 5 hole pattern.

I like the capacitor indication device - should work like a dream - and be accurate, linear and trouble free. I would even like to put one in my pickup - so I will get hold of that company and explore that one with them too. --- Jerry/Idaho

daverdla posted 10-22-2005 04:59 PM ET (US)     Profile for daverdla  Send Email to daverdla     
Somewhere on their website they state that they no longer do holding tanks. Probably too many failures from getting clogged with toilet paper or worse. Its a shame really because the centroid would be a better solution for me. I do like the simplicity of the tank tender but looking up gallons/inch on a chart can't beat reading the volume on the centroid.

A quick search turned up another solution:
It doesn't look like it can be calibrated for odd shaped tanks.


jimh posted 10-24-2005 10:21 AM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the bolt pattern: it appears the Florida Marine Tanks in Boston Whaler boats with MECHANICAL fuel level indicators use a different bolt pattern (four holes) than the SAE five-hold standard. Perhaps the Boston Whaler boats which have ELECTRICAL senders use the five-hole pattern.

Comments from owners of Boston Whaler boats with electrical fuel senders are welcome. Does your boat have the SAE five-hole pattern on the sender port?

dongordon posted 11-21-2005 12:55 PM ET (US)     Profile for dongordon  Send Email to dongordon     
My 18' Guardian has an SAE five screw sender cap with a red wire connecting to the center of the cap plate and a black wire snapping onto a clip on he top edge of the cap. My fuel gauge has a logo with a single letter Q and a line beneath the Q. Does anyone recogize that trademark? Does any one know the ohm reading on the 5 hole sending reading? Thank you.
Buckda posted 11-22-2005 05:47 PM ET (US)     Profile for Buckda  Send Email to Buckda     
How about a source for a replacement MECHANICAL sender for the OEM Whaler tanks, built by Florida Marine Tanks.

We have sources in the OEM section for the Tanks, and the gauge, but not the sender.

In the attempt to replace my gauge, I've broken a very small screw head off, and will need to replace the entire sender unit.


JOHN W MAYO posted 11-22-2005 10:07 PM ET (US)     Profile for JOHN W MAYO    

I think this may be the source for the possible the original??.......fuel guage. Someome gave me the link a long time ago.....go there and you can see the pictures, etc

4 Bolt Hole Fuel Gauge

Jr. 4 bolt hole fuel gauge
(item pictured has fixed length)

* Top or side mount
* Direct read or direct read with remote transmitter
* Buna-N gasket & hardware included
* Adjustable models available for tank depths of 5" to 24"and risers less than 1 1/2"
* Fixed length gauges are available for larger tanks upon request.

Sr. 4 bolt hole fuel gauge
(item pictured has fixed length)

* Direct read or direct read with remote transmitter
* Buna-N gasket & hardware included
* Adjustable models for tank depths of 5" to 24" and risers less than 1 1/2"
* Fixed length gauges are available for larger tanks upon request.

These gauges are widely used to measure levels of fuels, hydraulic fluids,
refrigerants, lube oils. Optional models available for use in cryogenic products
and pressures up to 500 PSIG.

e-Components International, Inc......
307 Spring Hill Road
Lancaster, Virginia 22503
804-462-5679 - 1-800-640-1556
Fax 804-462-0556-------

Buckda posted 11-23-2005 10:42 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Thanks John-
I didn't see that on their site orignally. I ordered a replacement dial from them earlier this fall when I was preparing for this project.

Great people out there at E-Components.

I'll give them another call.

JimH -
Sorry to slightly de-rail this thread.


JOHN W MAYO posted 11-25-2005 08:55 AM ET (US)     Profile for JOHN W MAYO    
The 4-hole type seem hard to find for the older Whaler's. Forget West M, Boaters World, etc......this is the only place I have found them. I would confirm the dimentions, bolt pattern, etc before order
swist posted 11-25-2005 09:19 AM ET (US)     Profile for swist  Send Email to swist     
It is encouraging that some progress is being made in this area. The old pivoting-arm-on-a-variable-resistor seems to be the only fuel gauge sending technology we have ever had - and they are pretty much all crap - they can't take all the movement in a small boat, they get hung up on sides and baffles, and they are generally unreliable. This has been one case (rare in boating!) that you can't spend the money you would like to for a better product.
jimh posted 05-31-2006 12:26 AM ET (US)     Profile for jimh  Send Email to jimh     
If anyone has ordered one of these CENTROID PRODUCTS fuel level sensors, I would be very interested to hear a report on how it worked for you.
DjPro posted 05-31-2006 01:35 PM ET (US)     Profile for DjPro  Send Email to DjPro     
[Gave a narrative of how a different product which was not a direct indicating fuel tank level sensor could be used. This article has been moved to a separate discussion on indirect fuel tank level measurement devices.--jimh]
jimh posted 05-31-2006 04:58 PM ET (US)     Profile for jimh  Send Email to jimh     
There are many prior discussion whose topics are other fuel tank measuring systems which do not employ direct level indicators. Such devices attempt to compute the level of fuel in a tank via an indirect measurement, typically by deducing tank level from fuel flow measurement. The topic of this discussion is electronic tank level sensors. These devices register the tank level via direct measurement. The particular device under discussion uses an innovative technique to directly measure the tank level. Again, if people have installed the innovative tank level sensor made by CENTROID PRODUCTS that is the topic of this discussion, please let me know. Thanks.
jimh posted 12-30-2009 11:29 AM ET (US)     Profile for jimh  Send Email to jimh     
Electronically-operated electrical remote fuel tank level senders similar to the CENTROID models mentioned above are also made by WEMA. Information is available on their website at:

These senders apparently provide the equivalent to the more or less standard 240 to 30 ohm variable resistor or rheostat sensor used in traditional mechanical senders that control current flow through a remote gauge powered from the 12-volt battery. Like the CENTROID they appear to be electronic in their operation, that is, they really don't actually have a simple rheostat type device in them but simulate it using electronics. Unlike the CENTROID there is a moving part in the WEMA sensor, a float collar that rides up and down on a central tube. There does not appear to be any direct mechanical linkage from the float collar to a potentiometer, so the electronic nature of the product is inferred.

The WEMA sensor model SSS or SSL uses a five bolt SAE mounting pattern with a 2.125-inch bolt circle. As discussed above, this may be inappropriate for direct adaptation to an existing mechanical level sender port on a classic Boston Whaler fuel tank, however it appears to be the otherwise standard configuration for electrical-electronic senders of this type.

jimh posted 02-05-2010 08:18 AM ET (US)     Profile for jimh  Send Email to jimh     
An electronic fuel tank level sender gauge suitable for marine fuel tanks is made by SSI TECHNOLOGIES, INC., of Janesville, Wisconsin. Their Fluid -Trac® two-wire liquid level sensor with resistor emulation can be used to replace the conventional mechanically linked standard 30-240 ohm resistive float senders often seen in small boat fuel tanks. The device is certified by the American Boat and Yacht Council (ABYC). It has no moving parts and does not protrude into the fuel tank. The device operates with digital signal processing and includes filtering to reduce the influence of fuel sloshing on the output signal. The device also appears to be able to compensate for fuel level measurements in tanks with unusual shapes. These digital algorithms are set at the factory and are not user adjustable.

The Fluid-Trac sensor appears to operate using ultrasonic distance measurement. It measures the distance from the sensor to the top of the liquid in the tank. The device is claimed to have a fundamental accuracy of two-percent. Variations in the distance from sensor to fuel from sloshing are treated as noise and are filtered out. The response time can be set (by the factory) to as long as a four-minute average in situations where there is high sloshing.

The mounting of the sensor can be accomplished with either the standard SAE five bolt pattern or with a 1 and 3/16-inch threaded mounting.

More information is available from SSI TECHNOLOGIES:

jimh posted 02-05-2010 08:23 AM ET (US)     Profile for jimh  Send Email to jimh     
The Fluid-Trac sensor costs approximately $95. It can be ordered from U.S. Marine Products. products_id=298

as well as from other distributors .

meridian posted 10-29-2010 03:47 PM ET (US)     Profile for meridian  Send Email to meridian     
I brought this back to see if anyone has first hand experience with the the SSI Fluid-Trac, WEMA SSS/SSL, or Centroid units?

I want to keep my 2-wire 30-240 ohm gauge. Since my tanks is a isosceles trapezoid, I need a unit I can calibrate. I talked to SSI and they can produce a calibrated unit for a couple of hundred dollars, not an off the shelf unit.

jimh posted 10-29-2010 03:59 PM ET (US)     Profile for jimh  Send Email to jimh     
Terry--May I suggest the following:

--use either the conventional resistive sender you have, or
--use one of the electronic equivalent senders;
--use the I-Command fuel manager gauge;
--use the five-point fuel tank level calibration method for the I-Command fuel manager to teach the fuel manager the shape of your fuel tank

I think in this manner you could have a reasonably accurate fuel tank level gauge from the I-Command.

meridian posted 10-29-2010 09:41 PM ET (US)     Profile for meridian  Send Email to meridian     
I-Command will be a challenge with my 1992 Yamaha
jimh posted 10-29-2010 10:15 PM ET (US)     Profile for jimh  Send Email to jimh     
Oh! I forgot you recently sold your E-TEC motor.
jimh posted 10-30-2010 12:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Terry--Since you have a Boston Whaler boat with an electrical fuel tank level sender, please inform us about the bolt pattern arrangement. Is the sender you have configured with the SAE five-bolt pattern?
bill705 posted 10-30-2010 03:07 PM ET (US)     Profile for bill705  Send Email to bill705     

I've got two 10gal tanks from RDS in a 1968 Nauset and the tanks came with WEMA senders installed. They would never read all the way full and they would read empty with about 3gal still in the tank. Don't know if they were right size for tanks or not and there are no adjustments on the senders. Have had the tanks about 6 years.

Last Feb. I installed the Centroid senders and they have worked great so far. I've got the auto ones and didn't have to adjust anything. They now read all the way full and read empty with about 1/2 inch or less in the tank.
They came sized for my tanks, no cutting required.


meridian posted 10-30-2010 03:16 PM ET (US)     Profile for meridian  Send Email to meridian     
It is a 5 hole SAE standard 2-wire.

The tank is 7" deep. If I can't get a sender to read 1/2 full on the gauge = 40 Gal (80 gal total), I'll just calculate how much fuel is contained in the area when the level is at 3 1/2".

vin1722or posted 11-21-2010 02:31 PM ET (US)     Profile for vin1722or  Send Email to vin1722or     
I have a five hole pattern on my fuel tank sending unit which is in a 1994 Outrage 17. It is magnetic and electric. I have a Yamaha gauge on the dash and a gauge on top of the sending unit.
meridian posted 05-22-2011 07:24 AM ET (US)     Profile for meridian  Send Email to meridian     
As a follow-up, I purchased the WEMA unit for $45. My old sender was the swing arm type that was electrically OK but did not give very accurate readings. The new one is very stable and close to actual.
jimh posted 05-22-2011 09:55 AM ET (US)     Profile for jimh  Send Email to jimh     
Many thanks for the first-hand feedback on the WEMA sensor. This is good information to have and adds greatly to the information content of the website.

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.