Calibrating Fuel tank sender to EVC With accuracy

[BB marine]

After two boating seasons managing my fuel consumption with the Garmin and also recording all fill amounts in my Log book. I have always been disappointed with the Volvo EVC fuel gauge because it was so inaccurate. This winter I have done some additions to my fuel capacities and while doing them I completely drained my fuel tank. When I drained it My Garmin was showing I had 31.5 gallons left. My Volvo EVC was showing I had 57 gallons left. I knew the Volvo was wrong and that the Garmin was right. After 2 years of resetting the Garmin when refueling and entering fuel amount. It was off by 13.5 gallons I pulled 45 gallons out of the tank. Tank was dry! I contacted Andrew and asked if he could send me a tank drawing. He did! From the drawing I was able to calculate the volume of each inch of the tank. The first 3 inches of the tank the volume is less then the top 7 inches. Also from the drawing I was able to locate the manufacturer of the sending unit, WEMA. I spoke with technician at WEMA now called KUS. The technician gave me the part number of the sending unit. I ordered a sending unit ( now my spare sending unit or remote.) With it I was able to find all the resistance readings and mark their locations for calibrating the tank.

This pictures shows the remote sending unit which is attached to the EVC for calibrations. My VOA is attached to the tank sending unit reading the resistance of 106.3 ohms, which is equal to 41.5 gallons and 37 gallons are usable because the fuel tank pick up is 1 inch off the bottom of the tank and the sending unit is 1 inch off the bottom of the tank. My Calculations for first inch of fuel is 4.50 gallons( rounded). Looking at the markings on the remote sender I determined 119.4 ohms would be 32 gallons or 40%.






I confirmed tank volume setting is correct 80 gallons


I now went to multi point calibrations
First setting is 16 gallons of 20% = 144.3 ohms
second setting is 32 gallons 40% = 119.4 ohms
third setting is 48 gallons 60% = 80.4 ohms
forth setting is 64 gallons 80% = 49.4 ohms
fifth setting is 80 gallons 100 % = 33.4 ohms


Set empty tank



Set 10% alarm


I rewired the EVC harness to the fuel tank and checked results. 41.5 gallons 37 gallons usable . To check accuracy at another level I transferred 20 gallons of fuel main tank to my transfer tank. The main tank EVC gauge reading 16 gallons (1 gallon off) and the needle was just under a 1/4.




80 gallon fuel tanks used by Ranger/ Cutwater (25 tug and 26 Cutwater use this tank, the drawing was for an R25 but the tanks model number matched my tank FO8018) with 10" depth will have accurate reading using the ohm settings I recorded and I believe the 100 gallon tanks would be accurate too if they are 10" tanks. I have alligator clips on my remote sender now. It would take me 5 minutes now to calibrate 80 gallon tank.I will still continue to use my Garmin for a fuel gauge also.

 

[Cutwater28GG]

Bravo Brian! Thats a lot of effort!

can you convert back your new calibrated settings to the old unit every 10 gallons? so for the rest of us we can just manually convert perhaps with a chart to the side of the screen?

i.e. when mine says 70 gallons on the Garmin it actually means x gallons remaining? is that even possible?

(this assumes you have filled to full to reset the total)

 

[BB marine]

The sending unit is not really designed for 10 gallon increments and the Volvo EVC is set up with 20% increments 16 gallons on 80 gallons 20 gallons on 100 gallons. The first 1/4 of a tank -Full to 3/4 the accuracy is less but used in conjunction with the Garmin accuracy is maintained. This is similar to your Truck or car it stays on full for longer time then any other setting. Who cares at nearly full tank . As the fuel gets down to half a tank there are more segments with resistance changes and now the gauge becomes more accurate. Using the gauge in conjunction with the Garmin is a check and balance insuring better accuracy. I never had that before. To adjust the Garmin to read similar to the Volvo EVC I changed the Tank volume to 76 gallons instead of 80 gallons. When I calculated tank volume it figured out to have a rounded off number of 83 gallons. Because of the difficulty filling the tank when it is close to full because the vent and fill are located next to each other I am using 80 gallons and subtracting 4 gallons unusable. This procedure was explained to me by a technician that went to Volvo for certification. He told me they had a full section of training on fuel tank calibrations so the EVC reads accurately. Every boat that they deliver the tanks are calibrated to the EVC. They have several different sending units and tank calibrations done for all model boats they sell. Any 80 gallon fuel capacity Tugs or Cuts can use the recorded numbers I provided. I assume the 27 ranger and 28 Cutwater have the same dimension width and hight tank just longer for the 100 gallon. If the hight is the same 10" the sending unit is most likely the same and should be able to calibrate with the same numbers also.

 

[oneeyedjackass]

Super Cool. I've always ignored the Volvo fuel gauge and just used the Garmin. My thought being that the Garmin was using actual fuel used data from the Volvo computer. Seemed weird and I was never sure if that thinking is correct....Would be nice if they were close

I now went to multi point calibrations
First setting is 16 gallons of 20% = 144.3 ohms
second setting is 32 gallons 40% = 119.4 ohms
third setting is 48 gallons 60% = 80.4 ohms
forth setting is 64 gallons 80% = 49.4 ohms
fifth setting is 80 gallons 100 % = 33.4 ohms

Could I just plug these #'s in?

80 gallon fuel tanks used by Ranger/ Cutwater (25 tug and 26 Cutwater use this tank, the drawing was for an R25 but the tanks model number matched my tank FO8018) with 10" depth will have accurate reading using the ohm settings I recorded and I believe the 100 gallon tanks would be accurate too if they are 10" tanks. I have alligator clips on my remote sender now. It would take me 5 minutes now to calibrate 80 gallon tank.I will still continue to use my Garmin for a fuel gauge also.

Are all the ranger 80gal tanks build to the same spec? Maybe you could post up the tank dim. so us R23'rs could compare. Awesome work!!
mark

 

[BB marine]

Super Cool. I've always ignored the Volvo fuel gauge and just used the Garmin. My thought being that the Garmin was using actual fuel used data from the Volvo computer.
I now went to multi point calibrations
First setting is 16 gallons of 20% = 144.3 ohms
second setting is 32 gallons 40% = 119.4 ohms
third setting is 48 gallons 60% = 80.4 ohms
forth setting is 64 gallons 80% = 49.4 ohms
fifth setting is 80 gallons 100 % = 33.4 ohms

Could I just plug these #'s in? Maybe you could post up the tank dim. so us R23'rs could compare.
mark[/quote]

The 80 gallon tank used in R25 and C26 dimensions that are given in the drawing are 10.5" high , 31.5" wide, 69" long

If you have the same tank dimensions and a Wema or KUS 9 inch sending unit yes you can use the numbers posted.

You are correct the Garmin is using Data from the ECV and displays fuel used and fuel left and is very accurate. I just wanted to have the fuel gauge with better accuracy .

 

[NorthernFocus]

Not sure about the other engine suppliers but the Mercruiser panel has a method for calibrating the tank gauge. Of course it has to be emptied to start with.

 

[BB marine]

Not sure about the other engine suppliers but the Mercruiser panel has a method for calibrating the tank gauge. Of course it has to be emptied to start with.

Volvo also has the multi point calibration. The tank must be empty. Procedure fill the tank by 20% increments, this method of accuracy is ok, and better then then Ranger/Cutwater factory's method of full tank calibration. Using the fuel tank fill method can still be off because of the irregular shape of the tank and the location of the resistance changes in the stem of the sending unit. By using the external sending unit marked where resistance changes I found I could fine tune the level readings to be accurate. Most importantly, 1/2 tank and lower when it really matters. My Garmin and Volvo fuel gauge are reading exactly the same at a half a tank. Is this nessecary? Probably not, but I felt with new style sending units and having the Volvo EVC system it should be much better then it was. When I spoke to a Volvo Technician about how inaccurate it was, his comment was" Really !!! If its set up right it is very accurate". The settings I have now seem accurate but if I feel further adjustments are needed with the external sending unit I can make changes with out draining or adding fuel. Battery power off to the engine ,unplug fuel tank sender, attach alligator clips to EVC sending unit harness, Multi point calibration and adjust.

 

[NorthernFocus]

Not sure about the other engine suppliers but the Mercruiser panel has a method for calibrating the tank gauge. Of course it has to be emptied to start with.

...Using the fuel tank fill method can still be off because of the irregular shape of the tank and the location of the resistance changes in the stem of the sending unit. By using the external sending unit marked where resistance changes I found I could fine tune the level readings to be accurate...

I assume you mean more accurate between calibration points when done the other way. The whole point of doing in-situ calibration is to accommodate irregular shape etc. But presumably the system simply assumes a linear curve between cal points so between points it can be off. But at each cal point is has to be accurate. Unfortunately for the tank in the 25 classics(FO7500) the non-linearity in volume vs. depth is from 1/4 tank to empty. A linear function for that portion of the gauge is WAY off.

 

[BB marine]

Unfortunately for the tank in the 25 classics the non-linearity in volume vs. depth is from 1/4 tank to empty. A linear function for that portion of the gauge is WAY off.

This is also true to the fuel tank in the Cutwater. Bottom of the tank to 1" level is 4 gallons I'm using 4.5 gallons as unusable to be safe. The sending unit doesn't see any of that because it is 9" long and empty is set there. The fuel pick up is also 9" long. So right from the start Full tank or basic multi point calibrations are off because even though it is an 80 gallon tank the most that the sending unit can register is 76 gallons. Then take the "non-linearity in volume vs. depth in 1/4 tank to empty." And it is" way off " 1" to 2"= 6 gallons, and 2" to 3"= 8 gallons 3" to top of the tank each inch is 9 gallons. The first 1/4 section of the sender has 4 different resistance readings that can be used to make that 1/4 tank more accurate. Actually the sender manufacture designed the sending unit to be calibrated with more accuracy at 1/2 tank to empty then half to full. There are 8 resistance changes from empty to 1/2 tank and 3 different resistance changes from half to full. Most tanks irregularity is the bottom half of the tank. For the average boater this is not really that important. I have spent half of my working career dealing with specifications and fits to .0005 so having a fuel gauge thats off 20% or more bothered me. Now that I have messed around with it I thought I would pass it on. I'm happy with the results, I have a fuel gauge that works.