Tomcat fuel capacity vs. gauge readings

M

matt_unique

New member
Well I added my first fuel to the Tomcat yesterday. Just over 32 gallons for $111 - party!

My port tank read E and my starboard tank read 1/4. I added 20 gallons to my port tank and the gauge moved to 1/2. I added 10 gallons to my starboard tank and it went from 1/4 - 1/2. It would appear my gauges reflect only 40 gallons in each tank. Do others have the same experience?

I noticed the fuel gauge goes far below E when the power is shut off. Perhaps it goes quite a bit past F as well to account for the full 75 gallons each tank is supposed to hold?

Thanks for the help.
 
Hi Cap,
Well, ours is a CD25, but we had a similar problem. 100 gal tank, only took 63 gal brand new from the dealer, full to overflow, and full on the gauge. Ran it to show empty, filled it again, 63 gal. We could never figure it out until the dealer gave me a new sender, an aftermarket "universal" one. I installed it per the directions, it cured the problem. Ran it to empty on the gauge the 3rd time & put in 87 gal.
I measured the tank, it's 100gal. It was within a cupla inches of the top when full, only thing we could figure was that there was fuel in it when it came from the factory (very hard to believe), and the gauge read empty.
Who knows, strange things happen. Things don't fail in tandem, but maybe you got 2 bad senders.
 
I have a feeling it's just a sending unit with a limited range of motion. With the power off, the gauge moves a significant distance past E.

Thanks for the reply.
 
I suspect the sending unit is not long enough for the depth of the tank. For instance if you have a fifty gallon tank that is ten inches deep and a sending unit that is only eight inches long, the gauge will read empty with only seven inches (35 gallons) of fuel consumed. You will still have three inches of fuel left (15 gallons) but since the sending unit is completely extended down it will show the tank to be empty. Run the boat until it starts starving for fuel and keep track of when the gauge said empty and how much fuel you have burned since it said empty and you can figure how far off the bottom the sending unit is.
Forrest
 
Just be glad you actually have a fuel gauge. I don't! I use my Yamaha gauges to show me how much fuel I have used and subtract that from 150.

Warren
 
IMHO the marine fuel senders and gauges are not very accurate.

The senders have to be adjusted for various tank depths and the sender/gauge combination is not linear.

I started with empty tanks and filled to the 1/4 mark on the gauge, noted the gas pump reading, filled to 1/2, noted the pump reading and so on till full. My 25 gal tanks on my CD 22 actually held about 9.5 gallons at the 1/4 mark! The newer translucent tanks on the 22's can be read by looking at the fuel level. A much better idea.

Too bad that won't work on the 25's and 255's.
 
I agree - I prefer to be able to put a stick into my tanks and forget fuel gauges all together. Of course on our boats this is impossible.

Ha ha - maybe I'll bring 10G aboard and run her dry sometime to learn how to read the gauge.

Thanks for the replies.
 
We have found the in-dash fuel gauge on Daydream is totally worthless - the Navman fuel computer fuel used/fuel remaining readings on the other hand while not perfect are quite accurate. A very worthwhile addition.
 
There is considerable difference in our gauge reading when cruising and when drifting or at the dock. We will read 1/4 at cruise and flat empty at the dock. The cruise reading is the more accurate. While making two trips to Alaska this past two summers, we have had lots of opportunities to check fuel consumption. I find our gauges are quite accurate when predicting how much fuel will be needed to top off, and how much remaining at a given gauge reading. This information is good only for this boat. Each boat will differ for reasons noted in this thread.
I would suggest making note of gauge level before fueling, guess how much it will take to top off (each side), after a few trips to the fuel dock you should have a good idea of FUEL REMAINING, at a given reading on each tank. I like to give a 10% reserve and when estimating fuel needed for a given leg I use 1.7 mile per gal. for our two 150 hp. Honda engines @ a cruise speed of 22 to 25 mph. Tide in Alaska can have a effect on the numbers but can easily be calculated.
Take time to know your boat, keeping a good log will give a reference to come back to if you feel thing are changing.
 
According to FAA regs, the only time a fuel guage in an aircraft has to be accurate is when it reads empty! :shock: I don't know if there's a corresponding rule for boats. Our fuel gauge was off from day one - never showed full, even when we had fuel running out the vents. Within a few months, it completely quit. We spent last winter cruising in the Keys without a fuel guage; we based our estimated fuel burn on engine hours, and it came out pretty close to actual (and, we never ran out, but always had a 5 gallon spare available, just in case).

We had a fuel flow meter installed, and it is very accurate. At the same time, that Honda dealer replaced our fuel gauge (under warranty), and it has been working fine since. So, we went from one unreliable/non-functional unit, to two working units. I also use the fuel flow meter to trim or adjust throttle for best fuel burn - and that has been the absolute best usage of that instrument.

Yesterday, we cruised around at 1800 RPMs, burning just under one gallon per hour. 2000 RPMs increase that fuel burn to 1.5 gallons per hour with a negligible increase in speed. Same holds true when running in the mid-teens (after getting up on plane) - we get better mpg at 15-17 knots than 12.5-13 (on plane, eased back).

For now, you can get a fuel burn estimate from the manufacturer's site (or one of the boat test sites), and go from there.

Of course, YMMV! :mrgreen: (sorry)

Best wishes,
Jim B.
 
Go buy the Lowrance fuel guages...Only about $150 for the two engines, and you will have peace of mind. The float senders are not accurate, as most above have noted. (Navman/Northstar are very similar)--but Lowarance have many more functions, with the Suzuki engines.
 
Morning..........

I am a bit confused about the fuel consumption on our TomCat equipped with two 2008 Honda 135's.,
as we do not have a fuel flow meter.

(we have been on the Honda web site and there is a fuel management digital gauge that can be installed)

I have read several C-Brats pages on all of these subjects.

With a little chop on the water and both engines running at 4000rpm, I had Lady KC going about 22mph per our Garmin-450 GPS,
but I sure didn't know how much fuel I was using as the gauges provided by C-Dory were very questionable when underway.


If I remember correctly, I believe the previous owner told us that he used about 5 gal per hour running at 23mph.
This means I should be able to travel 250+ miles on 60 gals. per engine.

Per some of the C-Brat input I am not sure how to interpet and calculate how many miles I can travel on 120 gallons of gas at 4000 rpm (60 gal. per engine).


[color=red[i]Question------[/i][/color]

***Can any TomCat owner provide me with some input on this subject of "gallons used per hour"?

x
 
Billy,

Unfortunately, he was quoting fuel use per engine :cry:

At 23 mph, you'll probably use 10-11 gph. At 21 kts, if lightly loaded, we use 11 gph with Honda 150s.

The fuel gauges are pretty accurate with the Honda digital gauges. We usually work off the top half of the tank and fill up. The mpg feature is way off because the gauge uses the pitot pressure for a speed indicator. The gph figure seems right on.
 
I think that the boats with Suzuki 150's run a little faster (and do run lower RPM at the lower cruising speeds--I am about 3200 at 22 mph. I get close to what Roger gets at that speed--about 10 gallons an hour, both the external flow guages and with fill up to fill up.

Figure 2 miles per gallon for both engines (you should do a little better than that, but that gives you a safety margin.)

The 255's hold 150 gallons (a little less is usable)--but a range of 250 is very do-able in almost any conditions and 300 miles in ideal conditions. Your Honda 135's--which will burn the same amount of fuel as Roger's 150s at that speed.
 
We have the Honda gauges with the eight bars instead of E/F. The first time we let it get low on gas the starboard side ran out three miles from the fuel dock. I made it in on the port motor, but was ready to call BoatUS. We have learned that there is at least six gallons of unusable gas in each tank.
 
***
I have looked at these SSI Technology Ultra Sonic Sensors.

QUESTION............

Before I head back to Lady KC,
I was wondering if anyone call tell me
where to find each of the two existing in the fuel tank sensors
and is it easy to remove their covers screws/bolts,
and then physically be able to remove the sensor assembly completely out of both the port and starboard fuel tanks.

What tools would be required to remove these fuel tank sensors.

Does anyone know if the existing in tank sensors are the 33-240 ohm type of resistive float arm.


Begining to wonder about the return on investment........lol

***
 
Can't answer the other stuff but in or around the cockpit step (at the forward end of the cockpit (port and stbd) you should find one or more round access ports, they screw out. Get a flashlight, screw them out and you should see the fuel hose connections and the level sensor attachments. My gauges are extremely inaccurate, I don't use them. Different model years have different access holes/locations.

DSCN2148.sized.jpg

Charlie
 
The top of the tank connections on our TomCat are at the rear of the tanks nearest the stern. Access to this area is through the screwed in side storage areas. Once removed, the rear of the fuel tank is visible.
That is why the gauge reads empty at rest and 1/4 underway.
 
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