Fuel consuption 97 Marlin

[lapazbajasur]

I have a 97 Marlin with 2 250 two strokes with low hours. I had a fuel feed problem and the mechanic went through everything before finding a clog in the valve atop the main tank. He cleared the clog, and also removed the check spring in the valve atop the tank. He said the check in the bulb at the stern was sufficient for the fuel flow, but a recent trip of about 90 miles- about 60% at 4200 rpms, the rest trolling at about 1000 rpms and some drifting with engines at 600 rpm--used over 100 gallons. This seemed to be very high consumption- what exactly does the spring check in the valve at the tank have to do with fuel flow, could it's removal make consumption higher? Thanks

 

[DennisG01]

The spring/check valve is the anti-siphon valve. If a fuel line would burst, or slip off a nipple somewhere, it's possible for entire tank to siphon itself out into your bilge. It is a CG safety-required device and has no effect on fuel usage since that is entirely controlled by the computer/fuel pump/injectors. Having a larger supply of fuel feeding to the engine doesn't mean it will actually use more. It's only going to use what it wants.

What have you gotten for fuel consumption in the past, when operating under similar conditions?

So you got about an overall average of 1mpg for the trip when running twin engines? Just checking on that. I'll let others comment on what they get or have heard of for similar rigs. However, is it possible your runtime is off? The reason I ask is that 40% of 90 miles is 36 miles of trolling/drifting. At, say, an average speed of 3mph, that's 12 hours of fishing with the engines on. At an average speed of 5mph, that's about 7 hours. Only reason I bring this up is that if your calculations are wrong, that can certainly affect whether or not this average is correct or incorrect (either high or low).

 

[lapazbajasur]

Thanks for the advice- I guess I should have the spring check's reinstalled then. I kept them when the mechanic removed them. The access plate make a it easy to reach.
Also, the timing question concerning the run is valid as my calculations were estimates- except for the distance. We were out about 10 hours, long runs out and in and then about 3+ hours of trolling and drifting so I would guess it was closer to 70%+ plus of higher revolutions for the trip, plus about an hour of checking the motors the day before fishing to be certain the fuel feed problem had been solved, again about 70%+ at higher rpms and slower back in after checking the motors. That time was included in the distance and consumption estimates. The bottom paint had been redone in December along with acid cleaning the trim tabs and painting them so the hull is in good shape, and since the boat is in a marina here in La paz it gets cleaned monthly.

I'm not sure about previous usage as mostly it was calculated at 1.2 to 1.5 mpg as I trolled a lot beginning when I left the marina and I wasn't really careful about those calculations. But, gas here in Mexico just went up 5% per gallon due to a tax increase in Baja effective Jan 1, and the bill for my day on the water really hurt the pocket book.

 

[rsgandy]

I have a 96.. repowered this past summer . I could not repower with anything bigger than the 250s since the hull was not rated for more. I've found the 250 to be very strong relative to the old 2 stroke 250s. The boat rides much higher in the water and cruises more efficiently @ around 4100. We are running a much smaller prop that may have something to do with it. Think the old was a 17.5 and the new is a 15.5. My fuel burn with fly bridge and usually one tank full is between 1.3 and 1.4. getting better as we burn off fuel. We cruise at 30mph. not sure about the WOT but it is less than before.

 

[lapazbajasur]

OK-- thanks-- I've been working on the assumption the main tank is 200 gal and the aux is 54 gal. but I can't find the resource where I got that info. I have the 97 Marlin manual, but I'm having a hard time seeing the gas tank specs in the manual. Am I correct about the gas tank specs?

 

[DennisG01]

If you pop open the deck plate over the tank, you'll have access to the sending unit. Somewhere within visible range of that should be a plate that will give you the tank's specs. Sometimes the plate has printed writing, sometimes engraving. Whether it is still legible after 17 years remains to be seen, though. If you don't see a plate, try another deck plate (if there is one).

 

[Lainie J]

Marlin holds 305 gallons, 2 tanks 150 each, one may hold 155 but 305 is the total. The Sailfish holds 202 gallons, 150 and 52. I have a 1997 Marlin now and had the Sailfish prior.

 

[lapazbajasur]

Thanks-- that make sense as yesterday I ran out on the main after about 150 gal.. Always thought it was 250 and 54 but I'll pull the plate and check to see if I can read it. Don't know where I saw the other specs as it's not in the 97 manual. I always fill up when I come in so never filled it all the way.

 

[Lainie J]

My Marlin is also a 1997.