Fuel Economy

[jay127]

I've been reading alot of old threads on her and came across one that got me concerned. 3.0 Mercruisers claim to be fuel efficient. I have seen posts ranging from 3-5 mpg. My boat a 1987 19' Wellcarft 192 Classic is averaging maybe 2 mpg at most. I did one trip which was 10 miles and it burned through 10 gallons of gas (rough conditions) Is this do to the size of the boat or should I be having the carb looked at.

Thanks

 

[180shabah]

Re: Fuel Economy

not enough info

Howe fast were you going for that 10 miles?
Was there a considerable amount of idle time - including flush/testing on the trailer?
Any watersports/towing?
Propped correctly?
What load was in the boat?

Now, even without answering any of these questions - 1mpg is WAY low for any 19' runabout.
When was the last tune up? is the choke opening completely? Are you certain about BOTH the distance and fuel burn? Is the sight tube to the fuel pump empty?

 

[jay127]

Re: Fuel Economy

the 10 miles isnt exact but if anything it was less. It has a full tune up. It was out of time a little on that run and ive since timed it. It is doggy on take off but runs great at top end. I dont know what your talking about with a site glass cause ive never seen it on this boat. Thanks for the input. Oh and it was just me in the boat 190lbs and a 12 gallon gas tank (full). Untill i reached my destination . Speed is unknown but around 3000 rpms

 

[superbenk]

Re: Fuel Economy

If it's having a hard time accelerating, maybe it's running rich and dumping too much fuel? I just did a 15-17 mile trip with mixed cruising @ 4000-4500 RPM and puttering @ 2000-3000 RPM. Somewhat choppy out (8-12" chop) and probably burned through 4-5 gallons with my little 4cyl 140hp in a 18' closed bow. Wife & 2 young daughters in the boat with me.

 

[airshot]

Re: Fuel Economy

Definetly sounds like you are using excess fuel, however need to be more accurate in your calculations. Marine engines are calculated in gallons per hour(gph) not mpg, and your 3.0 should be in the 3 to 4 gph at cruising speed (3000/3300 rpm) and can easily jump up to 10 gph when near wot or pulling toys. Heading into a wind or rough seas will also increase fuel consumpsion. Try using a gps for your distance and watch your time running, this will give you a more accurate reading to your fuel usage.

Airshot

 

[floridacruisers]

Re: Fuel Economy

I have a 1989 17' Glastron with the same 3.0L engine. I found out I was burning too much fuel too. Found out the auto choke wasn't opening up all the way and she was running too rich. Try leaning out your choke in steps and see what happens. Worst case would be to set it back to factory specs. Wouldn't hurt to get that carb checked out.
Phil

 

[Mac525]

Re: Fuel Economy

before we really get into any of that what are your wot rpms compared to the manufacturers spec this could very well be a simple prop problem
.... by all means look at the choke for problems. We need some more info to get any where with this one.. Has the proformance of your boat changed over time, how up to date is the maintanance

 

[jay127]

Re: Fuel Economy

The boat is new to me. I bought the hull from my buddy. It had sat for 5 years with a blown motor. I purchased a donor boat with a good 3.0 in it from a engine builder I know. When we took the motor out of the donor boat we put in new fuel filters, cap , rotor, electronic ignition, replaced gas tank,plugs, wires, etc... The prop pitch is unknown to me and the number cant be read do to corrosion on the prop. It does however tach Right at 4400rpms so i think it is propped properly. When I chaged the filter in the bottom of the fuel pump there was alot of gunk built up below it. Could this maybe be in the carb also messing some stuff up?

 

[180shabah]

Re: Fuel Economy

... I dont know what your talking about with a site glass cause ive never seen it on this boat...

Site tube is a clear tube running from the fuel pump to the carb - normally it is empty, but whent he diaphram in the pump ruptures the leakage gets sucked into the carb.

Runs rich - but no explosion.

 

[jay127]

Re: Fuel Economy

Site tube is a clear tube running from the fuel pump to the carb - normally it is empty, but whent he diaphram in the pump ruptures the leakage gets sucked into the carb.

Runs rich - but no explosion.

i will check later today. i take it i want to run the boat and see if any fuel is flowing through?

 

[superbenk]

Re: Fuel Economy

i will check later today. i take it i want to run the boat and see if any fuel is flowing through?

If there's evidence that gas has already been in the tube, you may have a problem. It should be obviously wet inside that tube if fuel has run through it. It should always be bone dry.

 

[45Auto]

Re: Fuel Economy

Marine engines are calculated in gallons per hour(gph) not mpg

Marine engines are not "calculated" in any specific way. GPH (gallons per hour) is just a flow measurement equally applicable to cars, boats, trains, planes, rockets, etc and is useless without speed data. The way the data is used depends on what you're interested in. You allude to this in your next statement where you say:

your 3.0 should be in the 3 to 4 gph at cruising speed (3000/3300 rpm)

If you know GPH and cruising speed then you know MPG, which is what the original poster was asking about .....

A 19' boat is a big boat for a 3.0. He'll probably see around 4 MPG at the best, which would be 6-7 GPH cruising in the mid 20's.