1998 4.3L Mercruiser Fuel Consumption/Economy

[krakatoa]

Hello Guys!
Long time without post but on back stage reading..

Just looking for info regarding fuel consumption/economy about 4.3L Mercruiser and find some kind of info at different forums but not sure if accurate. Also find this website regardind this matter. Would like to know If this info is correct or If any one by experience now about it.

Just in case my boat is a 2001 Sea Ray 18.5 with a 4.3L Merc

http://www.boat-fuel-economy.com/mer...ion-us-gallons

Thanks for your replies and Merry Xmas to all!

 

[Scott Danforth]

your going to use about 0.4# of fuel per HP per hour with a spark ignited gas motor. so your fuel economy will be dependent on wind, load, seas, trim, hull, and of course, your right hand on the throttle.

too many factors affect hp.

Boating and fuel economy are mutually exclusive unless you have sails or oars.

you can also look up your combination on http://www.boattest.com/ to see a real world test with that hull, motor, and a specific prop with a specific load on a specific day with specific weather.

 

[SeaDooSam]

I got a 96 4.3 and get approximately (from calculations) 8/9 GPH at cruise speed. 18 ish at wot. Do these number sound right to anyone else?
I think the numbers in that website are in the right ballpark but not exact due to many factors affecting fuel economy.

 

[airshot]

SeaDooSam...sounds about right from others I have heard from.

 

[SeaDooSam]

SeaDooSam...sounds about right from others I have heard from.

Great. I was sort wondering myself if those numbers were right

 

[achris]

Had a similar question on a thread over in the Mercruiser forum. I have done a graph of my consumption when I first put my new engine in. HERE is a link to that post.... My boat and your Sea-Ray are quite different, but it does give you an idea of what to expect.

Chris......

 

[krakatoa]

Actually there is like vote option, If click the link there is over 92 % accurate for others. So its close enought then. Want to mention my carb is Mercarb 2 Barrel, its not a TKS (Turn Key System). Dont hink that make any difference since the TKS carb model just removed the choke system and the I/0 engine still 190HP

 

[krakatoa]

I got a 96 4.3 and get approximately (from calculations) 8/9 GPH at cruise speed. 18 ish at wot. Do these number sound right to anyone else?
I think the numbers in that website are in the right ballpark but not exact due to many factors affecting fuel economy.

Dont know your setup but for a 4.3L with alum prop in a 18.5 or 19 ft boat sound too much gas for me.

 

[SeaDooSam]

Dont know your setup but for a 4.3L with alum prop in a 18.5 or 19 ft boat sound too much gas for me.

I went on the higher side because I don't want the OP have higher expectations lol

 

[JoLin]

Everyone's comparing apples to oranges, so I might as well weigh in, too. I use about 8 gph per engine at cruise- 3400 rpm and about 24 mph. I have 4V carbs on vortec 4.3's and my boat weighs 10,000 lbs with a normal load.

What's your cruise rpm? What's your cruise speed? How much time do you spend at no-wake speed? How much time with the hammer down? How rough is the water? How strong is the wind? In short, it's a question that's nearly impossible for anyone else to answer. Here's something I put together and posted on another forum to illustrate just how much consumption can vary. Look at the GPH figures- in my case they're practically meaningless because I'm continually working the throttles.

[FONT=Verdana, Arial, Helvetica][FONT=Verdana, Arial, Helvetica]this past summer I made a week-long, 244 mile round trip through the Great South Bay, Peconic Bay and Long Island Sound, stayed over at 4 different marinas along the way, and made 4 refueling stops. Variable wind and wave conditions. Speeds varying from extensive no-wake zones, to full planing speed, to slogging along at 12 mph getting the crap pounded out of us, to everything in between. Here are the results I logged at my refueling stops. I filled the tank each time and used the logging features of my GPS to record distance and Avg SOG. Distance is recorded in statute miles

Refueling 1 - 69.8 miles , Avg SOG 12.1 , 65.4 gals , 5.75 hours , 11.4 GPH , 1.07 MPG
Refueling 2 - 61.7 miles , Avg SOG 12.2 , 59.7 gals , 6.25 hours , 9.9 GPH , 1.03 MPG
Refueling 3 - 51.0 miles , AVG SOG 19.6 , 49.1 gals , 3.25 hours , 15.1 GPH , 1.04 MPG
Refueling 4 - 62.0 miles , AVG SOG 15.6 , 57.1 gals , 5.50 hours , 10.4 GPH , 1.09 MPG[/FONT][/FONT]

My .02

 

[achris]

JoLin,

I agree with everything you said. One thing will remain a constant though. For the same engine, and the same engine speed, given that the engine is propped correctly, the fuel used per hour will be fairly constant. Obviously the bigger the boat the less miles will be covered at the same engine speed as a smaller boat, but that can easily be factored in to the final figures. The important one is 'gallons (litres for the developed world ) per hour'. Which is why fuel flow meters display in that fashion....

Chris........

 

[krakatoa]

Ok then!
nice info coming thru with the factor of wind, load, seas, trim, hull, and hammer on the throttle as Scott and Jolin said. Also as Chris said bigger boat weight and more fuel burned. But the real scenario for me is the following;

Boating in Tampa Bay and or ICW St Pete
Calm waters
Boat weight2,800 pounds
14x23 alum prop
26 gal tank
and lets said 4 people aboard
Cruise speed no more than 25 to 35

After all info and graphics posted in this thread I could sais the Merc Consumer Chart is close enought to the consumption regarding my boat specs.

 

[krakatoa]

Everyone's comparing apples to oranges, so I might as well weigh in, too. I use about 8 gph per engine at cruise- 3400 rpm and about 24 mph. I have 4V carbs on vortec 4.3's and my boat weighs 10,000 lbs with a normal load.

What's your cruise rpm? What's your cruise speed? How much time do you spend at no-wake speed? How much time with the hammer down? How rough is the water? How strong is the wind? In short, it's a question that's nearly impossible for anyone else to answer. Here's something I put together and posted on another forum to illustrate just how much consumption can vary. Look at the GPH figures- in my case they're practically meaningless because I'm continually working the throttles.

[FONT=Verdana, Arial, Helvetica][FONT=Verdana, Arial, Helvetica]this past summer I made a week-long, 244 mile round trip through the Great South Bay, Peconic Bay and Long Island Sound, stayed over at 4 different marinas along the way, and made 4 refueling stops. Variable wind and wave conditions. Speeds varying from extensive no-wake zones, to full planing speed, to slogging along at 12 mph getting the crap pounded out of us, to everything in between. Here are the results I logged at my refueling stops. I filled the tank each time and used the logging features of my GPS to record distance and Avg SOG. Distance is recorded in statute miles

Refueling 1 - 69.8 miles , Avg SOG 12.1 , 65.4 gals , 5.75 hours , 11.4 GPH , 1.07 MPG
Refueling 2 - 61.7 miles , Avg SOG 12.2 , 59.7 gals , 6.25 hours , 9.9 GPH , 1.03 MPG
Refueling 3 - 51.0 miles , AVG SOG 19.6 , 49.1 gals , 3.25 hours , 15.1 GPH , 1.04 MPG
Refueling 4 - 62.0 miles , AVG SOG 15.6 , 57.1 gals , 5.50 hours , 10.4 GPH , 1.09 MPG[/FONT][/FONT]

My .02

I would like to see a picture of your engine with those carbs. Whatr are the specs of your boat?

 

[JoLin]

For the same engine, and the same engine speed, given that the engine is propped correctly, the fuel used per hour will be fairly constant.

If you have a flo-scan, it's easy enough to see how much fuel you're using at any given point in time, but unless you stay at that rpm, what does it gain you? I agree, it'd be valuable for zeroing in on your most efficient rpm. I have a pretty good idea of what my GPH consumption is at 'best cruise' (somewhere around 8 gph per engine @ 3400-3500 rpm). On a typical run, however, that's maybe 25% of my running time. The rest is spent in no-wake zones or rough water, which has me constantly manipulating the throttles to try and stay on plane without pounding. I'm not arguing against using GPH, mind you, just saying that it in my case it has little practical value.

My .02

 

[JoLin]

I would like to see a picture of your engine with those carbs. Whatr are the specs of your boat?

The carbs are the Merc Weber/Carter 4-barrels. It's a 26'er. LOA with swim platform and bow pulpit is 30'. Beam 9' 6", dry weight 8500, transom deadrise 15 degrees, Merc 'Vengeance' SS props with 19 pitch. I have hit a high of 39 mph at 4800 rpm in calm water. The bridge enclosure canvas was off on that run, and the bimini was folded.

 

[HT32BSX115]

Everyone's comparing apples to oranges,

I think I might disagree with the above and agree with the below!!

your going to use about 0.4# of fuel per HP per hour with a spark ignited gas motor. so your fuel economy will be dependent on wind, load, seas, trim, hull, and of course, your right hand on the throttle.

At 3000 rpm, my 7.4L + Bravo III indicates 10gph when running my nearly 5000lb 21ft 87 Four Winns Liberator at 30 MPH
which yields approx 3 mpg!!

Cheers,

Rick

 

[QBhoy]

If it helps you any...
I have a 5.0mpi which according to the mercury fuel calculator is roughly on a par with the 4.3 tks, if anything slightly thirstier...here is what I have found;
On my 18ft open bow and at 2200 rpm and around 22/23 mph cruise speed, she will roughly use a litre of fuel a mile.
I'd imagine you would be similar, but it depends on your best cruise speed and prop set up, I suppose.
I only know this by knowing how much I have put in the tank and by doing the same journey time and time again at different speeds, loads and conditions.
This is contrary to most information I have read about my engine and similar boat set ups. Most suggest around 3000rpm is best cruise speed....I disagree.
I tend to think the best cruise speed is the lowest revs possible with the boat on the plane, well trimmed and happy at it...not in danger of falling off the plane and not too much bow in the water.

 

[achris]

If it helps you any...
I have a 5.0mpi which according to the mercury fuel calculator is roughly on a par with the 4.3 tks, if anything slightly thirstier...here is what I have found;
On my 18ft open bow and at 2200 rpm and around 22/23 mph cruise speed, she will roughly use a litre of fuel a mile.
I'd imagine you would be similar, but it depends on your best cruise speed and prop set up, I suppose.
I only know this by knowing how much I have put in the tank and by doing the same journey time and time again at different speeds, loads and conditions.
This is contrary to most information I have read about my engine and similar boat set ups. Most suggest around 3000rpm is best cruise speed....I disagree.
I tend to think the best cruise speed is the lowest revs possible with the boat on the plane, well trimmed and happy at it...not in danger of falling off the plane and not too much bow in the water.

Not a valid test. Without a flow meter you can't know what your best economical speed is... You're not accounting for 'no wake' zones, etc. Based on your statement

I tend to think the best cruise speed is the lowest revs possible with the boat on the plane, well trimmed and happy at it.

Then the best speed for my boat is about 11 knots. At that speed I'm using about 1.4 litre/nautical mile. Yet my best ecomony speed is actually 27 knots, where I use about 1.13 litres/nautical mile...

Get a fuel flow meter and do it scientifically.

Chris........

 

[QBhoy]

Chris
With the greatest respect for your post and opinion, I'm pretty sure I am being accurate enough, although admitting it's not scientific.
My boat is in Loch Lomond and conditions are usually fairly constant.
Having spent 30 years doing the same journey in many different boats, the results are usually the same with each boat.
For the well trodden journey or voyage I refer to, I usually put 20-22 litres in the boat each time I do this journey, with the fuel gauge at the same level when leaving the marina. After the journey the fuel gauge returns to the same level each time. I know, I know, it's not totally accurate, but the tank holds 100 litres and is fairly easy to assume levels.
My particular engine seems to use the least fuel at either these rpms and speed or around 1200 rpm and plodding along.
I only presume to be so confident because of the frequency I take this particular journey.
It's definitely at it's happiest at between 2200 rpm and 2400 rpm, at a push. And if nothing else, it more refined and comfortable than at 3000 rpm and pushing on for 40mph.

 

[QBhoy]

I'm constantly astounded at the economy of the boat too at these revs. It's a real jeckyll & Hyde machine. Really good at cruising but horrendous when up and at em at 60 odd mph. You can literally see the fuel gauge moving within 10-20 seconds. Living here in the UK, one might understand why she doesn't see the high end of the rpm gauge too often. Haha