Fuel capacity issue

jmznshana · Jun 18, 2012

Hello.. My first post. been lurking for a while...

I bought a 1996 Montery Montura 196 2 months ago. Awsome boat so far with only some minor issues I will be inquiring about here on thought to fix.

The boat is powered by a 5.7 Merc. with a 20 gal. fuel tank. What I am trying to find out is if ths boat may have originally came with a 4.3L that would have fit that tank size more appropriatly. The guy I bought the boat from replaced the motor 4 years ago and said the original was a V8 also.

I estimate I am getting about 3/4 a mile per gallon. I primarily will be using on the ICWs' of th Cape Canaveral FL. area. I'm not sure if this is normal or not for this engine. It seems to be running smooth with no issues so far. If this is accurate usage does anyone know if it is possible to have a larger capacity fuel tank made and installed in this boat. I do not know what the sub structure is like under the floor on this boat an if that will even allow this type of mod.

Any thoughts? I really would like to get more distance available as it seems I am limited for range right now.

spdracr39 · Jun 18, 2012

Re: Fuel capacity issue

That seems small. All the v8 boats I have seen have at least a 35 gallon tank. Mine has a 45 gallon. 20 gallons would last me about 4 1/2 hours.

QC · Jun 18, 2012

Re: Fuel capacity issue

3 to 4 MPG makes sense to me. 3/4 does not. There are a lot of 20 footers with 20 gallon tanks. Not necessarily tied to engine size, and the MPG would not be that different anyway.

Welcome aboard!!

Edit: I am finding this boat with 5.0s and 5.7s. Confirm the mileage and we'll go from there. 3/4 MPG would mean 15 miles and empty. Tell us how you're operating her too. RPM? Speed?

jmznshana · Jun 18, 2012

Re: Fuel capacity issue

QC said:
3 to 4 MPG makes sense to me. 3/4 does not. There are a lot of 20 footers with 20 gallon tanks. Not necessarily tied to engine size, and the MPG would not be that different anyway.

Welcome aboard!!

Edit: I am finding this boat with 5.0s and 5.7s. Confirm the mileage and we'll go from there. 3/4 MPG would mean 15 miles and empty. Tell us how you're operating her too. RPM? Speed?

I just looked at a chart for the area I traveled last trip. I went roughly 28-30 miles and used 17.5 gallons based on the fillup after the trip. (started full tank)

6 of those miles were at no wake speed and the rest were at around 3400 rpm cruise at 25-30 mph give or take. No hot dogging or pulling anyone. I will track exact next trip.

prop is a SS 23p

QC · Jun 18, 2012

Re: Fuel capacity issue

Direct trip? No tubing, skiing etc. No turning around? That sounds closer to 2 which is still really poor. Not unbelievable, but not good..

jmznshana · Jun 18, 2012

Re: Fuel capacity issue

QC said:
Direct trip? No tubing, skiing etc. No turning around? That sounds closer to 2 which is still really poor. Not unbelievable, but not good..

Correct. Direct trip

Any suggestions on how to squeeze out some better MPG's. Annual tune up was done just prior to purchase. I was provided all maintenance records and reciepts to document.

Prop? I also just installed smart tabs.

QC · Jun 18, 2012

Re: Fuel capacity issue

I reread your post, if your wakeless speed was below say 800 RPM, then I think you have followed what I would recommend. Look at some test data at Boattest.com. You'll find best fuel economy is almost always at wakeless speed, and then usually just onto an efficient plane around 25 MPH, and 3500 RPM. Not sure what else you could do differently at this point. Something is wrong and I am little concerned that it was the refill until you duplicate. Any smoke or smell?

Chris1956 · Jun 19, 2012

Re: Fuel capacity issue

I am surprized the fuel tank is that small. My 18' SeaRay came with a 35G tank and a 4.3LX motor. That served me pretty well, but I got a lot better fuel mileage than you report. I would think a 45G tank is a better fit. Why not check to see if the tank is original and if there is additional space to install a larger tank? Your prop may be a bit tall, causing you to lug the motor and decrease fuel mileage.

Fireman431 · Jun 19, 2012

Re: Fuel capacity issue

Start with a tune-up. Fill the tank and run a set route. Refill and recheck your fuel use. You should be getting at least 2 mpg, depending on weight, loading, wind, currents, etc.

Chris1956 · Jun 19, 2012

Re: Fuel capacity issue

I once took my SR out to the Barnegat Ridge. That is 20 miles out in the Atlantic, and 20 back, plus the 20 miles from my dock to the inlet in a round trip. I used about 24Gal/60+ miles, if I remember correctly. I could have gotten fuel just inside the inlet, if I would have needed it.

jmznshana · Jun 19, 2012

Re: Fuel capacity issue

Chris1956 said:
I am surprized the fuel tank is that small. My 18' SeaRay came with a 35G tank and a 4.3LX motor. That served me pretty well, but I got a lot better fuel mileage than you report. I would think a 45G tank is a better fit. Why not check to see if the tank is original and if there is additional space to install a larger tank? Your prop may be a bit tall, causing you to lug the motor and decrease fuel mileage.

Only problem with easily checking to see if there is additional space to put a larger tank in is the guy has a new floor put in a few years ago and there is no access to see under the deck. The ski locker was also floored over... I was hoping for someone that is familiar with the insides under the floor of this boat or similar would chime in if this was a possible mod.

Can you explain the prop "lug" thought? I am not sure where I really should be for prop pitch.

Philster · Jun 19, 2012

Re: Fuel capacity issue

When you run on plane, are you 'trimmed out'?

Did you get the boat checked or weighed? A mid 1990's bowrider that is watterlogged and carrying around heavy, wet foam would shock no one.

The 23p prop could be lugging the engine if she is heavy from being waterlogged. This would compound the problem.

QC · Jun 19, 2012

Re: Fuel capacity issue

I DO NOT recommend this, but . . . A little lug should actually help with fuel efficiency at moderate cruising speeds. Valves don't like it, but I personally don't think that is the issue here.

Edit: Simul Phil. I was reacting to Chris' post. The combo of overweight and the 23 could indeed be an issue. But I still think there is something wrong with either the numbers or the engine. My thoughts are that a very heavy 23 footer should eek out 3 MPG as the OP describes his trip. A waterlogged 20 with a good cruise speed should as well.

Philster · Jun 19, 2012

Re: Fuel capacity issue

Also adding that when you are off plane, you do not want to be pushing a bow wave. Off plane should be 'idle speed' or what I called 'puttering around'.

But... I'm leaning towards waterlogged boat as the biggest factor, with several other smaller issues as possibilities.

QC · Jun 19, 2012

Re: Fuel capacity issue

Philster said:
Also adding that when you are off plane, you do not want to be pushing a bow wave.

Agree, and why I used "wakeless".

Philster · Jun 19, 2012

Re: Fuel capacity issue

QC said:
Edit: Simul Phil. I was reacting to Chris' post. The combo of overweight and the 23 could indeed be an issue. But I still think there is something wrong with either the numbers or the engine. My thoughts are that a very heavy 23 footer should eek out 3 MPG as the OP describes his trip. A waterlogged 20 with a good cruise speed should as well.

Agreed. It's still low, even if it's heavy.

jmznshana · Jun 19, 2012

Re: Fuel capacity issue

Philster said:
When you run on plane, are you 'trimmed out'?

Did you get the boat checked or weighed? A mid 1990's bowrider that is watterlogged and carrying around heavy, wet foam would shock no one.

The 23p prop could be lugging the engine if she is heavy from being waterlogged. This would compound the problem.

Waterlogged foam.... Hmmm now I am wondering. The seller did tell me at one time he took on water from a seperated (rub trim bumper? It that what the rubber trim is called around the boat exterior?) around the boat. The transom area appeared to be the worse although I do see sealant in a few other places.(he provided a reciept for the repair) There is also a very small dime size piece of gel coat chipped off the hull on the lower side about 3/4 way down from the bow. He said he hit something in the water and it just appeared as a crack in gel coat until a few weeks prior to selling when a piece chipped off.. It does not appear there is a crack in the glass and I band aid patched it with some waterweld as a temporary patch. If there is a crack in the glass that is/was letting water in that location could that water make it's way to the foam?

Where all under the floor is the foam located? How can I check it for water? What is it's purpose?

Also what is motor Lugging?

Thank you all for the time..

jmznshana · Jun 19, 2012

Re: Fuel capacity issue

Also when on plane I run the trim about a quarter way up based on the trim gauge...

Fireman431 · Jun 19, 2012

Re: Fuel capacity issue

jmznshana said:
seperated (rub trim bumper? It that what the rubber trim is called around the boat exterior?)

Rub Rail...

He said he hit something in the water and it just appeared as a crack in gel coat until a few weeks prior to selling when a piece chipped off..

How convenient...juuussstt happened

If there is a crack in the glass that is/was letting water in that location could that water make it's way to the foam?

Yep

Where all under the floor is the foam located?

Most everywhere...clear up to the bow

How can I check it for water?

Open a piece of the floor (preferably a hatch or screw down inspection cover and pull out a sample

What is it's purpose?

FLOATION foam...

Also what is motor Lugging?

Overloading the motor. like trying to drive with the emergency brake partially on. Burning a lot of fuel to compensate for the additional weight of trapped water (8.3 lbs/gallon...100 gallons = 830 lbs)

jmznshana · Jun 19, 2012

Re: Fuel capacity issue

Fireman431 said:
Rub Rail...

How convenient...juuussstt happened

Yep

Most everywhere...clear up to the bow

Open a piece of the floor (preferably a hatch or screw down inspection cover and pull out a sample

FLOATION foam...

Overloading the motor. like trying to drive with the emergency brake partially on. Burning a lot of fuel to compensate for the additional weight of trapped water (8.3 lbs/gallon...100 gallons = 830 lbs)

Thank you... I will have to pull carpet and see what I can find... He had a new floor put in 2 years ago and the ski locker was covered over.

Now I am a little scared.. Being new to boat ownership I did not think about this possibility prior. he was upfront and did tell me the boat took on water at one time. Enough to get the starter in the bilge submerged and toast it. And the reason he replaced the floor was it was rotted. He said it had the typical Monterey ski locker drainage issue. ( it did not drain) I don't know if the guts under the floor were thoroughly dried out or replaced. And not sure if the floor was done before or after the water intrusion issue. I will have to check the receipt dates fore repairs when I get home tomorrow.

Does anyone know if there is an online resource for boat specs for this year and model of boat. I have looked with no luck. I want to go have it weighed now and compare to factory specs.

Fireman 341 where do you work? I am with Tavares FD

Fuel capacity issue

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