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Old 24-12-2020, 18:06   #1
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Perkins 4.236 Fuel Consumption

Feliz Nochebuena, companeros!

Recently did a solo overnight motor bc no wind, with hourly fuel checks.
Was using the day tank (34 Gal) and have a full length sight glass tube.
It was full, and calibrated from a jerry can fillup with gas pump diesel.

Kinda shook to see that I was going through 2.5 Gallons per hour.
Madness. Even on a 50' cutter, it should be half that. This engine is maintained.
New lift pump, fresh boil on accessories, clean hoses...

What's the hive mind on what I should be looking at? Dirty Injectors?
Does the Injection Pump need Geritol? Something else?

I apologize if this is taking you away from celebrations tonight,
but my brain won't leave it alone.
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Old 24-12-2020, 18:28   #2
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Re: Perkins 4.236 Fuel Consumption

dirty bottom, prop?
RPM?
Current?
You say calibrated, how finely?
2.5 gpm is about 45hp, well within engine power range.
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Old 24-12-2020, 19:01   #3
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Re: Perkins 4.236 Fuel Consumption

Quote:
Originally Posted by LobeliaBlue View Post
Feliz Nochebuena, companeros!

Recently did a solo overnight motor bc no wind, with hourly fuel checks.
Was using the day tank (34 Gal) and have a full length sight glass tube.
It was full, and calibrated from a jerry can fillup with gas pump diesel.

Kinda shook to see that I was going through 2.5 Gallons per hour.
Madness. Even on a 50' cutter, it should be half that. This engine is maintained.
New lift pump, fresh boil on accessories, clean hoses...

What's the hive mind on what I should be looking at? Dirty Injectors?
Does the Injection Pump need Geritol? Something else?

I apologize if this is taking you away from celebrations tonight,
but my brain won't leave it alone.

What rpm were you running? That seems a bit excessive and agree it should be half of that amount.
Dirty prop?
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Old 24-12-2020, 19:15   #4
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Re: Perkins 4.236 Fuel Consumption

Sorta Dirty bottom and prop, but not heinous.
In the sweet spot about 2400rpm (inop tach)

Following swell on the quarter, slack wind as said.

I'm mystified, memsahib.
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Old 24-12-2020, 19:18   #5
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Re: Perkins 4.236 Fuel Consumption

Calibration: Day tank was empty during filter change, so I filled it with a 5 gal jug,
and put marks on the tank face for each 5G added, next to the sight gauge.
It's better than most swing arm senders...
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Old 24-12-2020, 23:32   #6
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Re: Perkins 4.236 Fuel Consumption

Quote:
Originally Posted by LobeliaBlue View Post
Calibration: Day tank was empty during filter change, so I filled it with a 5 gal jug,
and put marks on the tank face for each 5G added, next to the sight gauge.
It's better than most swing arm senders...


Actually that consumption isnít too bad. Here are the full load figures for a range of Perkins engines and the recommended max continuous cruise rpmClick image for larger version

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Old 25-12-2020, 09:12   #7
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Re: Perkins 4.236 Fuel Consumption

2400 RPM, thats near WOT, Iíd say normal consumption.
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Old 25-12-2020, 09:16   #8
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Re: Perkins 4.236 Fuel Consumption

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Originally Posted by skipperpete View Post
Actually that consumption isnít too bad. Here are the full load figures for a range of Perkins engines and the recommended max continuous cruise rpmAttachment 229316Attachment 229317
Your document was unreadable on my iPad.
I have a 4.236 in my 1983 model Nauticat motorsailer. My maximum rpm is only about 2100 RPM which pushes the boat at about eight knots with a tremendous fuel burn. In flat water with no wind or current I get about 1 gallon per hour at about 1100 RPM which pushes the boat at about five knots. Normal conditions with wind/current/waves is about 1.5 gallon per hour.

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Old 25-12-2020, 09:37   #9
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Re: Perkins 4.236 Fuel Consumption

My understanding from reading the 4.236 manual is 2250 rpm is wot for continuous use and 2500 rpm is "burst" type power.
While I never run ours that high, the table does suggest that what you saw at 2.5 gal/hr isn't to far off expected values.
Also would wonder how well your tach is calibrated/if your tach reading is correct.
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Old 25-12-2020, 09:41   #10
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Re: Perkins 4.236 Fuel Consumption

With the new alternator in, the lead to the Tach is not connected yet.
I'm making a complete guess on RPM
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Old 25-12-2020, 09:42   #11
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Re: Perkins 4.236 Fuel Consumption

What speed were you going at and what is your waterline length and type of hull (displacement, semi-displacement or planing).
You must start from the hull basics because the engine knows nothing about the hull. It just knows that it has to turn a shaft.
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Old 25-12-2020, 09:49   #12
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Re: Perkins 4.236 Fuel Consumption

I have twin 4.236 Perkins on my motorsailer . My governed rpm is 2250. I usually cruise on one engine at 1400 rpm getting 6.5 knots. The boat weighs 21 tons according to the travel lift scales. In my opinion your rpm is too high and you may be under proped. My fuel consumption is 6 liters per hour.
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Old 25-12-2020, 09:49   #13
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Re: Perkins 4.236 Fuel Consumption

I have a First 42 with a Perkins 4-108M. I use about one half gallon per hour plus or minus. A little more during heavy motoring, a little less when battery charging. I do have a racing bottom (all thru hulls flush, wet sanded to 400 to 600 grit) and a feathering prop. But also a custom keel (draws 8 1/2 feet), so a little more wetted surface area. I've never come close to the usage documented in this thread. Lots of things to look at: bottom condition, prop size, fuel injectors (dirty?), injection pump, etc.
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Old 25-12-2020, 10:57   #14
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Re: Perkins 4.236 Fuel Consumption

Weight of boat , engine age, all play a part , but a 4236 is around 2200 revs and can be around 5 to 6 litres per hour , a big thirsty old engine ,but one o f the best
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Old 25-12-2020, 11:13   #15
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Re: Perkins 4.236 Fuel Consumption

My 4.236 powers a C&C landfall 48 at about 6 to 6.5 kts, 1500 rpm with a 23"x23" 3 bladed max prop - uses 5 to 6 litres per hour. Sounds pretty similar to others. Boat is about 43,000 lbs.
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