Perkins Diesel

[dartagnan]

I'm looking at a 1985 Trawler with Perkins 635444M diesel engines with about 3500 hrs. Does anyone know the fuel economy on these engines? How do they compare to the Ford 120's? Thank you!

 

[High Wire]

Welcome aboard.
On a 36 Monk, about 1.8-2 GPH at 1700 RPM which gives 6.7-6.9 knots speed.
The Perkins is almost identical in fuel consumption the the Lehman.

 

[dartagnan]

Perkins

Thank you! I kinda thought that but wanted to hear from someone who had one.

 

[DaveGibson]

My Perkins 120s were the same as Ford 120s. Anywhere from five to eight gallons per hour each.

 

[Pete Meisinger]

Come on, really?

Two Perkins pushing an 80 foot boat at WOT will give different results than the same engines at about 1500 rpm in a 32 footer.

Fill in the blanks for us.

pete

 

[GaryPete]

I have a pair of these identical engines in my 1987 40’ Defever, 34000# displacement. At 1800 rpm, 8.5kts and 2.5gph total is what I plan. It’s usually spot on. At 2200rpm I can push 9.5kts but the fuel burn is 3.5-4gph. The sweet spot on my Perkins is 1800 and they purr like a kitten. Engine time 2200hrs.

 

[mcarthur]

Generally, diesels have pretty much the same consumption - if you ignore the boat! So one diesel is probably going to be within 10-20% of any other diesel engine. Common rail, contrary to some popular opinion, did very little for fuel consumption but did a lot in other ways (reduction of greenhouse gasses and less weight for example). Even turbos and aftercoolers didn't help consumption, but did get more power out of the same size engine (power is not fuel consumption!). Many points about this are around, this one is but one example.

 

[mvweebles]

Generally, diesels have pretty much the same consumption - if you ignore the boat! So one diesel is probably going to be within 10-20% of any other diesel engine. Common rail, contrary to some popular opinion, did very little for fuel consumption but did a lot in other ways (reduction of greenhouse gasses and less weight for example). Even turbos and aftercoolers didn't help consumption, but did get more power out of the same size engine (power is not fuel consumption!). Many points about this are around, this one is but one example.

I respectfully disagree that all Diesels burn approx same fuel regardless of technology (turbo, after cooler, common rail, electronic controls, etc). Fuel efficiency has improved over the years due to these tech improvements. I chose an old-school natural Perkins 4.236 due to ease of repair within my skill level. But my experience is a JD 4045 TA would be 30%+ more efficient. A GM 4.53 would be at least 10% less efficient.

Peter

 

[Max Simmons]

Twin Perk 135's pushing 38' @ around 7.5-8 knts, average 3 gal/Hour total.

 

[ufish2]

I have a 1983 Perkins 6.354 185 turbo with 3500 hours. At 7.5 knots and 1600 rpms I burn 2.5 gph a little less if going with the current. 38ft boat. very pleased. The majority of the time I ride the current and every once in a while I'll take the engine down to 1200rpm and run the engine at 1800 rpm before shutdown. At 1200rpm I'll burn around 1.75 gph still running 6 knots when in no hurry and calm seas.

 

[mvweebles]

When I was delivering, I didn't even ask owners what their fuel economy was. Always wrong, always optimistic. If I had listened to them, I'd still be floating out of fuel 100 nms off the California coast.

The numbers in this thread vary wildly and makes the point.

 

[slowgoesit]

My Perkins 120s were the same as Ford 120s. Anywhere from five to eight gallons per hour each.

If a Ford Lehman 120 is burning five to eight gallons per hour, either it's being operated at or near WOT, or there is something seriously wrong . . .

 

[C lectric]

If a Ford Lehman 120 is burning five to eight gallons per hour, either it's being operated at or near WOT, or there is something seriously wrong . . .

Agree. Most of these old N.A. units would produce about 16-17HP per gal used per hour. Which is just about what is quoted at 8GPH. The catch is those figures are at WOT under FULL load.

Most of these engines in slow boat/trawler service are NOT operated anywhere near full revs or WOT except for testing and a VERY short time. Most of these engines, to produce just under hull speed, produce somewhere around 30HP - 40 HP which is about 2 -3 GPH or a bit more/less.

THat quoted 5-8 gph is if that engine was run at WOT or close to it. THe 5 GPH would be hard run, the 8GPH is abuse for hour on hour use.

My own quite different engine, although roughly the same age and also N.A., and potentially much more powerfull burns about 9 -10 litres at 1,800 revs or about 2.7 GPH but at full rated rev/full load will burn about 13GPH or 49.2 LPH.

So yes, the figures of between 2.0 and 3.0 GPH are reasonable figures depending upon the boat itself, the owner and how it is run.

And yes, there will be differences between a Lehman and a Perkins when used in the same boat. But the difference will be small.