Diesel Quandary

Rick D · Aug 12, 2009

I'll be interested in other's responses. A turbo is incrementally more finicky. Having said that, they are a standard in commercial applications. At this hour level, I think I would let my evaluation of the overall boat rule. I suspect that evidence of careful maintenance overall would rightly reflect on the engine as well. In either case, they are but 20% gone if they have been maintained and run well. IMHO, of course. Both are good engines and parts should be readily available. Resale is likely a wash.

Ross · Aug 12, 2009

Much will depend on the duty cycle each engine was run at. The older engine may have be run at 75 % for most of its service life and the younger engine may have been run WOT for much of its 3300 hours. You can work even a diesel engine to death if you try hard enough.

RichH · Aug 12, 2009

Probably the old Perkins because it has a lower piston speed and lower rpm per Hp output.
Ross is correct, the best diesel rpm for longevity is 75% of rated max. rpm; but, with the prop at near perfect pitch so the engine isnt 'lugging' (high piston wrist pin pressure). 5,000 hrs. is average life for most non-turbo diesels; but, you can get 10K hrs. if you run at 75% rpm with well matched prop pitch and good basic maintenance. Of course, regularly scheduled oil changes are a must.

Steve Dion · Aug 12, 2009

Yanmars that are "properly" cared for are rated at 10k-12k hrs. I must assume that we need to deduct some percentage for the turbo.

The best engine speed for a Yanmar is about 80% of the max rating.

Ross · Aug 12, 2009

Prime Time said:
The yanmar was installed on a boat before it went on an extended multiyear cruise, so the hours were added during a short period of time.

Long runs I think are better than short runs, I think?
gary

A hundred hours per year involves a lot of non-use. I would go for the younger boat and engine. 3500 hours is not much on a diesel if proper care was given. I have found that about 70% of hull speed gives the best fuel economy. Allowing a world cruise I would think that fuel conservation was important. I doubt that the younger engine has been abused.

Mike Holibar · Aug 12, 2009

The engines are similar cubic capacity and output so starting with both engines new there is probably not much difference. I have heard of M60s doing 8000 hours and Yanmars seem to have similar capabilities also. The difference between the engines is their age. I have an M50 in my boat that is 20 years old, about 3000 hours. Mechanically the engine seems fine although I suspect the bores are glazed due to lots of light running in her past. Apparent problems are with electrics, gaskets and seals which are all tired. I expect that an overhaul will be required in the next two years which aside from seals and gaskets, may involve heat exchanger, exhaust elbow and other parts subject to corrosion, rings and bearings, valve guides and seals etc. Most of the work would be required due to age rather than mechanical wear. In your shoes and assuming all other factors are equal, I would be looking at the Yanmar.
Good luck,

BobM · Aug 13, 2009

In either case

Send a sample of the oil out for analysis. Without that and compression you lack important data.

Stu Jackson · Aug 13, 2009

A two pronged question

1. last longer

2. more trouble-free

Turbo anythings have more moving parts and the turbo components operate at extremely high speeds internally.

Given that, and the shorter run hours, I would personally select the naturall aspirated engine, without a doubt, unless their conditions (either visually or mechanically checked) indicated abuse of the Perkins.

We had Perkins 4-108 (I believe it was) in a rental canal barge in England many years ago. You can imagine the abuse it took in that environment, but it ran and ran and ran...

I also understand that parts are readily available, for both.

Sending out for an oil sample check may not necessarily be helpful as a "one-shot-deal", because the oil sampling usually works by checking different samples over a period of time, like once every four or six months, and comparing them to see differences.

zeehag · Aug 13, 2009

yanmar is an excellent engine..i would trust it after an overhaul to ensure all hours on it were my own
same with perkins
i just bought a perkins 4-108 for my formosa and installed it--is the only one without an engine oil leak at this time--it will have one before a year is out, i am sure-british engines ALL leak oil....but they last forever---just donot connect anything lucas to them or they go dark and quiet lol.....either one is a good choice--remember---there are parts for each--gotta look online....yanmar has parts world wide--as does perkins---but perkins need diapers LOL.....
both last forever unless treated with disrespect..
manuals foreach are also found online---
goood luck and smooth sailing...

Brad Hoff · Aug 13, 2009

You stated that the Yanmar was on a multi-year cruse. What type of battery charging does the boat have? If there is solar, wind charger, etc, these may have kept the batteries mostly charged. Otherwise, the engine may have been run at idle for long periods for charging. Just a thought.