On Sat, 24 Nov 2007 23:49:00 -0500, Wayne.B
wrote:


On Sat, 24 Nov 2007 22:12:41 -0600, Brian Whatcott
wrote:


Diesels don't have this problem, and so are less wasteful at low
revs.


That's true but they have maintenance issues if run at low speed/low
load for extended periods of time.

Bruce said:
Yes there "seems" to be that but mention of "it is bad to run the
engine at low poser" seems confined to the boating world. I've worked
many construction jobs where diesel engines were started in the
morning and shut down at the end of the day. During smoke breaks or
lunch they just sat there and idled. Cranes are a perfect example,
that spend most of their life at very low power settings.

Generator sets - I've never seen a gen set operating manual that said
"run this engine at high power settings".

Not that I'm advocating idling your diesel for days and days but I do
wonder about the people who worry about letting the engine idle. I've
seen people that would hardly let the poor old thing cool down before
stop-cocking it, "because it is bad to let the engine run at low
load".

The Perkins I have in the sail boat has a continuous rating of 3,000
RPM and for years I ran it at 1500 - 1800. When I overhauled it I
could see no evidence of abnormal wear or carbon or any other evidence
that slow running harmed anything.

have the feeling that someone once said "it's not a good idea to
idle a diesel for a long time" and as the message passed from dockie
to dockie it became an urban legend and now everyone is worried about
idling the engine.

But what do I know?

Bruce-in-Bangkok

Bruce, I suspect that all this came about as there are different types
of diesels out there, and *some of them* surely cannot be safely idled
for long periods. I knew a few tow truck operators that drove ford
diesels that told me that if the engines were not equipped with
high-idle switches the engines consistently did not last that long (tow
trucks spend a lot of time at idle). On the other hand, guys that drove
some other brands of tow trucks said they didn't need the fast idle, the
engines lasted just fine. My Dodge/Cummins pickup truck owner's manual
says to avoid idle any longer than 3-5 minutes - kind of a bitch since I
spend half the day in traffic.
In boats we have some (mostly older now) slow-turning diesels that
can be run all year at low speeds without any harm. But I suspect that
most of the newer, lighter, fast turning diesels of recent vintage are
better off above idle.
One more thing... *most* people I've observed around here driving
their boats into the dockage area are idling anyway. By the time they
are docked the engine is already sufficiently cooled and needs no more
idling at the dock, yet they usually spend another five or ten minutes
wasting fuel.
Red