Slow cruise problems?

BTDT,

Congratulations! Welcome to the not-so-popular "I've Read My Honda Owners
Manual Club".

Tho no matter to me, your engine(s) will appreciate it.

Curiously, the Honda BF100, a newer model than my 2014 BF90, has the exact
warning about not running below 3,000 RPM more than 30% of the time. Go
figure.

Aye.
 
Bulletin: Worse than running your larger engine(s) at low RPMs most of the
time is not running it (them) at all or very infrequently w/o special care.

Aye.
Grandpa used to say, "If you don't use it, you'll lose it."
 
well, Foggy, you've certainly opened a can of worms. In trying to see exactly what Honda means I downloaded the manual for the Honda 2014 Honda BF90 and went to page 50 as you indicated. Yes, I've got some time to kill.

That page is on how to install the tiller, so I scrolled down. The next few pages describe a fairly rigorous break-in procedure which has limits on running the engine at various RPM's. Later on they mention warming up the motror before using. That's all.

Do you mean the break-in procedure? Otherwise I can't find it where you mentioned. I also looked at the BF100 (the 100 HP version) manual and can't find it.

And yes diesels ignite by compressing the air, but there's not much air in there at idle.

Boris
 
Hi there, Boris.

Thank you for pointing out my error and actually reading/checking my post.
You are now a full phleged member of "I Actually Read and Check Foggys Posts
Club".

My error: For my now sold 2014 Honda BF90s, the Manual page reference
should have been Pg 80 (not Pg 50 - it's another manual referencing another blog
I'm in about how to pith a frog).

For the newer (and improved?) Honda BF100, the identical reference is on Pg 91.

I PMd you those manuals to save you the trouble of finding them again.

So now we're back to that diesel thing. You are correct that "there's not much air
in there at idle". That's the point of high compression. It compresses the required
air and fuel injected into the cylinder for combustion into a very tiney tiny space.
As those molecules get squeezed together, they create a lot of heat which
ignites the mixture without a spark plug creating the heat that gas engines
require.

Realize the amount of "air in there" is the same per stroke at idle or any other
RPM, just more combustion/power stroke cycles/unit time with higher RPMs.
The reason diesel engines don't rev as high as gas engines is because the diesel
gets more work done (read bang for your buck) per stroke than the gas engine.

Now if you think gas engines run hotter than diesels, which thinking I have been
attempting to correct, by placing your fingers up the exhaust of both and then
concluding "Yup, the gas engine runs hotter than the diesel because of higher
combustion temperature in the cylinders", you would also be incorrect.
The diesel combustion chamber temp is higher but the exhaust is cooler (more
efficient combustion produces lower exhaust temps - diesel school 102) due to
something called an air throttle present in gas engines, not diesels.

This should do it.

Aye?
 
Well, I did find it and it says:

"When you check the oil level with the dipstick, you might notice the engine oil appears milky or the oil level has increased. If you notice either condition, change the engine oil. See the following table for an explanation of these conditions.

Result
Running the engine below 3,000 rpm for more than 30% of the time so the engine does not warm up.
Effect
Water condenses in the engine and mixes with the oil, resulting in a milky appearance. OR Unburned fuel mixes with the oil, increasing the volume of oil. The engine oil deteriorates, becomes less efficient as a lubricant, and causes an engine malfunction."

It's under Oil Check not Operation. It's not happened to me and it's not in my manual, but it's good to know. If I found the oil turning milkey, I'd change the oil and check the thermostats. I do run the engine in both the San Juans and SoCal as well as other place in the western US, so maybe the water isn't that cold.

It doesn't say don't run your engine under 3000 RPM, but it does say to check your oil if you do. Good advise and I thank Foggy for bringing it to our attention.

Boris

Boris
 
As long as the engine is up to operating temp--no problem running at lower RPM. BTDT is correct that the modern gas 4 strokes which get 8,000 to 10,000 plus hours are in commercial service where they are run daily--such as CG, Fishing Guides, tow boat operators etc. Often these idle for a long time, but they also have to work hard on occasion.

Diesels are entirely different, and should not be included in this discussion. Some are designed to run at 1800 RPM for years. Others run at 120 RPM max--some new modern high speed like up to 3500, and will have problems if not run up occasionally. One Delta Ferry runs the Diesel 24/7 at 1200 RPM for 2 years (17,520 hours) and then major's it. Never a failure in many years. I have a friend who had an 1800 RPM generator, which had 27,000 hours on it, and never had the lower touched--one valve job at about 14,000 hours. As far as cylinder temp(not sure that is pertinent, but the self-ignition temperature, in the diesel is what ignites the fuel--thus is higher than in the gas engine. If a gas engine has a self-ignition temperature equal to or higher than the fuel, there will be pre-detonation (or "knock") bad for any engine!. Physics Handbook shows ignition temp of #2 diesel to be about 250*C, and gasoline 254* C.

I run a variety of speeds, but as mentioned the Honda are basically car engines, But they are being loaded a lot more than a boat engine at 6 to 8 knots.

I would have no hesitation to run a 150 Honda (or 90) at 2000 Rpm all of the time--as long as I had a temperature gauge and it was up to operating temp--All of the new larger engines allow most of the engine computer information to be shown on the primary MFD, so that is not an issue.

Often factory's put in warnings to be sure that they are covered under warranted issues--If one was really considering running a 150 at 1200 RPM (or any fixed speed) all of the time, it would be prudent to call factory tech and find out what is necessary.

What I find interesting, (I ran thru a number of Honda manuals, trying to find what Foggy mentioned, without success)--is that none said "don't run at full throttle all of the time"--what was mentioned was don't run at full throttle all of the time for the first 8 hours.....so is it OK to run at 5700 all of the time? I would not do that, but it looks like some folks do!
 
that away":1ju7ys8w said:
SNIP
What I find interesting, (I ran thru a number of Honda manuals, trying to find what Foggy mentioned, without success)--is that none said "don't run at full throttle all of the time"--what was mentioned was don't run at full throttle all of the time for the first 8 hours.....so is it OK to run at 5700 all of the time? I would not do that, but it looks like some folks do!
Click to expand...

It's there if you look: 2014 Honda BF90 Manual, Pg 80 and BF100 Manual, Pg 91.

I have not posted to run at full throttle all of the time, which suggestion would be
ridiculous, or any time actually, unless I mentioned it WAY back about my dealer
telling me on delivery his Honda Rep said the biggest problem they were having
then was the piston rings were not seating which could be prevented by WOT
operation "now and then", after break in.

In essence, don't baby your engine. Run it at various RPMs like it was designed
to be operated. Common sense for some but not all.

Aye.
 
And, common courtesy here by most... but not all. If not for that last line, Foggy, it would have been a reasonably helpful post.

Didn't grandma teach you to follow the "just be nice" rule??

Nay.
 
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