Lifespan of Marine Engines Run at Full Throttle; The Internet as a Source of Misinformation (2024)

I have not had any service issues with the motor. If a motor can be run this hard at WOT and still be a good runner, is there a good reason not to run at full throttle (aside from the fuel efficiency factor)?

Keep up with maintenance and you will be fine. [Introduces new topic: the internet as a source of misinformation--jimh] I am sure several people will tell you the sky is falling and it will ruin your engine but that is what the internet is for. ;)

Mode_Engine RPM__Time
1---Idle---------------40%
2---40% of max------25%
3---60% of max------15%
4---80% of max------14%
5---max speed--------6%

This duty cycle is often used to model the average use of marine engines. As the duty cycle model suggests, most marine engines spend only a very small time at their maximum throttle. To operate an engine at maximum throttle all the time is quite atypical.

ASIDE: One of the great features of the internet is that an individual can make a pronouncement, but such pronouncements are liable to be reviewed by a wide audience, which often finds significant errors in those individual opinions.

I generally do not run very much at WOT because of the fuel consumption. The increase in speed and time savings between WOT and 3/4-throttle is not enough to justify the extra fuel expense in my opinion. If a boat is powered at or near it's maximum horsepower rating, WOT is generally not really necessary for reasonable speed.

The failures of outboards are normally from lack of maintenance, oil, or quality fuel.

To make an inference from the behavior of car engines to boat engines, and to suggest that four-stroke-power-cycle boat engines will tolerate being run at full throttle all the time without any impact on their lifespan seems to me to be quite an inappropriate association.

The more the misinformation confirms your previously held belief, the more likely you are to accept the misinformation as fact.

I would bet they are still run about 40% at idle but I think the higher RPMs will have a higher percentage of time than the Chart shows.

Does the ICOMIA36-88 chart indicate what size engines it used to get the data?

I do agree with it for larger HP engines, because my 90hp Etec much to my surprise shows an RPM history that is very similar to the chart.

From ICOMIA36-88
"During the 1971-1972 boating season, Outboard Marine Corporation (OMC) conducted a usage study on eleven boats powered by their engines. Engine speed was recorded and operators noted specific information about the craft and boating activities. Approximately 200 hours of usage data was obtained. The NMMA began expanding the study in 1973 to include a wider variety of engines and geographic areas. An additional 33 boats produced 160 hours usage data. The data was analyzed and reduced at the University of Wisconsin."

If I am interpreting this correctly, I think the chart was made from a pretty small sample, 44 boats 360 hours. I might have missed something. There are a lot of pages and I was moving pretty fast.

http://wvuscholar.wvu.edu:8881//exlibris/dtl/d3_1/apache_media/ L2V4bGlicmlzL2R0bC9kM18xL2FwYWNoZV9tZWRpYS80NzY4.pdf

The above research paper gives some background on outboard engine duty cycle testing. See folios 5 through 7.

The ICOMIA 36-88 duty cycle standard is also used by the Environmental Protection Agency as the basis for their evaluation of outboard engine exhaust emission. It is also adopted by the International Standards Organization (ISO).

You can read the standard at the ICOMIA library on-line at

http://www.icomia.com/library/Default.aspx?LibraryDocumentId=945

There is often anecdotal evidence from boaters, usually contrary first-hand reports, albeit completely undocumented and given from recollections or impressions rather than from actual data, that typical outboard engine use is substantially different from the duty cycle suggested in the ICOMIA 36-88 standard. For one such typical recitation of contrary claims, see

http://continuouswave.com/ubb/Forum1/HTML/018262.html

The above even alleges that the duty cycle was intentionally (and perhaps nefariously) crafted to contain a bias against two-stroke-power-cycle engines so they would test poorly for exhaust emission when later, the EPA would use the duty cycle as the basis for its emission testing.

My own experience, where the actual duty cycle of my outboard engine has been carefully recorded by a digital data recorder in the engine itself, has tended to show that the ICOMIA 36-88 standard, if anything, tends to overstate the amount of time the engine will be operated at full throttle. Using the data from my engine and its last 300-hours of operation, running at full throttle has occurred for only a very tiny fraction of the time and not anywhere close to the six-percent of the time used in the standard. So on the basis of my actual recorded data from my actual use, it appears to me that the ICOMIA 36-88 duty cycle standard is probably reasonably typical of outboard engine operation for an average. The suggestion that operation at maximum power is a very substantial part of the duty cycle of an outboard engine just does not seem to be supported by anything other than anecdotal testimony which on examination appears to be simply guesswork by operators rather than any sort of accurate record.

I have not seen any sort of real data or survey which would make me want to discard the ICOMIA 36-88 standard and replace it with an alternative. Although it may not meet the demands of a couple of old boaters, it seems to meet the rigor of the ISO and EPA.

quote:The purpose of this standard is to provide a standard duty cycle which corresponds closely enough to average consumer use so that average or composite values of important engine parameters...may be compared in a simple and rational manner.

Source: ICOMIA 36-88

We know that engine wear is related to the number of operating cycles. It is clear that if an engine is operated for a particular time, say 100-hours, it will execute more cycles in that time as its operating speed increases. We also know that wear is proportional to total number of cycles. Therefore an engine operated at a higher speed will experience more wear, and the wear must increase linearly with engine speed.

On a closer examination, we can also see that in a reciprocating movement, like that of a piston, there are forces exerted that are proportional to velocity to the second exponent. The piston speed increases with engine speed, and thus the force applied to create the higher speed varies with the square of the speed. With greater forces comes greater wear. We now see that there is a possibility for the wear on the engine to increase with engine speed in an exponential manner.

On these two simple observations it is possible to dismiss the claim that operation of an engine at its maximum speed will not have any effect of life span or durability. Clearly it will. To claim otherwise is to ignore common sense.

I do not seen anything in that research paper written by someone else that says running at wide open throttle is bad? I didnt not see the part where it says that it will blow up your engine? All that shows is what norm for running is.

The truth is that most outboard can live all the way to 8600+ hours without issue. As a recreational user, you most likely will never rack up enough hours to wear an engine out.

From real world experience which including tearing down engines, I can tell you are not doing any damage by running engine at wide open throttle.

To clear up misattributed quoted material is not particularly something that is causal to or related to the experience one has with operating outboard engines. If you need more help in understanding why, as the moderator, I would like to clear up errors made in attribution of quoted material, and how this desire is not particularly reflective of my boating experience, I would be glad to explain further, but contact me via email.

To suggest that correction of misattributed quoted material reflects some general inability of a person to understand fundamental principles of physics is not a very good argument to make. There seems to be no correlation at all.

The basis for my assessment of an increase in engine wear with increased operating speed is not made by reference to any research paper. This accusation seems to have been made by a misreading of what was said. Let me quote myself to clear this up:

quote:To summarize the general claim, we can describe it as follows: operation at continuous full throttle will not affect engine life span, reliability, or durability. We can analyze this claim on the most simple basis: common sense.

If anyone wants to take the opposing view, please explain how common sense is to be ignored in the case of engine operation.

The offer of anecdotal experience in disassembly of engines is interesting, but I do not see any data. The engines are just said to have been disassembled. There is no data about wear of these engines run at constant full throttle compared to engines run according to the recognized standard for duty cycle.

This seems to me to demonstrate the difference between rational thinking and repeated reinforcement of previously held beliefs.

quote:I can tell you are not doing any damage by running engine at wide open throttle.

I do not believe there is any dispute in this regard. This is not the focus of the discussion. I do not believe anyone is making an argument against this particular claim. Any engine can be run at its rated power, but not forever and not all the time.

What has been claimed, and what seems to be in dispute, is the question of the effect on constant operation at wide-open throttle on engine life span. The claim has been made that there is no effect on engine life span from constant operation at wide-open throttle. This claims is dismissed on the basis of common sense.

We can see an example of the influence on engine lifespan and engine operating speed from engines used in stationary power generation. Such engines are used for extremely long periods of operation at their rated power. It is typical that an engine used in stationary power generation will be significantly derated for that application compared to a similar engine used in marine propulsion. An engine rated at 300-HP for marine propulsion might be derated to 150-HP for use in stationary power generation. This is expected, based on the common sense principles of wear I explained above. On the other hand, if operation at maximum throttle for long periods--constant operation at maximum throttle--is to have no effect, then there would be no derating of engines for stationary power generation.

And those numbers are real, which is why I don't worry even a little about my Cat's.

Dave

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However, I am quite sure that there are many components inside an engine where wear increases more than linearly with speed, friction being the obvious case, where double the rpm probably gets you well more than double the heat

My Outrage 25 is considerably overpowered. Using 21" Revolution-4 props (more like 23's-with very strong mid-range capabilities) I can cruise this big boat for hours at only 2500 RPM and 27 MPH, with the engines quietly loafing along. Not much piston travel there. They now have over 3200 hours on them, and still factory spec compression.

Without catastrophic failures, such as thrown rod or bearing failure, etc, outboards can just plain wear out, necessitating a rebuild or a replacement. Rings wear, cylinder bores wear out of round, losing compression and HP, and reeds can wear out, causing low speed idle problems. That's why piston travel counts. I completely wore out the powerhead of a Mercury I-6 on my Nauset after 14 years of intensive use, never having a failure. It just died of wear and old age. The solution was either to re-build or replace. I replaced, and now still run that engine 29 years later.

Here we focus on the life span of engines which are run at continuously at full throttle.

Dave--you have reminded me of an engine from my past, a Yanmar diesel from an old sailboat. In the Yanmar manual, the engine was rated for continuous operation at about 3,000-RPM. The maximum throttle speed of the engine was about 3,300-RPM. At that engine speed it was rated for one hour of operation. This is another example of the severe de-rating of engine operating that occurs in the real world with real engines. Of course, this confirms my common sense analysis of the problem. This example is based on the ratings of the engine from the manufacturer. This is not based on anecdotal recollections of engine which I disassembled.

quote:I would argue that 99.99 percent of recreational outboard engine users will never "wear their engine out".

How many engines were involved in the study that produced this outcome?

quote:That's why piston travel counts.

Yes, I agree. It is just common sense that the greater movement of a piston over time the more wear will occur.

In addition, piston speed also counts. The faster the piston moves, the greater the forces that are involved. Also the greater the acceleration and deceleration of the piston at the top and bottom of its reciprocal motion in the cylinder. It is just common sense that the faster the travel the greater the forces, and therefore the greater the wear. Wear is proportional to the friction and the force. If you do not understand this, take a piece of sand paper, and rub it against a surface you want to abrade. Now rub it with much greater force. See which action causes more abrasion. This is such a common sense notion that people understand it intuitively. To say that one can run an engine continuously at its maximum speed and power and expect there to be no affect on the life span of the engine is just not common sense. So far I have not read one word that would cause me to change my opinion.

I think common sense will illustrate that time at WOT is a not an issue for a recreational user and they just dont wear out. The average boater does what 35-40hrs per year on their boat? At what point does an outboard wear out?

quote:The average boater does what 35-40hrs per year on their boat?

Thanks for this interesting data on average boat use. It is good to have an accurate figure for this, and this datum will be very useful.

quote:In reality running your engine at WOT will not decrease its usable life.

Thanks again for this information. It is wonderful to know that I can now begin to run my engine at its maximum power output for as long as I wish without having any effect of the anticipated life of the engine. Great news!

Thank you for quoting other peoples ideas and insight jimh instead of having your own thoughts.

--the new topic was a discussion about the discussion; discussions do not discuss themselves;

--the new article was not about our topic here in this thread. The topic here is the life span of marine engines run at full throttle.

Larry--if you insist on posting articles that try to drag the discussion away from the main topic, you can be sure they will be deleted. Please contact me via email in the next day or two to discuss this further--jimh]

quote:I give up.

If you gave up, why did you keep going trying to make your point one last time?