Does running WOT for an extended time cause enginge damage

[Mark Prouty]

IMHO it does not if Properly Propped.

Any empirical data to the contrary?

[Don T]

Hello:
Well, if everything is set up proper it shouldn't be a problem with either type of motor. That being said, when I changed to the BWY prop for the Tohatsu 50, it topped out at 5500 rpm which is the upper limit (was 5100 rpm). When I run at WFO for a while it doesn't idle afterwards. This isn't something I noticed before. It makes me wonder about reed valve fatigue etc.

[Robert]

I ran my Suzuki DF50 wide open very often and sometimes for 3 hours with no problems or changes in behavior. Running WFO so often is why I want a bigger motor that can go 20 mph at a quieter 2/3 throttle.
..
Don T, did your Tohatsu return to normal idle after it cooled off?

[They Theirs]

New direct injected 2-strokes internal engine bearings and cylinder temperatures are extreme because they no longer have oil enriched fuel flowing through the crankcase. I believe the future of 2 cycle engines have not been proven with the low emission standards. The proven durability of the 4-stroke technology made famous by the Honda with some 40 years rough service.

Sorry Chip, I took leave of saying "New Direct Cylinder Fuel Injection", opposed to old two stroke metered Oil injected into the crankcase fuel.

Smart Synthetics on 2-cycle lubrication Quote:
"Because the fuel no longer passes through the engine to help carry the oil and provide additional cooling, direct fuel injected engines are more highly stressed and operate at higher temperatures. While OEMs have gone to great lengths to ensure that their fuel injected engines can operate on TC-W3 oil, they recommend their genuine oils for optimum performance."

[Chip Hindes]

New direct injected 2-strokes internal engine bearings and cylinder temperatures are extreme because they no longer have oil enriched fuel flowing through the crankcase.

What are you talking about? "New" oil injected two strokes have been around in outboards for twenty years, way longer than most four strokes. Oil injected Yamaha and Kawasaki and ?? motorcyles since the late 60's. The Tohatsu/Nissan outboard twins are legendary for their durability.

Direct fuel injected two strokes are relativley new, but the injected four strokes haven't been around that long either, and don't forget the proven Honda four strokes of which you speak are (still) carbureted.

[Mark Chamberlain]

My honda 50 has burned 12 gallons of gas at 5100 rpm none stop with no damamge.
I often run 3 hours straight at 5500 rpm.

I have changed my impeller every two years just for safety and oil (Mobil 1) every 40 hours as well as the filter. I run Seafoam in the gas at least 2 cans a season.

My engine has 500 hours and I expect to get 1800 hours out of it before considering a power head replace.

the engine hits about 5900 top rpm with a 12x10 prop
5100 rpm nets 14 mph loaded fairly heavy with weeks water and provisions.

WindMusher.com
Now Harbored in Valdez Alaska
PWSSS.com

[Chip Hindes]

What's your definition of damage?

Can the motor be run hours at a time at WOT without self destructing? Yes.

Is is harder on the motor to run it 25 miles at WOT, rather than 25 miles at 2000RPM? Yes.

Deny that and you're fooling yourself.

[Night Sailor]

IF, the owner does the factory recommended maintenance, and uses the factory recommended fuels and lubes, or better, no harm is done to a motor, whether two or four stroke if it is operated within it's designed operating range, which is usually about the top 500 rpm for 2 strokes. Sure it will wear faster, but it is normal wear, not catastrophic damage. This from an enineer who retired from quality control at Ford after 20 yrs,, and then retired from quality control at Bell Helicopter after another 20. The fuel, lube and water criteria are established to be adequate, plus a safety margin, for the top recommended operating range with careful lab testing, then feild use in salt and fresh water. Since 2 strokes get more of their hp at the top end, the factory expects owners to use that end of the rpm range. The safety margin is consdideration for the normal owner that never reads the owner's manual and neglects his maintenace schedule or uses inferior fuels or lubes to try to save a few cents at the risk of the entire engine failing.

As far as outboards go, I've run my '97 Merc 50 classic 2 stroke with oil injection, about two hours at WOT (5400) on many occasions, one hour on most every cruise, but usually cruise at about 4000 (10 mph), for better fuel economy. The Merc has never had any mechanical repairs (electrical relay failed once) since new and still operates flawlessly. The X weighs in at 3520 lbs for cruising, without ballast, and I use a Solas 4 blade 11.8 x 9 cupped prop to get 16mph at WOT per GPS.

[normo]

Most owners don't put a lot of time on an outboard so corrosion, FOD and aging may be equally or more important factors than power settings in determining engine life.

Running WOT for hundreds of hours has simply got to shorten life compared to an engines run at lower power settings. Manufacturers must know how much but they don't seem inclined to share this information.

[Don T]

Robert,
Yes, it returns to normal per se. I am still dinking around with the "boatability" (drivability) of the motor. It has never really been the same after that high speed run. Some will remember my threads from 2 years ago and last summer. But, I am a perfectionist and maybe I'm expecting too much from an 11 year old motor.

[Sloop John B]

Ive wondered about the efficiency of running at WOT.

I have a little river boat with the 25 Johnson kicker. Full throttle and its loud and vibrates everything a bit. I ease back on the throttle and it becomes quieter, doesnt vibrate, and Im going just as fast. I suspect Im using a little less gas.

The outboard instructions tell me to do this.

On the Mac, when I come off WOT a bit, the boat slows down. I would think getting up on plane as much as possible would be the more efficient posture. So, I dont know.

I like to run wide open on glass but when it starts getting a little choppy (like most the time) I ease back so my Mate wont loose her teeth.

[Helaku]

I worked for Detroit Diesel for a number of years in the engine test area where we dyno'd engines. More damage is done to internal combustion engines when they are run at low rpms as opposed to the high range. You have more fuel slobbering and carbon build up taking place. When the engine is in the higher rpm range it is operating at the temperatures it was designed for optimal performance and burning all waste.

Deny that and you are seriously fooling yourself.

I will leave those to argue if WOT in these outboards ever gets close to exceeding maximum efficiency. As most of these power plants have multiple hp ranges and the majority of owners are running 50 hp on plants that can be tooled for higher output, I seriously doubt that WOT is doing any damage and is probably running much more efficient than 2000 rpm.

[RHC]

Sorry to be out of touch, just crawled out of my cave:
what is WOT??

[Jeff Drumm]

Sorry to be out of touch, just crawled out of my cave:
what is WOT??

Wide Open Throttle.