WOT, how long is too long to keep 'er pinned?

[haulnazz15]

Re: WOT, how long is too long to keep 'er pinned?

My concern about WOT isn't as much the engine as the outdrive. Run at normal cruise for 10 minutes and then check the temp of the outdrive (IR thermometer, please). Then go run for 10 minutes at WOT and check the outdrive temp, the temp difference will be significant on most outdrives that don't have a cooler or drive shower (most of them). We all realize the WOT is not "redlining" per say, but the load on the engine in a boat @ 5K rpms is probably more than the load on that same engine in a car at 6K rpms.

I also disagree on WOT being needed for correct plug maintenance for a 2-stroke. Correct air/fuel mixture in the carb at all throttle positions is responsible for that, as well as prolonged idle as most idle settings are a bit on the rich side. If you need WOT to keep your plugs unfouled, you need to see about adjusting your carb to lean it out.

My lawnmower doesn't run at redline, it runs at a predetermined WOT speed, just like a boat. My trimmer generally doesn't see more than 50% throttle unless I'm using the edger attachment, then it gets 75-80% for a minute or two. The blower probably sees the most full-throttle usage, but it's only held there for 15-20 seconds at a time.

 

[soggy_feet]

Re: WOT, how long is too long to keep 'er pinned?

Good examples there. Lawn mowers are run full throttle their whole lives and are mistreated by 99% of all owner's. They are lugged(mowing tall grass to fast) often and operate in very warm weather. Not many people EVER change the oil in them either.

wait.... lawnmowers have oil?





Only time i've ever done damage to a 2-stroke from WOT was riding a dirtbike up a dirt road after the boot between the air filter and carb slid off. Think it ate a stone, broke some rings, scored up the piston.

I think the real issue is whether you're WOT with load on the engine or not. I'll happily run my car near WOT ice racing in the winter for 20 minute sessions, but I cringe at the idea of opening the throttle up like that for even a minute with the car in neutral.

My concern about WOT isn't as much the engine as the outdrive. Run at normal cruise for 10 minutes and then check the temp of the outdrive (IR thermometer, please). Then go run for 10 minutes at WOT and check the outdrive temp, the temp difference will be significant on most outdrives that don't have a cooler or drive shower (most of them). We all realize the WOT is not "redlining" per say, but the load on the engine in a boat @ 5K rpms is probably more than the load on that same engine in a car at 6K rpms.

But, my car, quad, and that old dirtbike i mentioned didn't have oil coolers on the transmissions/differentials either, and they've fared well enough.


Although, car, boat or bike, all applications are different. Even boat to boat, there's too many variables to get a solid argument for/against WOT runs.

 

[Thalasso]

Re: WOT, how long is too long to keep 'er pinned?

if it is an i/o the outdrive may get too hot unless you dunk it or drive shower.

How is the outdrive going to get to hot. It's submerged in water. Under this pretense so would an o/b

 

[Thalasso]

Re: WOT, how long is too long to keep 'er pinned?

would you run your chainsaw or weed wacker at half throttle, how bout your leaf blower? i run my 2 strokes full trigger. they were designed for it, some 4 strokes too. ever run your mower set to the rabbit for an hour? i do every other week. it only matters when there is no load to keep it from over reving and the redline is exceeded things will fly apart throwing rods and such

Run them for hours on end at full throttle like the op's statement and see what happens. They won't last as long.

 

[Alumarine]

Re: WOT, how long is too long to keep 'er pinned?

Dig into the Boat Engines Manufacturers recommendations and you will find 70% throttle recommended for extended use with five minutes at WOT allowed occasionally.

I just read the operating manuals for my 1974 3.0 Mercruiser 4 stroke I/O and my 1981 Mercury 50hp 2 stroke.

For the Mercruiser, other than the break in period, the manual makes no mention of limiting full throttle operation.

For the Mercury, it only says "sustained operation at full throttle should be avoided for an additional 8 hours" (after a 2 hour period of lower rpm operation for break in.

My smaller motors have been used at full throttle all summer for 30 years.

 

[UncleWillie]

Re: WOT, how long is too long to keep 'er pinned?

How is the outdrive going to get to hot. It's submerged in water. Under this pretense so would an o/b

Everything above the Anti-Ventilation plate is above the water when on plane.
That is why Drive showers are available to cool the The Upper Units of I/O's

Outboards do not have Upper Units to make that second 90 degree turn.

 

[Thalasso]

Re: WOT, how long is too long to keep 'er pinned?

I just read the operating manuals for my 1974 3.0 Mercruiser 4 stroke I/O and my 1981 Mercury 50hp 2 stroke.

For the Mercruiser, other than the break in period, the manual makes no mention of limiting full throttle operation.

For the Mercury, it only says "sustained operation at full throttle should be avoided for an additional 8 hours" (after a 2 hour period of lower rpm operation for break in.

t)

My smaller motors have been used at full throttle all summer for 30 years.

For hours on end??? ( referring to op's statement)

 

[Thalasso]

Re: WOT, how long is too long to keep 'er pinned?

I just read the operating manuals for my 1974 3.0 Mercruiser 4 stroke I/O and my 1981 Mercury 50hp 2 stroke.

For the Mercruiser, other than the break in period, the manual makes no mention of limiting full throttle operation.

For the Mercury, it only says "sustained operation at full throttle should be avoided for an additional 8 hours" (after a 2 hour period of lower rpm operation for break in.

My smaller motors have been used at full throttle all summer for 30 years.

Edit: Duplicate

 

[Thalasso]

Re: WOT, how long is too long to keep 'er pinned?

Everything above the Anti-Ventilation plate is above the water when on plane.
That is why Drive showers are available to cool the The Upper Units of I/O's

Outboards do not have Upper Units to make that second 90 degree turn.

:redface::redface::redface: Forgot that. I wasn't thinking. Just picturing the drive setting in water.

 

[metriccrescentwrench]

Re: WOT, how long is too long to keep 'er pinned?

Guy at work, resident boat genious. He says he tools around an area lake at WOT for an hour or more. I say he's doing long term damage, he says their made for it. Guy kind of gets under my skin anyway so mostly we argue because thats what we do but who's right?

EVERYONE, I've seen posts on this thread about 2 strokes, I've seen posts about outdrives, but I never did see a post about whether the boat in question had an outboard or I/O, much less what size engine and what size boat.

For my money, I'm betting the guy is full of crap. If it's a boat/engine combination of any size he probably can't afford the gas to run it like that. For instance, I estimated it costs me about $1.50 per MINUTE to run my Checkmate at WOT - ain't no way in heck I'm going to spend that kind of money.

 

[Tagerman]

Re: WOT, how long is too long to keep 'er pinned?

My .2 My boat has what I would consider a sweet spot at about 3100 rpm (on plane, motor is quiet, just cruising). The only time I run it WOT is when I'm trying to pass some jack*ss zig zagging through the channel or cutting a corner to get around the wake of a Gibson house boat kicking out 4 foot swells at full tilt. I think the longest I ever ran it at wot was for 20 minutes on the test drive because my theory is if you don't trust it to have the crap driven out of it for 20 minutes then its not in good mechanical condition.

 

[BoatDrinksQ5]

Re: WOT, how long is too long to keep 'er pinned?

Direct quote from a 2010 Mercruiser O&M Manual:

After Break‑In Period
To help extend the life of your Mercury MerCruiser power package, follow these recommendations:
? Ensure that propeller allows the engine to operate at or near the top of the specified WOT RPM range. Refer to
Specifications and Maintenance.
? Operate the engine at 3/4 throttle or lower. Refrain from prolonged operation at wide‑open‑throttle RPM.

Follows some common sense IMO - so i suppose i will heed it and my common sense.

 

[Howard Sterndrive]

Re: WOT, how long is too long to keep 'er pinned?

I have a 1975 Evinrude 25, and a 1975 Evinrude 20
they are both 22 cid twins, identical in every way except carb and reeds

the 25 has a WOT recommended at 5000-6000 rpm - it is propped for WOT of 5350*
the 20 has a WOT recommended at 4000-5000 rpm - it is propped for WOT of 4100*

*same prop actually

anyone going to suggest I can't run that 20HP at it's WOT 4100 rpm it's entire life?
I don't see how it would be any different than running my 25 at 76% of max rpm...

point is - depends what motor the guy has

I used to have a 1.2HP outboard... if you didn't run at WOT, it didn't do anything .... might as well toss it overboard

 

[CoffeeHound]

Re: WOT, how long is too long to keep 'er pinned?

Guy at work, resident boat genious. He says he tools around an area lake at WOT for an hour or more. I say he's doing long term damage, he says their made for it. Guy kind of gets under my skin anyway so mostly we argue because thats what we do but who's right?

There are NO right or wrongs -- just missconsptions --- and one i love the best is WOT, which by the way , is NOT REDLINE but usually top rpm, in gear on the lake with the throttle handlle full forward under normal load. WOT is the center top of the graphed power curve. Any higher RPM than factory recommended WOT is where you put the moter into stress and high wear, and Yes you can blow the motor to kingdom come. Quality oil and clean fuel should let the motor run forever at or near WOT,, or at least still be running after you are long gone to this world .

 

[jestor68]

Re: WOT, how long is too long to keep 'er pinned?

Guy at work, resident boat genious. He says he tools around an area lake at WOT for an hour or more. I say he's doing long term damage, he says their made for it. Guy kind of gets under my skin anyway so mostly we argue because thats what we do but who's right?

You are the winner. You co worker is apparently totally ignorant concerning how wear takes place in any engine.

 

[Alumarine]

Re: WOT, how long is too long to keep 'er pinned?

For hours on end??? ( referring to op's statement)

For the smaller motors certainly several hours a day at WOT when they're used.
Only lost motors due to neglect.

 

[Alumarine]

Re: WOT, how long is too long to keep 'er pinned?

Direct quote from a 2010 Mercruiser O&M Manual:

After Break‑In Period
To help extend the life of your Mercury MerCruiser power package, follow these recommendations:
• Ensure that propeller allows the engine to operate at or near the top of the specified WOT RPM range. Refer to
Specifications and Maintenance.
• Operate the engine at 3/4 throttle or lower. Refrain from prolonged operation at wide‑open‑throttle RPM.

Follows some common sense IMO - so i suppose i will heed it and my common sense.

I guess the older motors were built better and the engineers had a different "common sense".

 

[Vegas Naturist]

Re: WOT, how long is too long to keep 'er pinned?

Just my $.02. In a perfect world (well maintained engine and outdrive, correct prop), you're really not going to hurt it significantly by running WOT for extended periods, but why would you want to? On my 3.0LX my sweet spot is about 3800 RPM. Trimmed correctly and on good water this gives me about 35 MPH on the speedo. When I run it up to 4600 RPM (WOT on my boat), I only get +/- 40 MPH (increased prop slip?). In other words, the increase in RPM's doesn't give me much of an increase in speed, but certianly increases fuel consumption. Also, I prefer to have some reserve throttle in case I need to take evasive action to avoid an "India Delta Ten Tango".

John

 

[TTavenier3]

Re: WOT, how long is too long to keep 'er pinned?

this is a option based issue. just fyi. lawn motors chain saws, weed wakers.ect are carberated. not fuel injected. there is no governer or wot restricor. there is just open and close. unless you own a fancy john deere or hi end lawn mower there is no engine govener. most boat motors are the same way. if there carberated then they are not governed. as for your question about wot hurting the motor when held for long periods of time. well yes and no. when manufactures make motors they are ran at wot or a performanced estimated max rpm for an extended life cycle run to test these motors. i worked for a motor company in florida. we did it all the time.
but on the flip side. running a motor at w.o.t will cause extreme heat. which will weaken metal making the life of the parts shorter because of what we call heat cycles soften the metals. and not running a motor at w.o.t can cause problems too. weather you run 2 motors next to each other one a wot and one a half throttle one may run longer than the other but unfortionitly there is not an experation date or hour date that they just stop working. so its unknown. either way you go or either thing you do is your choice. as long as you maintain your motor everything will be the same

 

[V153]

Re: WOT, how long is too long to keep 'er pinned?

Personally I wouldn't run an IO above the suggested max operating rpm for more than a minute or two. 'Less it was built for it. As previously mentioned outdrives can get purty hot. But if it's an OB? Ehh, that's a different story. I prop mine to max out 2-300rpm above OMCs recommended operating range. Routinely wind my V4s up to 6200 or so, briefly. Clears the cobwebs out ...

Guess it boils down to what your objective is. If you're in the midst of blowing off some wanna be speedracer, then by all means keep the hammer down. If you're cruising try to find a prop that'll let you cruise somewhere around 30mph @ 3000rpm. That's a magic number. If ya wanna tow stuff the rules change yet again.

But I digress