Running WOT

pstew96

pstew96

Active member
Member
Joined
Dec 4, 2003
RO Number
12527
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727
How long can a boat run WOT before you need to be concerned about ruining the engine? I blew my engine last week, a perfectly maintained engine, I WOT to get up on plane and I need to mess with the trim tabs to get it up sometimes. Then I like to see how fast I can get it, but I don't maintain WOT for very long. I'd really like to know why this engine with 125 hours on it blows up!
 
How did it blow up? Top end, bottom end, both, water ingestion, or you don't know? In general, you don't want to operate at WOT any longer than a test. So I wouldn't want to run my 4600 WOT spec any longer than a prop test requires. I actually baby mine and choose to never go above 3800.
 
WOT operation shouldn't hurt anything and I do it just to test that everything is working as it should. That being said it is also a challenge to Murphy's Law "if anything can go wrong it certainly will". How long is it safe to run at WOT my opinion is a minute to two should not cause any problems. The recommend WOT of my boat is 4400-4800 rpms and the rev limiter is a little higher. The beginning of the season I can usually hit 4800 or a little more but as the season progresses I lose a little at the top. If your engine failed at 125 hours it wasn't because you hit WOT it was because of a failure somewhere in the engine, I would focus on what failed and try to prevent it from happening again. One more thing you should be able to run an engine at up to 75% of WOT rpm all day long without causing any problems.
 
Need more info.
Type of motor.
Make of boat.
Age of motor.
Maintenance done.
125 hours would be like a 3 year old motor, if it's older than that, then it's not getting enough usage and that could be a point of failure.
If oil changes not done or wrong type of oil used.
Did it ingest water.
Was it over-heating at the time?
 
Other than pulling up a big slalom skier , going WOT to attain plane is about as max stressful on engine bearings and other engine and gear internals as anything you can do to it. I'd venture if you need WOT to get on plane it is underpowered, over propped or trimmed/tabbed very wrong. I'll suggest you extend tabs & trim drive down BEFORE applying throttle for better results.

Once on plane ( which takes about 3 secs at 1/2 throttle with tabs deployed considerably on my gas I/B boat), even to test on rare occasions, I wouldn't run WOT for more than a minute if it takes that long to confirm it won't reach higher RPMs .

As Brite Idea notes, the engine mfgrs. generally spec 75% of WOT as max cruise speed. Everything critical to a marine engine becomes a lot more critical at WOT than at lesser cruise-level throttle positions. You need a LOT more RW , oil, fuel and air flow .

Consider running your car or truck on the highway using only 2nd gear for an extended period so the rpm are equal to your boat WOT RPM. And that would be with a whole lot less work load than your boat engine experiences.

If your engine is injected , a marine scan device should be able to access the number of hours run at each 1000 rpm increment.
FWIW- With over 2100 hrs on my latest(2003) I/B's, I believe the 4000-5000 increment has not registered an hour yet.

125 hrs is less than a typical NE recreational boating season for me. I wish it was a lot more .
 
Did your engine reach designed wot rpms? Or were you just running it overloaded at the highest rpm you could achieve. Needing to hit wot just to get up on plane, is in itself a form of lugging. What failed? "Blew up" is an ambiguous statement.
 
Must be more to the story. A properly maintained and properly loaded engine does not blow up at WOT for short or even moderate periods.
 
Ok, so my mechanic says that was my connecting rod in my oil tank, he says its difficult to predict when or why this happens, could be because of lack of use (I though it was good to buy a boat with low hours) long periods of no lubrication being spread about the engine. He also said that some boats are sold under powered just to make them affordable. So, I'm replacing the motor with a 383 Stroker at 300 hp and like Stephen, I'm gonna baby it!
 
Lack of use, boats that sit are a red flag.
Gaskets dry out, hoses dry out, metal rusts and creates more tension by resting in the same spot.
Even running a motor now and then helps if the boat doesn't move.

As for a WOT debate, I think motor is meant to handle it Overpowering your boat may create different issues.
Your weight distribution may be off so you may find you can't plane at certain speeds. Check the weight of new motor against the old. You will also burn way more fuel. So before you just buy a big a** motor you may want to make sure your boat can handle and perform with it. There is a reason manufacturer's limit the choice of motor's in their boats!
 
quote:
Originally posted by pstew96

Ok, so my mechanic says that was my connecting rod in my oil tank, he says its difficult to predict when or why this happens, could be because of lack of use (I though it was good to buy a boat with low hours) long periods of no lubrication being spread about the engine. He also said that some boats are sold under powered just to make them affordable. So, I'm replacing the motor with a 383 Stroker at 300 hp and like Stephen, I'm gonna baby it!

Click to expand...


Are you sure you are getting a stroker? 383's normally run between 320 to 440 HP.
 
Yes, this boat comes with an option for a 5.7, this motor is about the same size and weight but it going to be the Alpha version. Thats why its 300hp.
 
When the new engine is broken in properly make sure the prop is correctly sized so that you can reach WOT. This is critical to the long term survival of your engine. Also there is no benefit of babying your engine, if it's propped correctly running it like you want won't hurt it. Also think about FWC if your planning on keeping the boat for a long time. Good luck with the new engine.
Rob
 
Before you spend $$$ on a new engine, make sure that everything continues to fit in the old space. Make sure the mounts, trans, starter, accessory belts, etc fit. Otherwise, your replacement may not be as good of a deal as you thought. Also, I wouldn't put the extra $$ for the stroker with high HP. You didn't say I/O or I/B, but if you go with more than moderate higher HP, you will have to re-prop. Personally, I would consider dropping in the less expensive 5.7.

Also I have to explain the "babying" aspect. I have my prop tuned specifically for the range I want to run and chose the 2 barrel carb on purpose to maximize fuel economy. So my babying is actually just a good formula worked up for my boat where I can just reach the lower WOT spec. You might not be able to do the same with yours because you may not have the clearance for a larger prop.
 
I was gonna ask what Rob mentioned. Was the engine broken-in using proper procedures?

The harshest thing you can do to an engine is slam it to full throttle from idle.
 
just to clarify running an engine that only makes it to the bottom end of the specified WOT range is lugging and will actually shorten the engines life. If you want the best performance and longest engine life it should be propped to reach maximum rpm called for by the manufacturer. I'm not saying to run WOT all day long I'm saying the engine must be able to reach the high end of the specified WOT rpm so that it is working optimally throughout the engines power curve.
Rob
 
Yes, that's what the last engine did, I was at the very lowest of my RPM range at WOT, 4100 rpm rated is 4200-4600 this boat sat unused for long periods, but last year when I got it, I put 60 hours on it and it was fine, something happened while sitting in a warehouse over the winter. The only thing I did over the winter was install a small TV. Yea, these guys at Bergen Point put the same engine in my other boat 245 Sea Ray and it performs flawlessly... I generally use the boat 3-4 times a week.
 
quote:
Originally posted by Brite Idea

just to clarify running an engine that only makes it to the bottom end of the specified WOT range is lugging and will actually shorten the engines life. If you want the best performance and longest engine life it should be propped to reach maximum rpm called for by the manufacturer. I'm not saying to run WOT all day long I'm saying the engine must be able to reach the high end of the specified WOT rpm so that it is working optimally throughout the engines power curve.
Rob

Click to expand...


I disagree. Reaching the low end of the WOT specs is not lugging. It's, well, reaching WOT. I have 16 years on the same engine that proves it. Would you suggest that reaching the high end of the range is underpropping?
 
quote:
Originally posted by pstew96

Yes, that's what the last engine did, I was at the very lowest of my RPM range at WOT, 4100 rpm rated is 4200-4600 this boat sat unused for long periods, but last year when I got it, I put 60 hours on it and it was fine, something happened while sitting in a warehouse over the winter. The only thing I did over the winter was install a small TV. Yea, these guys at Bergen Point put the same engine in my other boat 245 Sea Ray and it performs flawlessly... I generally use the boat 3-4 times a week.

Click to expand...


You put 60 hours on it. Did it have the 125 hours total? How many years old was the engine? Is it possible you had water back up past the exhaust manifold? That can definitely cause a failure.
 
Something big is missing here. Everything was perfect but the engine threw a rod. Does not happen!. I cant remember anyone in all the BE history reporting a lower end failure. Top ends fail but bearings just don't fail without a lubrication problem or significant over loading.
 
I have a friend that owns his own auto shop and runs more hours than I do, (300+ hrs/yr) He has a 351 w in a 1977 searay 240 with about 1400 hrs and threw a rod through the block. It was a pleasurecraft motor. FWC

That was only the second I've ever heard of, too.

That usually happens when over reving or the bearings/engine getting pretty worn out
 
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