HOW LONG TIME WOT?

[CARLOS]

I WOULD LIKE TO KNOW, HOW LONG TIME CAN I KEEP RUNNING MY ENGINE AT WOT?<br />THIS QUESTION IS FOR THESE GOOD CONDITIONS ENGINES:<br />MERC 4HP 1990<br />MARINER 275HP 1992 (COSWORTH)<br />MERC 200HP 1992<br />ALL THESE ENGINES CAN BE WOT FOR LONG TIME?<br />IF YES, ANY SPECIAL CARE? ANY SPECIAL ENG. OIL BRAND OR OIL MIX. LIKE 30:1?<br />OTHER GUY TOLD ME THAT MY 275 HP MARINER IS A STRONG LADY?<br />(KEEP WORKING ALL DAY BUT AT LOW-MED 4000 RPM MAX)<br />THANKS<br /><br />SALUDOS DESDE VENEZUELA<br /><br />CARLOS

 

[Jack Shellac]

Re: HOW LONG TIME WOT?

Generally speaking, if the engine is operating within it's recommended RPM range, you can run at WOT indefinitely. Not that I think it's a good idea, myself. As far as oil, use the engine manufacturer's recommended brand and mix. Watch temperature closely and listen for alarms.

 

[dkondelik]

Re: HOW LONG TIME WOT?

I agree completely with Mr. Shellac.<br /><br />If you don't have a tachometer(s) on your motor(s) it might be a good idea add. The manufacturer, will spec operating rpm rang for their motors. Keep the rpmcomfortably within the range and you ought to be just fine.<br /><br />Good Luck<br />HAVE FUN!<br /><br />P.S. Do you really run your 4hp Merc at WOT for long periods of time? Is this motor "fixed" on one boat? Is it primary power, troller, back-up? The reason I ask is that the answer will have a strong influence in if/how to mount the tach.

 

[Kenny Bush]

Re: HOW LONG TIME WOT?

Carlos, that is a tough question, but I do not think anyone wants to continually run wide open throttle all of the time. However I would reccomend that all motors be run wide open for at least 5 minutes for every hour of use. THis will keep it blown out. Most people run their motors at the best power/rpm zone for economy. As said earlier, the manufacturers state the operating RPM range that the motor should operate. When I settup my boats, I choose power options that give me that "Zone" at about 60% throttle. Goodluck, BushCat

 

[FlyBoyMark]

Re: HOW LONG TIME WOT?

Do not exceed the maximum amount of recomended oil...the engine will be run in a lean condition and will over heat. Remember...your displacing fuel, which also keeps the engine cool, with non combustable oil. The jets or carbs/injectors regulate only a given total fluid. Thats why the manufacturers recomend you DO NOT run the engine at WOT except for very short periods untill the engine is fully broken and have returned to standard fuel without additonal oil.

 

[Forktail]

Re: HOW LONG TIME WOT?

Sorry FlyBoy, I have to disagree with you. <br /><br />First, a slight oil-rich mixture will displace such small amounts of fuel that it's hardly worth mentioning. The outboards originally posted in this thread have no need to run richer than what is recommended anyway, WOT or not. <br /><br />Second, 2-stroke oil is combustable (its high volaitlity is what sets it apart from other motor oils), and it will act very similar to fuel (if not better) in terms of cooling the cylinder. I would only suggest running a good TCW3 oil.<br /><br />Finally, the break-in period will specify avoiding lengthy WOT periods because engine parts like bearings and rings are in critical stages of wear when they are new. Putting new mating parts under large stresses (WOT) before they get a chance to "mesh" is not good. Avoiding WOT on a new outboard has nothing to do with lean fuel mixtures or overheating. It has to do with ruining mating surfaces like bearing journals, etc.<br /><br />These outboards are said to be in good condition and they are obviously broken-in. They are all designed to run at WOT until the cows come home. Some of my best running Yamaha's have seen nothing but WOT since day one.

 

[SpinnerBait_Nut]

Re: HOW LONG TIME WOT?

I was just going to add, that I had one of them Cosworth motors and that is the only way it knew to run, WOT. <br /><br />Seriously though, it seemed to run better that way than trying to run 1/2 or 3/4 thottle for some reason.<br /><br />It would load up easy at times of slow speed and that is one reason I got rid of it.<br /><br />Good motor though as far as running.

 

[Skinnywater]

Re: HOW LONG TIME WOT?

Right or wrong, I'm a firm believer that asking for all she's got(100%)constantly is being up against maximum all the time and is pushing it.<br />Being at 90-95% constantly is'nt, and is nearly the same result. <br /><br />I'll get to speed at max. RPM and back off 500 RPM.

 

[Skinnywater]

Re: HOW LONG TIME WOT?

Unless I'm running for my life or money.

 

[G DANE]

Re: HOW LONG TIME WOT?

When I had my Volvo I/O the users manual said:<br /><br />"No good captain will during longer cruises exceed 80 % of full power permanently". But that was a 4 stroke.<br /><br />I guess 2strokes arn´t that different though.

 

[Forktail]

Re: HOW LONG TIME WOT?

Actually, CARLOS' three outboards are all carbureted 2-strokes. Carburetors can't meter fuel perfectly throughout the entire throttle range. There are usually hot (lean) and cold (rich) spots where jetting goes from the pilot circuits, to the midrange circuits, to the main circuits. This is especially true for butterfly-type carbs. Therefore, there will be particular throttle positions (usually in the midrange) where the cylinder temperatures will actually be higher than at WOT. At WOT all circuits are wide open and the cylinder is receiving maximum fuel. It is not uncommon for outboard engines to detonate at midrange when the fuel is between circuts and the engine is using more air. My experience is that most outboard seizures happen at reduced throttle, not WOT. <br /><br />Just because an outboard is designed with a maximum rpm operating range doesn't mean this maximum is at 100% of "what she's got". One trait of an outboard is that it's designed to run thousands of hours withing it's operating rpm range. Several outboards of exact same engine displacement can vary in maximum rpm between models. An example could be Yamaha's 1730 cc 115 hp 2-stroke that runs max at 5500 rpm and their same 1730 cc 130 hp 2-stroke that runs at 6000. I sure there are many other examples.<br /><br />Running an outboard at reduced rpm can actually cause more stress on the engine. Aside from possibly higher cylinder temps, the engines aren't designed to bog or lug under load. Although if you have plenty of power, there is nothing wrong with an economical cruising rpm (but I doubt it will make your engine live longer). <br /><br />G DANE, inboard/outboard marine engines are designed completely different than outboards.

 

[SCO]

Re: HOW LONG TIME WOT?

It's good to have you on this board Forktail. You used to put me off , and I still take your posts with some skepticism(like I take all posts), but you have a lot of experience and knowledge, and I like getting your take. Thanks.( DJohns, I like your takes too). I'd now like to get a plot of engine temp as a function of rpm. We should be able to plot the best rpms to run the engine. But it is a safe bet that the engine would be able to run ok by design at WOT, as you have verified empirically.

 

[CARLOS]

Re: HOW LONG TIME WOT?

OK,OK,OK,<br /><br />THANKS TO ALL OF YOU...<br />VERY INTERESTING COMMENTS THAT I´LL TAKE IN MIND.<br />KLONDIKE 7: MY MERC 4HP IS RUNNING IN A 2.6M DINGHY. SOME TIMES I USE AT WOT WHEN I´M ALONE.<br />ANYWAY, THANKS TO EVERYBODY FOR COMMENTS<br />(I LOVE MY 275 COSWORTH MORE THAN MY GIRL FRIEND...)<br /><br />THANKS<br /><br />CARLOS