W.O.T. as engine maintenance?

Ken O

Ken O

Member
I have long thought that the "wisdom" of running your motor full throttle was generally an excuse to go blasting around the neighborhood, or, at best, something needed to burn off oil residue in two-strokes. I rarely run my 90 hp Honda past 2,200 rpm, and it still runs smooth with 3 years on the same spark plugs. I recently saw a late model Merc 50 run rough and the shop advice was that it needed to run at W.O.T. frequently, and this advice seemed to work. Am I missing something here?
 
I purchased a 2007 25 cruiser with a Honda 150 a few years ago. The motor idled rough and the WOT kept declining. I took the boat to an independent marine mechanic and he couldn't find anything wrong...everything checked out ok. The following summer the motor ran worse I changed plugs and all the fuel filters...no improvement. So last year when I got the boat out of storage I took the boat to an authorized Honda Marine dealer. Again the motor checked out ok. The mechanic said they needed to get the boat on the water and do more testing. Lo and behold he said the motor had an excessive amount of carbon buildup due to the lack of not running WOT enough. The mechanic said that I had to promise him that I would run the motor at WOT occasionally and use Yamalube Ring Free Plus Fuel Additive. The Honda 150 ran great last summer! PS There were only 3 hours of WOT out of 1100 hours.
 
When we bought are Yamaha 90 the dealer said to drive it like you stole every once in a while to keep the engine running clean and we also use Yamaha ring free all the time. We have had no problems.
 
WOT every once in a while is solid advice. Engines are nothing more than air pumps that use a pretty dirty fuel to spin them. By running them up to max RPM for a short while, the engine is able to blow out a lot of the deposits that can affect performance, as well as get hot enough to burn off the layer of carbon at the top of the piston stroke. If you DON'T burn off that carbon at the top of the piston stroke, if one day you actually need full power, there is a possibility that the piston and or rings will interfere with that carbon ring and cause big problems.

Most of our engines now days are injected, which is great for a million reasons. Most injectors now days are inside the combustion chamber. Anything in the combustion chamber can and will form deposits, including the tip of the injector which can/will eventually cause spray pattern issues. Once your spray pattern is compromised, efficiency goes down, temps can go up or down, etc. By opening up the injectors all the way helps clean them off and improve spray pattern again. Especially with the occasional help of one of the best products ever: SeaFoam.

Clean fuel, WOT once in a while, clean oil is a winning combo.

Ever have a wood burning stove?

FYI I've been a professional mechanic/commercial pilot for over 30 years. Machines are my business.
 
Not really sure how many gas/diesel outboard/inboard engines I've had. Even
had one overboard, lost coming loose on a towed dinghy. Lesson learned.

I've learned other tips about engines. A lot of WOT is surely a mistake. So is
excess slow 'put, putting'.

Gas engines seem to like to run prolonged somewhere in the range of 60% WOT.
Diesels can run prolonged maybe close to 80% WOT.

Combustion engines like and work best over time operating at their "operating
temperature", as well as receiving routine maintenance. This means letting them
warm up some before jamming the throttle wide open. It also means varying the
throttle at appropriate times and places. It also explains why it is not a good idea
to "warm up" a cold winter stored engine a few minutes thinking you are doing
it a favor, being nice to it. In a few minutes, it won't have time to reach operating
temperature to remove/evaporate internal water.

If you treat'em right, they're usually good to you.

Aye.
 
I'll add my vote to the WOT periodically. Or for us regularly. Maybe not every day, be at least every other day when cruising for a few minutes. These motors are made to run at that RPM.

Granted that racing outboards are a different animal, but they are revved up to close to 10,000 RPM on occasion. I had a ride with Bill Seebold (Formula one boat guru, owner and driver, with a special 2 person boat. Carbon fiber surrounding the cockpit module area, with 5 point harness, pony bottle of oxygen, and rescue divers standing by). We hit 138 miles per hour and the outboard was near 10,000 RPM. The boats when racing can hit155 mph, with a 2.5 liter engine, hitting 10,500 RPM and HP close to 400. Bill said afterward, I have rarely had a rider wanting to hitting that WOT speed--My retort was that my thumb was stuck in the "UP" position, he kept pouring on the coal, as long as my thumb was up. These boats can go 0 to 60 in less than 2 seconds, and will pull several "G's" in tight turns. Enough that you are instructed to use the Valsalva maneuver (Anti G straining maneuver).
 
You can take what Foggy posted to the bank...The cruising boats we had diesels that WOT was somewhere in the low 2000 PRM, usually run at 1600 RPM. Each time I ran it for a day or so, we revved it up under load to. around 2000, fastest we ran it for longer period of time was 1800, but 3:1 gear ratio and big props. The Symbol MY had two 3208 cats NA, or about 210 hp each and max was 2800 WOT (As that engine was rated for light marine use. In some other uses the engine may be rated at 3200 RPM. We took the NA cats to WOT almost each time we went out, before we came into the "No Wake Zone"--where we basically idled at 5 knots. Every diesel from a Sabb 18 hp normally manual start 2 cyl, and an Albin, to a number of Perkins and Westerbekes for both generators, and prime power in racing sailboats up to 45 feet. Two RVs had Cummins C series at 350 hp, which was moderate turbo and after cooled. Some of the B series cummins 6.0 to 6.7 L rated NA at about 115 hp up as much as 375 HP which are rated entirely differently in a pickup truck. The NA diesels should last at least 10,000 hours. A friend had a Kabota in his 8 KW boat generator had 20,000 hours and still running well --one valve job and that was the extent of care other than routine oil and filters change.

Back to our C Dory outboard: We normally ran the Honda 90 or Honda 150 as fast as 5200 RPM, with a WOT of 6,000 RPM, if running heavy as in supplies for a month. As the fuel weight decreases and the food weight decreases, that same speed is available at 4800 RPM. In my dinghies we had outboard from 2 HP to 25 HP and we ran them at "what sounded right". We never wore one out. The outboard thrives on moderate RPM and consistent use. The ones with 10,000 hours are usually Coast Guard, Law enforcement, ferry type of boats. Daily use, much at lower speeds.
 
I haven't had my TC24 at WOT before. I like to cruise around at what seems to be max fuel effficiency (~19 kts, 3600 RPM) for us. Honestly, kind of been afraid to push it to all the way up. That fear (PTSD really) is based on an experience from my previous 'boat'...a Bayliner 2252 that I referred to as the 'Anti-Christ'...literally with engine pieces and oil flying around. I've been curious, but wanted to wait for a 'perfect day' to test it out...flat sea and light load. But from a maintenance perspective, it makes perfect sense to excercise the motors periodically. So my question (out of ignorance) is how do you know when you're at WOT? By the BF90D manual, its between 5300-6300 RPM...with a few factors affecting that. So is it a matter of hitting a physical hard stop on the throttle...or just getting to a point that additional throttle movement no longer results in RPM increase? Is it a slow approach to maximum...or will I get some sort of indication from the engine displays that I'm there?
 
With trim tabs neutral if you have them, the motor trimmed while at full speed to get the highest RPM (make sure your are in the manufacturer full throttle recommended high rpm specs. with your prop) at full throttle and maximum attainable speed (don't forget that trim for highest rpm), you are there. Sounds simple but you must take into account your load, water conditions and be especially watchful for floating debris. Be safe.

http://www.c-brats.com/albums/album3087 ... _30_Kn.mp4

I'm sure others will have much more to add.
 
Modern Outboards have a rev limiter, I believe in all motors. Depending on the specific motor and brand it can vary. The 150 and the 90 both seem to limit at 6,000 or slightly more.
 
High RPM usage is what outboards are designed to do. I have thousands of hours on my old Hondas and Yamahas where they run at 4k to 6k RPMs. Full throttle? Yes, every single trip I would say, but I don't usually run them at 100% for hours on end....except for maybe my Yamaha 40 on a skiff. But I do run them at 6k RPMs frequently. I understand we all want our outboards to last as long as possible. What I have found is as long as you operate them within the parameters they were designed, they will last a really long time if you provide the basic care they need.
 
I was raised with the old set-up of marinized gas v-8s--mostly Chrysler 318 blocks--reverse gear and straight shaft and prop. Common wisdom was to not run them wide open. They were not designed to run under a load all the time anyway. Most of these engines were raw water cooled and rusted out pretty quick in salt water anyway, but 1000 hours in a boat was a healthy lifetime. As a result, I was always shy to run any boat wide open, until my buddy who ran a boatyard explained that outboards were designed to run under load continuously, and, as others have said, run better and cleaner if opened up regularly. That is my practice now, although I don't find a C-dory 22 very pleasant to run above the mid-twenties. Consider it medicine. Sam
 
qboat":1l5t4908 said:
I was raised with the old set-up of marinized gas v-8s--mostly Chrysler 318 blocks--reverse gear and straight shaft and prop. Common wisdom was to not run them wide open. They were not designed to run under a load all the time anyway. Most of these engines were raw water cooled and rusted out pretty quick in salt water anyway, but 1000 hours in a boat was a healthy lifetime. As a result, I was always shy to run any boat wide open, until my buddy who ran a boatyard explained that outboards were designed to run under load continuously, and, as others have said, run better and cleaner if opened up regularly. That is my practice now, although I don't find a C-dory 22 very pleasant to run above the mid-twenties. Consider it medicine. Sam
Click to expand...

I remember those...and a ton of 305s, 350s, and others. They really were good engines in my opinions. However, like you noted, 1000 hours was getting up there. I saw lots of them fail way before that. For the most part, it wasn't because of the engine itself, but because something bolted to them failed and let water in. Or the lower drive just gave up the ghost. Small and mid-range outboards are a different animal.
 
Back
Top