How long can you run at WOT

C

CDA205SP

New Member
Oct 10, 2011
13
CDA, IDAHO
Boat Info
2011 205 SP
Engines
4.3 MPI
Hello. First post on this board. Just bought a '11 205 Sport with 4.3 MPI. Does anyone know how long you can run this engine at wide open throttle safely after it has been broken in? I could not find anything on the Mercruiser site and I searched the forum here with no luck.

Do you ever run at WOT and if so how long?

thanks
Derek
 
CDA205SP said:
Does anyone know how long you can run this engine at wide open throttle safely after it has been broken in?
Click to expand...

The question might be why? Congratulations on your choice of boat, btw.

I would swear that I saw in my Mercruiser a comment - no explantion given- to avoid long WOT.

You have a great boat, but it is heavy, and you have the absolute base powertrain for a 21' Sea Ray. My carbed V-8 has the same 220 hp you have, maybe a little more torque. Properly tuned, they should perform about the same.

The 205 is great value in a roomy 21' boat, but won't set any speed records. On glass smooth water, light load, and parachute (bimimi) down, I can creep toward 40. I think top speed is rated about 43. It's not important to me, I don't really recall.

Under a full family load in light chop I'll be darn near WOT @ 30-35. I hold it back some to reduce stress on the powertrain.

You have a nice family bow-rider cruiser that will do water sports very well fine if you don't feel the need for speeds over 30 on a sustained basis. I think most of my tubes are safety rated to about 15, and skiing over 20 is usually too fast for me. Pro skiier's - I think, don't go much over 35.

Enjoy in moderation!
 
I was just wondering because I owned an I/O about 20 years ago and the rule then was that you didn't run WOT for long periods over about 5 minutes. 2 stroke outboards you could run all day at WOT. With the new technology fuel injection and 6 cylinders I was wondering if things have changed and maybe you can run WOT for longer periods and not harm the engine.

I'm surprised that you are getting the speeds you mention. I had the choice of the 205 sport with a 5.0 MPI with cat (260 hp) and the 4.3 MPI no cat 220 hp. I lake tested both and I was very impressed with the 4.3 MPI. Didn't have to fight the throttle to keep a good wake for wake boarding which was not the case with the 5.0. The 4.3 ran top speed of 51(by gps) @ 4600 RPM with 4 adults and 2 kids on board and 1/2 tank of gas. It had 3 blade stainless prop not sure of pitch or size. The 5.0 ran a faster top speed but didn't hold mid-plane well and the 4.3 seemed as fast or faster out of the hole.
 
I read an article somewhere when Mercury tested the 350/260hp 4bbl merCruiser package it was run wide open 24 hours a day for a week with only stops for fuel and drivers. The hotter the oil got the better it ran. I'm not sure the 4.3L or 7.4L were ever tested like that. The Chevy 350's just seem to last forever. I have a 5.7L and 7.4L and run them at 3800rpms for most long runs.....4600 is their WOT, Mike.
 
Thanks for the replies. I had heard that you could run newer engines at WOT for 30 minutes and that mercrusier backs it up. As long as you are running under the rev limiter max rpm you are safe as far at they are concerned. Not sure if this is just a rumor. Maybe I will give them a call and ask.

I am not really looking to do this but I was just curious.
 
Running around idling all the time for an engine is not good for it. Running it on plane at 75% of WOT is typical and is how most of these engines are setup to run. Go-Fast boats that run hard rarely if ever get 2000 hours on an engine. Whereas boats that are babied and maintained can get that many hours or more. Is there maybe an issue with how your boat is propped so it is not performing properly? What is your WOT?
 
Some may not agree with this but Mercruiser says their power curve data is proprietery info and will not release it. At wot throttle you are running at max hp to torque ratio the rev limiter lets you go a couple hundred rpms over that. Would really like to know what the dyno readings are on most mercruiser engines just to see how there setup. Without knowing that data it is all guess and try for your engine and hull to achieve best performance for your needs.
 
Dave 205;518491 You have a great boat said:
How are you getting your readings GPS or speedo? I get 51 on the GPS with a 19" Vengeance at 4900 RPM's. I ran a 21" Vengeance and got to 54 GPS at 4650 RPM's. The tach isn't graduated so those are approximate numbers. Dave you should be getting closer to 48 or 49 wide open. I agree the 5.0MPI is slower out of the hole especially propped for speed. I prefer the 4.3 MPI for the single point drain and no catalyst. The difference in performance isn't worth the extra $3000
Click to expand...
 
CDA205SP said:
I was just wondering because I owned an I/O about 20 years ago and the rule then was that you didn't run WOT for long periods over about 5 minutes. 2 stroke outboards you could run all day at WOT. With the new technology fuel injection and 6 cylinders I was wondering if things have changed and maybe you can run WOT for longer periods and not harm the engine.

I'm surprised that you are getting the speeds you mention. I had the choice of the 205 sport with a 5.0 MPI with cat (260 hp) and the 4.3 MPI no cat 220 hp. I lake tested both and I was very impressed with the 4.3 MPI. Didn't have to fight the throttle to keep a good wake for wake boarding which was not the case with the 5.0. The 4.3 ran top speed of 51(by gps) @ 4600 RPM with 4 adults and 2 kids on board and 1/2 tank of gas. It had 3 blade stainless prop not sure of pitch or size. The 5.0 ran a faster top speed but didn't hold mid-plane well and the 4.3 seemed as fast or faster out of the hole.
Click to expand...


I don't know several things with certainty - but I likely have the same prop, and basically the same boat, yours has some interior updates that began in 2008. I know my 5.0 (305) is basically the same 305 small block that I ran in my mom's 1978 Caprice. I think the 4.3 is a two cylinder chopped 5.7 (350) that was dropped in a bunch of small trucks and some full size GM cars starting in the early 80's. At heart, these are old engines with new tech tacked on. I fried an Olds 307 at WOT in high school.

Enough history - my Mercruiser manual recommends that afer break-in: "Operation at 3/4 throttle setting or lower is recommended. Refrain from prolonged operation at WOT RPM."

Mine may be a little bit of a dog, but it starts and runs smoothly, and has a hole shot that works for me. I bought it barely used in the spring, and still haven't sorted out where the PO was at with it, he probably did nothing. So, maybe a tune-up will give me a surprise in the spring. You are right, it should break 50 according to this Boattest.com reveiw:

http://www.boattest.com/boats/boat_video.aspx?id=965

Load, and water conditions have a lot of impact on my boat. I almost always start with a full tank, I have a tube on board that weighs 50lbs. by itself - a lot of stuff accumulates on board. When I have a smooth lake to myself, the boat gets an extra 5 mph at any throttle setting over consistent wind or boat chop.

The 21' Select series boats in the era of my boat had options going over 300hp, I'm sure for a reason.
 
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blaster said:
How are you getting your readings GPS or speedo? I get 51 on the GPS with a 19" Vengeance at 4900 RPM's. I ran a 21" Vengeance and got to 54 GPS at 4650 RPM's. The tach isn't graduated so those are approximate numbers. Dave you should be getting closer to 48 or 49 wide open. I agree the 5.0MPI is slower out of the hole especially propped for speed. I prefer the 4.3 MPI for the single point drain and no catalyst. The difference in performance isn't worth the extra $3000
Click to expand...

By speedo. I probably need a tune-up as well. And, I've usually got 5-6 on board with coolers, toys, and more. The bimimi deployed is a major speed suck. No catalyst in 2006. I'm sure my 5.0 carb adds some weight without added hp. It was kind of an odd engine choice, which with pollutions regs. is probably why it is gone now. But, when you search for a solid used boat, you make some compromises, and the 305 carb V-8 sounds nice and takes me back to my high school days.
 
The key word here is refrain from prolonged operation at WOT. You can run all day long until you run out of gas as long as you are within WOT specs for your motor. The drawback is the increase in wear and decreased engine life. My friend I call fast Matt knows no other settings other than idle or WOT. His 01 larson is still on the original motor a VP 5.0 GXi. At about 600 hours. I don't have daddy pay for my gas though so I can't afford that luxury.
Dave 205 said:
I don't know several things with certainty - but I likely have the same prop, and basically the same boat, yours has some interior updates that began in 2008. I know my 5.0 (305) is basically the same 305 small block that I ran in my mom's 1978 Caprice. I think the 4.3 is a two cylinder chopped 5.7 (350) that was dropped in a bunch of small trucks and some full size GM cars starting in the early 80's. At heart, these are old engines with new tech tacked on. I fried an Olds 307 at WOT in high school.

Enough history - my Mercruiser manual recommends that afer break-in: "Operation at 3/4 throttle setting or lower is recommended. Refrain from prolonged operation at WOT RPM."

Mine may be a little bit of a dog, but it starts and runs smoothly, and has a hole shot that works for me. I bought it barely used in the spring, and still haven't sorted out where the PO was at with it, he probably did nothing. So, maybe a tune-up will give me a surprise in the spring. You are right, it should break 50 according to this Boattest.com reveiw:

http://www.boattest.com/boats/boat_video.aspx?id=965

Load, and water conditions have a lot of impact on my boat. I almost always start with a full tank, I have a tube on board that weighs 50lbs. by itself - a lot of stuff accumulates on board. When I have a smooth lake to myself, the boat gets an extra 5 mph at any throttle setting over consistent wind or boat chop.

The 21' Select series boats in the era of my boat had options going over 300hp, I'm sure for a reason.
Click to expand...
 
CV-23 said:
I read an article somewhere when Mercury tested the 350/260hp 4bbl merCruiser package it was run wide open 24 hours a day for a week with only stops for fuel and drivers. The hotter the oil got the better it ran. I'm not sure the 4.3L or 7.4L were ever tested like that. The Chevy 350's just seem to last forever. I have a 5.7L and 7.4L and run them at 3800rpms for most long runs.....4600 is their WOT, Mike.
Click to expand...


This testing was done at 505 Marion Road Oshkosh, WI 54901. I remember standing on the Wisconsin street bridge watching those engines all lined up, multiple brands, stern drives, outboards, all wide open, all churning the water on the Fox River.

There were no drivers, no refueling, no boats and no breaks. Everything was mounted to land. The engines ran until they stopped running.

Jim Merten was one of the people who did the testing. He now owns the business we sometimes talk about here at CSR for online Mercury maintenance parts.
 
That is very interesting Presentation.....more details on the results would be awesome. It just seems the 350 small block always last longer that a 454 big block in a boat. It could be the additional load on the 454 caused by bigger boats. I've been told my standard 454/330hp will last over 1500hrs in my 270.....I just turned 800hrs this summer. I put on about 50hrs a summer, Mike.

Just found this....http://www.mertenmarine.com/servlet/the-template/mertenhistory/Page
 
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CV-23 said:
That is very interesting Presentation.....more details on the results would be awesome. It just seems the 350 small block always last longer that a 454 big block in a boat. It could be the additional load on the 454 caused by bigger boats. I've been told my standard 454/330hp will last over 1500hrs in my 270.....I just turned 800hrs this summer. I put on about 50hrs a summer, Mike.

Just found this....http://www.mertenmarine.com/servlet/the-template/mertenhistory/Page
Click to expand...



That’s him, the right most person wearing the team jacket. The sideburns are gone and he’s older now.

I do not know how the 5.7 liter (350) did vs the big block. I’m sure he would know.

Keep in mind this type of testing does not reveal failures due to corrosion and age. Years ago Mercury would put in writing that a well maintained engine with sterndrive will last 1,500 hours or more (or similar wording) however real world results showed much worse results.

The most typical reason for early engine failure is damage done by overheating. This often relates to the cooling system and / or corrosion. For example, a failure of an impeller can cause a engine to overheat.

He did tell me the most common reason for engine failure in their testing was a collapsed oil filter. This led to the development of the Mercury high performance oil filter. It has a metallic mesh tube inside the filter preventing the filter material from collapsing. This was enough for me to make the change. Just you have the numbers if your manual calls out MerCruiser GM Oil Filter 866340K01 at about $7/each consider Mercury MerCruiser GM High Performance Oil Filter 881126K01 at about $16/each.
 
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Dave 205 said:
Enough history - my Mercruiser manual recommends that afer break-in: "Operation at 3/4 throttle setting or lower is recommended. Refrain from prolonged operation at WOT RPM."
Click to expand...

Other than the "run it like you stole it" crowd, everyone I know takes this approach, including my (retired boat mech) neighbor. I run WOT only about once a season and my big issue is that the fuel consumption (measured by filling, running, and filling again) goes thru the roof when I approach WOT for any length of time.
 
I know my boat really sucks the fuel at 4000+ but it surprises me that Mercruiser really wants you to run at 75% or less which is around 3600 RPM. I don't do it everyday, but I love to run at 4000 or so on that early evening return to the ramp when it's just glassy out there. I like to do do a WOT speed test and then settle in a bit lower. The hum of an engine at full stride and the hiss of water on fiberglass. Ah yes, that's my bliss.
 
I like to run at 4000 or 3000 those seem to be the sweet spots.
 
On my boat - 3600 rpm's is needed to make it efficient on plane. I run around 3650 to 3700 most of the time on plane. Slow cruise is 1600 rpm's.
 
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