WOT, really?

[LazyCruiser]

Sorry, another newbie question.

So many times here I see WOT - wide open throttle, right?
Isn't that bad for your boats? It is in a car, right? Basically same motor, no?
I would just be afraid to have my motor going full blast, afraid that will ruin it,,,,,so I baby it. A Mercruiser 5.0 w/Alpha 1


sorry if this is a stupid question

 

[Scrawny]

Re: WOT, really?

With no load its devistating, but not a problem with a load. Ever floor your car up a hill?

 

[LazyCruiser]

Re: WOT, really?

With no load its devistating, but not a problem with a load. Ever floor your car up a hill?

Well yes but that's only for a short time. WOT across 5-10 miles of water takes quite a bit longer.

Anyways, thanks ;-)

 

[steelespike]

Re: WOT, really?

I do agree that wot with an automotive based motor is hard on them but
the red line on a marine motor is lower than that in a car. I wouldn't run wot
routinely with a automotive based marine motor in my mind the life of a motor run routinely at wot is shorter than that of one run at say 4,000.

 

[Vanover]

Re: WOT, really?

I agree. I run my outboard at WOT for hours. NO issues. They are designed for this. That is why they have inspection and mx interavals that are more strineant than a car/truck.

(sorry no sp check)

 

[45Auto]

Re: WOT, really?

Mercruiser recommends operating at 3/4 throttle or lower to prolong valve life. Up to you to define what "prolonged" means, and whether or not to follow the manufacturer's recommendations.

To increase valve life on all MerCruiser engines, the following recommendations should be considered:

Use a propeller that allows engine to operate at or near the top of its maximum RPM range when at full throttle with a normal boat load.

Operation at 3/4 throttle setting or lower is recommended. Refrain from prolonged operation at maximum (full throttle) RPM.

 

[drivehard]

Re: WOT, really?

I ran my 1995 5.0L Mercruiser at full throttle for an hour at a time several times. When I rebuilt my engine (cracked block) the internals looked perfect. The valves looked fine except for some carbon build-up.

 

[Texas Parrothead]

Re: WOT, really?

How do you determine what the top of your engines max RPM range is when at full throttle?

 

[drivehard]

Re: WOT, really?

How do you determine what the top of your engines max RPM range is when at full throttle?

It should be right on the top of the plastic piece that covers the flame arrestor on your Mercury. Guessing it is 4400 - 4800 RPM from memory...but it could be 4600 - 5000...can't remember for sure.

Edit: Yup, for your engine it should be 4400 - 4800 RPM

 

[QC]

Re: WOT, really?

One thing I like to mention in these threads is that you pay for horsepower. The engine makes it's rated power typically somewhere in the middle of the WOT range, so the only way to get what you pay for is to run it up there. There is no warning that says "if you buy horsepower from us we don't expect you to use it". The point being is they are designed to put out max power. Is that "good" for it? Like most things, it certainly isn't bad if used/abused moderately . . .

 

[Silvertip]

Re: WOT, really?

You don't WOT a car because a car has a transmission that will downshift depending on load and it is easy to spin it up to 6000 rpm or higher depending on the car and engine. On the flip side, if you could keep the transmission in overdrive without downshifting at WOT the car would likely blow up as well as it would overheat. Boats don't have transmissions so they need to get you out of the hole, cruise and reach top speed with one gear so it is essential that you prop for WOT.

 

[Brewman61]

Re: WOT, really?

WOT isn't so much bad for your motor as it's bad for your wallet!!

 

[45Auto]

Re: WOT, really?

I ran my 1995 5.0L Mercruiser at full throttle for an hour at a time several times. When I rebuilt my engine (cracked block) the internals looked perfect. The valves looked fine except for some carbon build-up.

You must have much better eyes than most people. No one I know can see 2 thousandths (.002) of an inch out of roundness in a cylinder, or 2 thousandths of an inch in taper in a cylinder bore. That's the service limit on a 1997 5.0L cylinder bore (a human hair is about 3 thousandths (.003) of an inch in diameter).

 

[115johnson78]

Re: WOT, really?

I would say you should run the engine as you feel

My 2 brothers run them under the recomended manu's rmp's.(both I/O)

But I try to run myine close to the recomended cause too much bogg(bogg +
overworked= $$$$$) can be just as bad as too much rpm's.

 

[QC]

Re: WOT, really?

Recommended WOT range is NOT for selecting a cruise RPM, it is for selecting the correct propeller . . . After you get the right propeller from finding the right WOT RPM, then cruise wherever you want to.

 

[walleyehed]

Re: WOT, really?

Recommended WOT range is NOT for selecting a cruise RPM, it is for selecting the correct propeller . . . After you get the right propeller from finding the right WOT RPM, then cruise wherever you want to.

For the love of God, Thankyou QC for putting into words what I was thinking....
As mentioned above..you set the entire spectrum by selecting the prop that allows max recommended at wot....everything else falls into place.