Outboard WOT on flushing attachment

[mutiny]

So, there has been some conversation around the shop about the safety of an outboard engine running 5000 RPM in gear, on a flushing attachment. One of the new guys say that its perfectly fine. My head technician cringes and says its not only dangerous for everyone around the engine, but can do major damage to the engine itself. The new guy said to show him where in a service manual it says that it cant be run WOT in gear on the flushing attachment.

​I bring it to the forum for some friendly debate and discussion. The question at hand is..

CAN AN OUTBOARD MOTOR BE RAN WOT IN GEAR ON A FLUSHING ATTACHMENT? What damages can happen if any and why? Is this a good way to test your outboard?

 

[ondarvr]

While it doesn't happen all the time, the motor can get into a runaway situation and you can't shut it off, the key or kill switch does nothing, it just continues to increase in RPMs until it blows up, or runs out fuel (I'm assuming after frantically trying a couple things you finally pull the fuel line off).

 

[roscoe]

(I'm assuming after frantically trying a couple things you finally pull the fuel line off).

Yes, if you have guts enough to get next to the motor.

An engine that normally runs at 5500 rpm, will rev much higher than that with no pressure on the prop.
Can you see your motor turning 7,000 or 8,000 or more rpm, before something seizes and shatters?

 

[flyingscott]

It's a bad idea and the muffs themselves used to come with a label on them and may still that 3500 rpm was the max.

 

[jimmbo]

The only time an Engine is run WOT in a shop is in the tank with a test wheel, or attached to the Dyno. One guy stuck a large engine in the tank hooked to the dyno, with a set of muffs with the water turned on. The water pump was able to collapse the hose feeding the water when it was at WOT.

 

[Scott Danforth]

looking at it from purely the cooling water supply:

the muffs provide a fixed amount of water at about 15gpm water flow rate.
the raw water pump is a curve dependent on engine RPM. at a bit over 1500 RPM, the raw water pump is now trying to draw more water than the hose can provide.

this would be bad because you are now starving the motor of cooling water.

looking at it from an engine RPM and loading point:

in a test tank or on the water (or even a dyno), the engine is loaded and working against that load to where it will be limited to 5000-6000 RPM
on the muffs, there is no load, and the engine may run away. when this happens, the speed gets to the point where piston speed is beyond the capability of the lubrication to help, the bearing speed is beyond the capability of the lubrication to maintain a film and the motor will easily see daylight from the inside as the pistons decide they want to come out and fly across the room.

this is not limited to outboards or two-strokes either.

this can be fatal to any bystanders because when parts grenade from a run-away motor the shrapnel usually takes out what ever is near the motor. There is a reason dyno rooms are two courses of sand-filled block with metal plate in between.

PS, if the new guy was told not to, and he remains defiant and belligerent and ran a motor to full song on muffs, he would be the new unemployed guy

 

[GA_Boater]

Tell the guy who thinks it's OK to run WOT on muffs to start his car or truck and hold the the gas pedal to the floor in neutral. I bet he says that can hurt his car. Running on muffs is the same thing - No load. Actually worse because a vehicle doesn't need outside water for coolant.

If I caught a shop running WOT on muffs on my motor, the shop would never see one more dime from me and their ears would be blistered.

Is this guy a trained, certified tech?

 

[mutiny]

These are all very good points and I agree with them all. I have always been told to never exceed 2500 rpm's in gear out of the lake. Of course our shop has a dynamometer so I think this was more of a just shop debate than anything. I've already laid the ground rules and for bid anyone to ever run any engine without restraint.

I also used the car theory. Explaining to put your car on jackstands, put it in gear, and then Peg the Excelerator. Not only does it sound wrong while it's running but definitely could achieve a runaway catastrophic over speed.

Thanks for all the viewpoints and opinions. My thoughts remain that it's a terrible idea and won't be tolerated in my shop.

 

[Mohawkmtrs]

The manual also does not say "Do not sniff the fumes from the fuel tank" or "Don't smoke near gasoline"...does he think it's OK to do either?

 

[mutiny]

The manual also does not say "Do not sniff the fumes from the fuel tank" or "Don't smoke near gasoline"...does he think it's OK to do either?

LMAO!! This is fantastic. Now I'm looking more forward to Monday

 

[Grub54891]

Wow! Some will not listen to anyone. We had a tech when believed in his impact gun much to often, he is no longer with the marina......

 

[jimmbo]

Wow! Some will not listen to anyone. We had a tech when believed in his impact gun much to often, he is no longer with the marina......

There was an "impact kid" at one of the local dealerships 35 yrs ago that assembled engines being overhaul with an impact wrench.

 

[robert graham]

5000 RPM's on the muffs!....What ever happened to just common sense!.....

 

[Sea Rider]

I find much better for OB to run on muffs while geared specially when decarbonizer products are sprayed through carbs than at idle as those products must be sprayed between 2 to 2.5 K revs. Just be aware there's a spinning prop at high revs, people should not come close to rear of OB. Is it possible to run a test prop while on muffs at higher rpm or it's intended for water tank testing only ?

Happy Boating

 

[Chigwalla]

I find much better for OB to run on muffs while geared specially when decarbonizer products are sprayed through carbs than at idle as those products must be sprayed between 2 to 2.5 K revs."

Just like a power check, you can do that with the boat tied to the dock.
That way, there's a load on the prop, though you do have to watch for the prop venting because the ambient water isn't moving with respect to the torpedo.

 

[Sea Rider]

Being decarbonizing OB's for years while on muffs and geared, runs much even under load that at idle which has shaking issues when trottle is backed. Just need a opt water flow from hose and that's it. If tied to a pier OB will need to be geared forward to achieve same effect as on muffs.

Happy Boating

 

[Daveamd]

Well, just for my 2 cents worth, the Seloc manual online DOES state that you "must not run any engine at WOT on water muffs, as engine runaway can occur", so I believe the manual does indeed state that you cannot run WOT on muffs!
Aside from that, not all chainsaw manuals state "Do not attempt to stop chain with limbs or genitals" (my husqvarna does!), but pure common sense should dictate you just don't do it! (So don't!)

 

[jsparks747]

I just let it idle or switch it into gear but not at anything more let alone WOT.