Running boat on land with no prop?

[racerone]

Water should be well above the impeller , like 6 or 8 "

 

[muc]

Water should be well above the impeller , like 6 or 8 "

So with a OMC Cobra drive in a 18’ runabout. The swim platform needs to under the water to run the engine?

Again I’ll ask ——- where are you people getting this information from?

 

[racerone]

Nope-----Once the pump is primed and the boat is moving it is a different story altogether.------And I have worked on many different machines and pumps.------Pumps with 3000 HP and also 12,000 HP motors driving them.

 

[poconojoe]

I'm no expert by far, but it would seem that real world conditions, aka boat in water, should trump simulated (on land) conditions.

Why don't you just put the boat in the water to see if it's operating properly while under a true real world load?

I don't mean to be derogatory, just wondering.

 

[Rick Stephens]

Don't know about Mercruiser stating anything, they only mention muffs in their user manuals (I looked), nothing in service manuals and they deleted sterndrive flushing video off their website. I smoked my first impeller running things in a water trough. Maybe should change to an oil thread to all come to agreement.

 

[Buster53]

Ok, why is the OP running his engine 30 minutes or more? If he’s just flushing, sounds like major overkill to me.

 

[ROY WILLIAMS]

the muff is correct ... the water tank is a bit lower, the impeller ...then the impeller is wearing out ...hot ..

 

[newtoboat101]

brand new 5.7 motor vortec ,pulled 5.0 out, just got it running still in break in period and want to fine tune motor with load ,not ready for wot yet ,but was wanting to do all this on land ,thats why the tub ,for resistance for tuning ,if that makes sense ,no where close to run in lake or river,do not live close to water source , looking at putting back in next april,

 

[Buster53]

brand new 5.7 motor vortec ,pulled 5.0 out, just got it running still in break in period and want to fine tune motor with load ,not ready for wot yet ,but was wanting to do all this on land ,thats why the tub ,for resistance for tuning ,if that makes sense ,no where close to run in lake or river,do not live close to water source , looking at putting back in next april,

I’m no expert, but I’m guessing you really need to get it on the water to properly break it in. Even if it is an hour or two away…make the effort.

 

[WIMUSKY]

I’m no expert, but I’m guessing you really need to get it on the water to properly break it in. Even if it is an hour or two away…make the effort.

No doubt about it. ..

 

[Bondo]

brand new 5.7 motor vortec ,pulled 5.0 out, just got it running still in break in period and want to fine tune motor with load ,not ready for wot yet ,but was wanting to do all this on land ,thats why the tub ,for resistance for tuning ,if that makes sense ,no where close to run in lake or river,do not live close to water source , looking at putting back in next april,

Ayuh,..... That's not feasible, as the prop will empty the tub quicker than you can refill it,....
Not near load enough for a break-in either,....

 

[Scott Danforth]

if you want to break it in on land, install it in a truck or pay for dyno time.

otherwise follow the factory manual for breakin

 

[muc]

Nope-----Once the pump is primed and the boat is moving it is a different story altogether.------And I have worked on many different machines and pumps.------Pumps with 3000 HP and also 12,000 HP motors driving them.

So with that Cobra I mentioned, you only need the swim platform under water when it's first started?

I've worked on a lot of stuff, but I gotta ask. What has 12,000 HP that drives a rubber vane water pump?

 

[racerone]

Pumps behave according to rules and physics,-----They do not work the way some folks think they do.

 

[muc]

Pumps behave according to rules and physics,-----They do not work the way some folks think they do.

Could you explain how the rules and physics apply to your statement --- "Water should be well above the impeller , like 6" or 8" ---- I'm not sure if the folks at Johnson pumps know about this. Here's a cut and paste from their marine pumps catalog.

The primary advantage of a flexible impeller pump is its self-priming ability. As the vanes of the impeller are depressed and rebound, they create their own vacuum drawing fluid into the pump. A dry pump can lift water up to as much as 3 meters. Thus a flexible impeller pump being used for engine cooling needs not be located below the water line or manually primed.

Here's a cut and paste from Jabsco pumps --- one of the other big players in marine engine cooling flexible vane pumps.

Engine cooling pump​

Flow rate: Nominal 53 Litres/min (14 US gallons/min) at 1500rpm
Self-priming from dry up to 2.4m (7.8ft)

I'm still waiting for someone to post where they are getting this false information from. I'll admit when I'm wrong about something, but in this case everything I've observed and the two main manufacturers of flexible vane marine engine cooling pumps seems to say I'm not wrong.


So to all the posters who think these pumps need to be submerged anywhere from 1" to 11" ----- prove me wrong --- I dare you, heck I'll even go straight to the triple dog dare! Come-on tell me how you know I'm wrong, is it a "gut" feeling?

 

[dubs283]

Trust me muc, once these guys have their minds made up no amount of factual information is going to sway them.

I'm with you on this one, I have much experience in the field and can confirm all the facts you are posting. The problem with this forum is when one is pragmatic it increases the disinformation from others.....

 

[Scott Danforth]

@muc, I will put $100 that says if you run that impeller dry, and try to draw water 2.4 meters, you will turn the impeller to a burnt little crisp long before water ever gets to it. look at my profile on linked in and look to see whom I am connected to at VolvoPenta/Merc/PCM/Cummins/John Deere/Cat/etc.

I can only go by what the lab testing results were and how they were communicated back to us

Brunswick even posts a few pages in their manuals on what happens to the impeller after 45 seconds of not being submerged when operating.

 

[Lou C]

Well I’ve never run my Cobra in a trough but when I launch it the ramp is shallow and the top of the outdrive is just barely submerged (impeller housing in these is in the upper gear unit); it always primed I never had a problem with it running hot when launching. I do run it on the muffs at home before launching though. About the muffs; I have had problems with those dual inlet Tempo style muffs because the rubber is too stiff to conform to the shape of the lower unit. The round Merc/Quicksilver ones with the clamp work best; the rubber is softer & more flexible.

 

[newtoboat101]

(LOU C :The round Merc/Quicksilver ones with the clamp work best; the rubber is softer & more flexible.) i will look into these ,mine dont form well and leak water out

 

[newtoboat101]

back to original question ,is it ok to run boat (with muffs) with no prop on