why keep rpm low when on muffs?

[imported_DANA1]

i have seen diff. opinions concerning the use of muffs on alpha one drives. i have a1997 mercruisr 5.7 carbed, with a 1990 alpha one closed cooling 1/2 system "block only" i think raw water comes from impeller on outdrive? then flows thrue heat exchanger then out exhaust? if i increase my rpm the temp guage reads lower then at idle, both on muffs and in water so isnt a higher rpm cooling better?

 

[Haut Medoc]

Re: why keep rpm low when on muffs?

Not quite sure what you are asking.......
As long as the engine temp stays at 160 or so it doesn't matter......
I suppose if you saw a short temp spike after a hard run & you backed down to idle, that would be normal.....
You may be referring to where a manual might say don't run over 1500 rpm's, because you may collapse the hose feeding the muffs from increased demand from the impeller.....
That depends on the quality of the hose.......

 

[imported_DANA1]

Re: why keep rpm low when on muffs?

that makes sense thanks

 

[Don S]

Re: why keep rpm low when on muffs?

The reason they want you to keep it slowed down is to keep from overheating. Many places have low volume and pressure on their water hoses along with lots of types of muffs on the market.. The engine can overheat if you try to run faster. So for safety sake, they want you to keep it slowed down.
I doubt you could suck a hose flat as the muffs don't seal around the intakes that well.

 

[DHPMARINE]

Re: why keep rpm low when on muffs?

I always thought it was also a warning not to over rev the motor w/out a load.You certainly wouldn't hold a car engine above 2000 rpms long in park or neutral.(well maybe THAT'S why the warning is there.Sort of like don't touch flywheel with motor running).

DHP

 

[Coors]

Re: why keep rpm low when on muffs?

hmmm, I have a well, 40 lbs of pressure, I can gun my thru hull and shoot water 20 feet. Am I hurting something?

 

[Don S]

Re: why keep rpm low when on muffs?

hmmm, I have a well, 40 lbs of pressure, I can gun my thru hull and shoot water 20 feet. Am I hurting something?

Not if it doesn't overheat or you over rev it.

Good Grief Guys...... It's "fine print", "Lawyer Speak", or otherwise a "Cover Your Azz" statement for when some fool puts it in gear and runs the engine at full throttle in his driveway to test WOT and the engine blows up at 12,000 rpm, Merc doesn't have to buy the engine.

 

[Boomyal]

Re: why keep rpm low when on muffs?

hmmm, I have a well, 40 lbs of pressure, I can gun my thru hull and shoot water 20 feet. Am I hurting something?

Naw, let er rip. Let your motor be the concern, not the coolant (water). Just do not do anything that you would not do with any unloaded motor.

 

[JUSTINTIME]

Re: why keep rpm low when on muffs?

u will collapse the hose, and might overheat

i have seen it!