Running a water pump dry

[Vic.S]

What would be the longest time it would be safe to run a small engine with the pump dry. An 4hp merc for the sake of the argument,

Not at all

A few seconds to just fire up and shut down again

For half a minute

Longer than that. Suggest a rtime

 

[jbjennings]

Re: Running a water pump dry

No Doubt on this one! Not at all.
Mercs are already finicky on the cooling system. You don't want to mess it up--trust me!
Get yourself a trash can and test it out.
You may get away with 15 or 20 seconds, but you might not. Especially if the impeller is dry from sitting/brittle.
If it hasn't been run in a while, you can just about bank on ruining the impeller by running it dry. And when you put it in water and crank it, little pieces of impeller blades will go into your water jackets and you're really in a bind. I saw a guy last weekend start his '76 merc up out of water for about 6 or 7 seconds, and he made it back just fine. I sure wouldn't do it on purpose, though.
JBJ

 

[kennyboater]

Re: Running a water pump dry

not at all

 

[AguaSki]

Re: Running a water pump dry

Everyone always said to never run with out water and so I blindly obeyed, but I did not understand why until I rebuilt my first water pump. After you do a rebuild you can see how the water pump works, and you won't want want to run it without water. I will even say don't crank your starter without water. Even if your doing something, and you don't plan for the motor to fire up. When you are cranking, the impeller is moving, and it should not move without water.

 

[jay_merrill]

Re: Running a water pump dry

I've done it before with no ill effects but I don't recommend it. I also don't do it any more, because it really doesn't make any sense to do so. If you are going to start your motor, take the time to insure proper cooling of the entire motor - including the water pump.

 

[Vic.S]

Re: Running a water pump dry

Thanks for the comments. It is not something I have done or would do but I asked because a statement I made on another forum to the effect that running dry " even for a few seconds" could damage the impeller was challenged!

 

[TOHATSU GURU]

Re: Running a water pump dry

It's considered routine to dry start outboards to see if they will start. I don't see anything wrong with that as the engine would be running dry for less than 2 or 3 seconds....If it starts. You?re not going to hurt the engine itself until the engine surpasses its operating heat range and that would take minutes. But, you do run the risk of accelerating wear on or destroying an impeller after X amount of seconds. So I would say that while you can dry start, you shouldn't make a practice of it.

 

[dimock44]

Re: Running a water pump dry

NEVER run dry!! I can fill a garbage can or put the muffs on about 1000 times faster than I can drive to the boat shop and blow 15-30 bucks on and impeller and then pull the lower end and change it. Along those lines I have resurrected several dead and stored motors. I always let the motor sit over night in a barrel of water before starting them. Reason being something I was told about weed eater line. I bought a 500 foot roll one time and it was brittle and broke way to often. When I asked about returning it the lawn mower guy said I could return it or try soaking it in a pail of water for a couple of days. I soaked and am still using it 7 years later. Thought it might work on dried out impellers. So far I have not needed to replace the impellers until I was sure the old motors were worth keeping.

 

[ztim]

Re: Running a water pump dry

When I was about 22 years old and had my first boat and motor, I used to start it just before putting in. Usually when it was real cold outside. I did that for years never being taught it was a no-no. Now that I know better, i would not do it anymore.

 

[NSBCraig]

Re: Running a water pump dry

man it's not a matter of hurting the engine, it's the rubber impeller will not take it.

Don't even turn your motor over at all with out putting it in water.

Muffs work but why not just use a can or blue barrel?

 

[Benny1963]

Re: Running a water pump dry

my 150 ran about two minutes after clogging. new brp pump
oyster shell and petroleum mudd in pump

 

[AguaSki]

Re: Running a water pump dry

Yesterday I watched a group of guys run their motor for several minutes after retrieving at the ramp. They were having some trim problems, and for some reason they thought the running motor would assist with the trim issues. I was about to say something to the clueless group, but then I noticed someone else mentioning it to them, and they just blew the advice off. It was a good 5 minutes before they turned off the motor. About 2 minutes after the motor stopped I heard it fire up again for another few minutes. I eventually left the ramp area so I don't know how it ended, but I bet there will soon be a boat on Craigslist that only needs a water pump. It is a amazing that the motor did not overheat on the trailer, but the impeller has to be totally trashed as long as it ran without water.