Idleing Dry - Impeller Replaced!

[armysfcret]

How long can a 60 horse Merc idle after being pulled out of the water without damage?

 

[Spidybot]

Re: Idleing Dry - Impeller Replaced!

Some seconds.<br /><br />As soon as the impeller runs dry it's damaged. The impeller sits in the lower unit so as soon as the water pickup holes are not submerged, the problems start. <br />If you need to trim/tilt high at least make sure the pickup holes are under water (about the point then the prop becomes visible over the surface).<br /><br />You must supply water when starting the engine. If you use muffs you should stay below 'fast idle' rpm.

 

[andrewkafp]

Re: Idleing Dry - Impeller Replaced!

If you mean with NO water or muffs..<br />Don't do it.. It will damage your impeller and if you run it until it heats up, will damage pistons, cylinders and maybe even warp a few things. I would say 10 minutes from dead cold and 5-7 minutes if it's been run.<br />If you want to check for damage.. do a compression test.<br />Sorry UU Replied at same time

 

[Spidybot]

Re: Idleing Dry - Impeller Replaced!

Take care... it may take 10 mins. to heat the motor to the limit but the impeller will fry at once.<br /><br />G'day, Unicorn

 

[armysfcret]

Re: Idleing Dry - Impeller Replaced!

Just wondered. Pulled her out last December with my dad helping and realized she was "putt..putting" and turned her off. Maybe as much as five minutes. Hadn't even left the ramp yet. Haven't had a chance to start since then but want to get her ready for trip soon. I have muffs and will give it a shot. Impeller? Water pump impeller?

 

[outboardguy]

Re: Idleing Dry - Impeller Replaced!

Replace water pump impeller now!!! Do not run it.When you ran it dry the impeller blades vulcanize to the sides of the housing, so if you try and run it on a hose now all you will do is send chunks of impeller through the system with the garden hose pressure.Once that happens finding the pieces can mean total engine teardown.Hopefully you won't have any other damage after you replace the impeller. Good Luck

 

[roscoe]

Re: Idleing Dry - Impeller Replaced!

If it ran that long, you probably should change the entire water pump, not just the impeller.

 

[armysfcret]

Re: Idleing Dry - Impeller Replaced!

Great news. I have a 75 gallon water tank I used for testing engine before we take off to the lake. Doesn't everyone do a run up before they get to the ramp? Filled the tank, started the engine (no muffs as per outboardguys suggestion). Nice smooth stream of water out of "pee hole" and no rough running or anything. Does not appear there has been any damage to impeller, pump or engine. WHEW!!! Thanks for the feed back guys. Outboard: Glad you threw that piece in there about the muffs or I would have used them instead and with my luck there would have been impeller damage.

 

[LubeDude]

Re: Idleing Dry - Impeller Replaced!

It may not appear that there is, but there is!!! Change the pump like suggested! Youve received good advice, now take it. No impeller will last if run out of the water for 5 min.

 

[armysfcret]

Re: Idleing Dry - Impeller Replaced!

LubeDude,<br />Would the fact that the water pump was replaced within the last 25 hours of use help my situation. Was replace just before I bought boat last spring. I am a firm believer of "It it ain't broke, don't fix it." Like I said, nice stream of water and no apparent problem. When I referred to idle, I meant LOW idle. As I said, just kind of a putt....putt... and of course not in gear. Hardly could hear it running when I noticed the problem.

 

[Spidybot]

Re: Idleing Dry - Impeller Replaced!

You've missed one important point:<br /><br />By starting it at all, you've made water flush around inside the water jacket, bringing rubber fractions from the impeller all around. You were warned not to run it on hose, but a bucket has the same effect - the impeller flushes the system!<br /><br />A new impeller has a pretty tight fit in the pump housing so dry run is no better (rather worse, in fact) than a worn imp.<br /><br />LubeDude wrote:<br />

It may not appear that there is, but there is!!! Change the pump like suggested! Youve received good advice, now take it. No impeller will last if run out of the water for 5 min.

PS! The cost of replacement now will be a fraction of the cost you'll be facing once stuck out there with a seized motor. Add to this the inconvenience and embarrasment. And safety aspect.<br /><br />It's your motor, boat, money, life & safety on stake. Take the advice or the risc. Your call.

 

[quantumleap]

Re: Idleing Dry - Impeller Replaced!

Funny how people ask for advice but don't want to follow it if it's any inconvenience or costs them money. You guys tried, and couldn't have been more specific. Oh, well mybe next time!

 

[outboardguy]

Re: Idleing Dry - Impeller Replaced!

I didn't say don't run it on a hose, I said replace the impeller before you do ANYTHING !!!!!!! LIke I said the impeller blades were vulcanized to the side of the housing and you lighting the engine off has now torn them away from the sides of the housing, mostly in pieces.It probably has enough to cool at idle but at WOT thats a different story.It's your call but as you say "If it's not broke ,Why fix it"

 

[armysfcret]

Re: Idleing Dry - Impeller Replaced!

OK folks. Point well taken. I plan on having a spring tune up before we head out so will have the mechanic check pump also. I didn't want to give the impression that I was asking for advice and then not taking it. Guess it adds up to new-guy syndrome. I misread your post about using hose. It does say "don't run it". Guess I didn't WANT to hear the bad news. I have worked on classic cars for many years and I guess they are more forgiving. Being stuck beside the road with a minor break down is far easier to handle than stuck in the middle of the lake with seized motor I guess. <br /><br />Thanks for the feedback and the chastising too.

 

[LubeDude]

Re: Idleing Dry - Impeller Replaced!

The only thing that might have saved the impeller would be that you just pulled the boat out while it was running, but I still think that if it ran for five minutes like you said that I wouldnt trust it. Without a full flow of water, they get real hot, real fast. It will be interesting what your mechanic finds.

 

[jim phillips]

Re: Idleing Dry - Impeller Replaced!

I change mine every year $15.00 part 30 min. time <br />and no worries for the summer

 

[quantumleap]

Re: Idleing Dry - Impeller Replaced!

J&J: Nobody is trying to come down on you, but everyone here really knows their stuff and hates seeing someone make a mistake that can be easily avoided. To better understand the problem, imagine this scenerio: You have a high speed buffer, you take the bonnet off to expose the rubber pad. Now you take that buffer, turn it on high, and hold it on steady on one spot on a piece of plate steel for five minutes. What do you imagine happens to the rubber pad as it creates friction and heat? You can almost picture the pieces of molten rubber balling up and flying around. That's pretty much what happens to the impeller when run dry. Now, perhaps they made some significant advances in rubber construction over the past few years and they can withstand more heat, but I doubt it. Not for five minutes anyway. Listen to what the guys here have to say as I have learned more here over the past few months than in all of my last 15 years of boating combined! Good Luck, and I really hope that putting in a new impeller will take care of your problem.

 

[BJM]

Re: Idleing Dry - Impeller Replaced!

Hopefully my experience can put your mind at ease slightly. I inherited an old '66 Johnson 80 hp O/B and tuned it up, got it running, seemed to work well except it would overheat after 5 minutes on plane. I was new to outboards but knew never to run it dry. After opening it up the impeller was mangled with 1 of the 6 arms being 2/3 missing and the head of another was bonded onto its neighbour. The 4 good ones were pretty rough looking. The son of the former owner was a well known idiot and had probably run it that way in the past.<br /><br />So, all that to say that after swapping a new impeller in, the engine was fine. By the way the pee stream always looked fine on mine too. In your case you never revved it so the rubber probably got mushy and will probably come off the inside of the pump just fine. You definitely want to change that impeller regardless of the condition.

 

[armysfcret]

Re: Idleing Dry - Impeller Replaced!

Ok, as I stated before, I work on classic cars. Hudson Hornets to be exact. Have two show pieces in the garage. With that, I looked at the setup on the lower unit. I found the four bolts and the trim tab. Is it difficult to remove the four bolts and trim tab and just drop the lower unit to check the pump or is there much more involved and will I need any gaskets and such? What parts should I have on hand before I even drop the LU? I have the mechanical skills just don't have the knowledge of these water beasties.<br /><br />BTW - If anyone is interested here is the story on My Hornets

 

[quantumleap]

Re: Idleing Dry - Impeller Replaced!

Go to your nearest merc dealer, pick up a manual & a water pump rebuild kit. With your mechanical experience it's a piece of cake. Myabe an hour or two tops. Gotta have the manual though!