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Author Topic:   Did I Fry The Impeller?
minimontauk posted 10-13-2003 10:27 PM ET (US)   Profile for minimontauk   Send Email to minimontauk  
Pulled a major stupid today. I was flushing the engine with a hose and ears. Ran it with the hose on at low nuetral idle for about 5 minutes to warm it up. I shut the hose and motor off to attach my can of fogging oil to the port on the automatic choke, like a bicycle tire air nozzle. I restarted the motor for about 45 seconds while squirting in the fogging oil in two 2 second and one 20 second burst until the engine conked out, per the directions. You guessed it, didn't turn the hose back on. I assume that the impeller is toast, but I hope I didn't fry anything else. I can't imagine any engine heat damage in that time, espescially as it was gagging on fogging oil. After much self abuse, I could use some friendly advice. Anything more serious than a water pump rebuild in my near future?
minimontauk posted 10-13-2003 10:29 PM ET (US)     Profile for minimontauk  Send Email to minimontauk     
The impeller is the three-bladed hard rubber type, not a metal one. The engine is a 97' Johnson 48 HP, no VRO.
Sal DiMercurio posted 10-13-2003 10:59 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I'm sure you didn't damage the engine but you did hurt the impellor big time.
Change it even if it still pumps because you softened the blades & they will no longer push or pull water as they should.
Do not put the engine on the hose to see if it's pumping because even without a water pump the hose preasure will push water through the system give the illusion that all is well when it isn't.
ShrimpBurrito posted 10-14-2003 01:07 AM ET (US)     Profile for ShrimpBurrito  Send Email to ShrimpBurrito     
And when you install the new impeller, it's a good idea to put a light coating of grease (vaseline, triple-guard, etc.) on the impeller housing. Someone at a shop I was at supposedly neglected to do that and the impeller fried and the engine overheated. I'm sure that doesn't happen all the time, but it's not worth the risk.
minimontauk posted 10-14-2003 08:39 AM ET (US)     Profile for minimontauk  Send Email to minimontauk     
Thanks, now I can start breathing again. I have a shop manual that describes a "water pump repair kit", complete with impeller, housing, gaskets, etc. I'm gonna get one and replace it all. I bought the engine used, so I have no idea how old the one in place was anyway, probably all for the best.
jimh posted 10-14-2003 09:00 AM ET (US)     Profile for jimh  Send Email to jimh     
Rather than grease, I have seen a recommendation to use liquid dish soap to lubricate the impeller when installing it. This seems like a reasonable idea, as the soap will soon be washed away by the water. A coating of grease might hang around for a while.
Tom2697 posted 10-14-2003 04:19 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
Any petroleum based product could harm the impeller depending upon the material. I would recommend the dish soap as jimh suggested or use a light coating of vegetable oil. I have to mention though, any oil-type product will be frowned upon by the tree huggers around you when you relaunch your boat. Even a "friendly oil" like corn oil will leave a slick on the water...
ShrimpBurrito posted 10-14-2003 11:51 PM ET (US)     Profile for ShrimpBurrito  Send Email to ShrimpBurrito     
But don't you think a petroleum based product would be washed away within a few hours of usage? You'd think that after a number of hours with the impeller exerting a fair amount of pressure against the housing while spinning water through it would wash it out.

BTW, I just checked my OMC service manual, and it says to coat the housing with "oil".

JoeH posted 10-15-2003 01:09 AM ET (US)     Profile for JoeH  Send Email to JoeH     
Would the damage really be that severe after 45 seconds? Sometimes it seems to take forever to see the stream on the first start after the motor has sat. His had been running just minutes before so it couldn't be completely dry, like on initial start-up. And if the impeller is that sensitive how do you handle start-up? Joe
Perry posted 10-15-2003 03:13 AM ET (US)     Profile for Perry  Send Email to Perry     
In his initial post, he says 45 seconds followed by a another 20 seconds. Over a minute without water would have me replacing the impellor if it was my motor.
bsmotril posted 10-15-2003 10:33 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Even though it takes a minute for the telltale stream to appear, the impeller has normally been submerged in water from the get go. It just takes a while for the pump to fill the water passages in the block and then exit the telltale, the last part of the the cooling system typically. So even though it takes a while to get water out of the telltale, the impeller is still wet right from startup. Start the motor without a water supply and the impeller runs dry immediately, you get friction and then heat in short order which destroys the impeller vanes. Take a piece of rubber like a squeegee end and rub it across a smooth piece of metal as fast as you can. Now multiply that speed by about 5-10X and you've got something analagous to a dry impeller. Now try it under running water and see the difference.
minimontauk posted 10-15-2003 01:12 PM ET (US)     Profile for minimontauk  Send Email to minimontauk     
Well, I didn't have a stopwatch on, but I know it was less than a minute running dry. My OMC shop manual says 5 seconds dry is enough to fry it, so I am definitely replacing the impeller. The shop manual says to coat the impeller cup inside with "light oil". I was picturing good old 3-in-one. I have observed the removal of the lower end once (me standing there watching my gearhead brother in law). So I have a basic grasp on the process. I remember you have to unbolt the starter to get access to the top of the shifter rod. The shop manual gives a reasonably clear description of the whole process, but I am a little paranoid about screwing it up. Is there any way to test the whole assembly without starting it up, like rotating the flywheel by hand, or cranking without sparkplugs? Would that generate a telltale water stream?
Tom2697 posted 10-15-2003 02:19 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
Petrolium-based products will begin to degrade most rubber materials immediately. While the effect may not be immediately apparent, the overall life of the impeller would be shortened. Chances are, the impeller will fail at the worst possible moment....aka "Murphy's Law"

The manual states to "coat the housing", not the impeller. Of course, some manufacturers use different materials for their impellers. A salesman (hence why I didn't believe him) told me that one motor (don't remember which brand) can be run at idle for up to 3 minutes without water and without damage. I'd rather not risk it since Joy costs $0.97, Canola costs $1.96 and a new motor costs quite a bit more.

brisboats posted 10-16-2003 09:50 PM ET (US)     Profile for brisboats  Send Email to brisboats     
The dish soap on the impeller works great and makes the installation into the impeller housing easier. I cannot remember the manufacturer but we use to use tubs of a pink soap that applied like vasoline at the marina. The beauty was you could coat the impeller and this stuff would still be there after a long layup. Something you just would not want to do with a petroleum based product.


Gene in NC posted 10-18-2003 05:19 AM ET (US)     Profile for Gene in NC  Send Email to Gene in NC     
I doubt that you hurt the impeller. My experience is slipping of the rubber on the metal sleeve or hub, not damage to the vanes. Even if the hub starts to slip it seems to get so hot that on cool down it will vulcanize itself back to the sleeve. Ask me how I know?

On '66 OMC 100 plug wires were crossed so bad that engine ran backward for a bit and even that didn't damage the impeller.

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