View Full Version : Brian Raymondís Impeller School

05-02-2005, 11:44 PM
Brian I see you lurking there!

Please tell me (us) about impellers. They appear to me to be a source of consternation and ripe for a design improvement. I used to be an engineer before I went over to the dark side.

What are they and what is their purpose?

What makes them unique on boats vs. cars?

I assume they are plastic, why arenít they made out of aluminum or other non-fragmentation material? If they are aluminum, can I get one made of titanium and never fuss with it?

What is the failure mode?

If you have a filter before the impeller, could the impeller then be redesigned to be more robust since it is less likely to come in contact with foreign material?

If you have a closed cooling system, do you need an impeller, do you need to replace it, if so, why is it not as robust as the water cooling system of an automobile? If it is as robust as an auto system, that would be one selling point for a closed system.

Next week gel coat - what is it - really :)


Brian Raymond
05-03-2005, 12:27 AM
Why aren't you in bed? A late night baseball game (my sons'), kept me from getting on sooner. The impeller itself is made of a nitrale rubber on a splined brass shaft, it is capable of pulling 600 gpm. This is the bad boy that draws water from the lake through the water intake to the circulation pump to keep the motor cool. Just like the alternator belt, it is a wearable item, and is not covered under warranty, it is compressed on one side to create the water draw. I suggest changing it evey 100 hrs. or at the beginning of every season. If the impeller does not seem worn, and still has stiffness in its blades, keep it in your glovebox for emergencies or other Indmar owners broke down that may need one. If a frequently cheked water strainer is not installed, make checking the in-side of the transmission cooler a part of your pre-launch for any foriegn debris. When on shallow, weedy lakes, make it a must. The impellars do not like air, and, being rubber, will disinegrate fast, hence, an overheated motor. The impeller works the same way on a closed cooling system, kinda. Instead of drawing water to the circulation pump, it delivers water to the heat exchanger to keep the antfreeze cooled, and then is discharged out of the exhaust. This has been a pretty novel concept, and has worked forever for motor manufacturers, that is why the material has not changed, and being a wearable item, it is not expensive to replace, and keeps the cost of motors down. The above preventative maintenance procedures will keep any boater a happy boater. The maintenance and replacement schedules are cheap insurance. Hope this helps. Keep us posted.

05-03-2005, 08:28 AM
Early in the day and late at night I can move the ball forward, the rest of the day is all defense.

I think the thing is rubber with a brass fitting so that when jammed it will fail rather than what is driving it. The concern there is foreign material lodging in the impeller. Rubber will also take an impact and return to its original shape. A solid part on a brass fitting would undoubtedly tear up the housing before it stopped spinning, causing more damage. Metal shavings and bits are also probably not desirable in the motor either.

It sounds like the design is optional water filter, impeller, engine water intake screen. I would guess that the screen is right at the engine, water hose connection. Iím not sure what the ďin-side of the transmit ion coolerĒ is or where to find it. Page 7-4 of the Indmar manual has a drawing but it is not clear to me which hose is the ďlowerĒ or rear hose.

I looked around in the Indmar manual. Chapter 8 is trouble shooting and it does not have a section on over heating.

Ya know, restaurants discovered that hosting cooking classes was actually good for business and made money. I bet a dealer course on boat winterization, basic care and trouble shooting could do the same thing. Food for thought (pun intended).


05-03-2005, 10:23 AM
Can the impellor be bought from you guys or a vendor.If a vendor do you know the part number for impellor and gasket.I own a 04 Mobius LSV carb. V drive.Thanks.

05-03-2005, 12:05 PM
Ed G,
Do you repack the shaft seal annually? I didn't know that needed to be done annually. If it doesn't need to be done annually, when does it need to be done and how do you know it needs to be replaced? What are the signs it needs to be replaced? Just got me thinking Ed. I have not replaced mine ever (2003 Model). Thanks.

james yarosz
05-03-2005, 08:42 PM
OK you guy's convinced me to change my 2 year old impeller.Now someone give me a part # and a place to order it over the net. Oh yea 2003 Outback LS 310 hp

05-04-2005, 06:17 AM
I know it's a Johnson impeller.......there should be a number on it........if you do a search on the web for Johnson and the number, you should find quite a few buying options......prolly in the neighborhood of 30-40 usd.

05-04-2005, 11:27 AM
JY, It's a Johnson 812. I buy mine at the local marine shop or from Discount Inboard Marine. About $30. Make sure you buy a gasket also.

Ed G, Thanks for the info. I'll take a look at the "drip rate" when it finally warms up enough around here to get her back on the water.

Brian Raymond
05-04-2005, 10:55 PM
The impellers and gaskets can also be purchased through your dealer or by contacting Indmar @; www.indmar.com. The impeller and gasket have been the same since 1986, but a eng. model would still be helpful when ordering. A rule of thumb on the shaft packing, it should be adjusted to 1 drop of water into the bilge every 30-45 seconds when the boat is in gear at idle. If there is no room on the shaft log for adj., it is time to replace the packing. You can get faxable or emailable (my word) instructions of this procedure by contacting; techservice@skierschoice.com. Brian Raymond

07-24-2006, 09:12 AM
I had some posts recently about my engine overheating. I replaced the impellar and the stuck thermostat. I took the boat out this weekend and the temp was screwed up again so I threw it on the trailer and took the freshwater pump apart. The new impellar was shot. When I say shot, it was missing all 12 rubber blades. I was able to recover 5 of them.

During the install, I used some vegetable oil (assuming it was non reactive with the rubber impellar) rather than a petroleum based lubricant on the inside of the ipmpellar chamber. I assumed this would work during initial startup to keep the impellar from overheating and provide suction. Upon review of the impellar, it appears the oil didnt affect the rubber, but rather all the vanes sheared off. on the outside of the housing opposite of the shaft.

Any install hints here to make sure this doesnt happen again? Also, any hints on how to get 7 vanes out of my engine? I was going to pull all hoses and use water and air to flush the block and headers until I could retrieve all the vanes.

07-24-2006, 09:18 AM
This sounds like NO water is getting in there at all, or something it sheering the fins off.