Strange Cooling/impeller Problem - 1996 Johnson 3hp

I bought this tiny little twin (1996 Johnson 3hp, mod J3REDS) just yesterday and already ordered a new impeller and factory repair manual from my dealer here. Experience has tought me that both are worth the $$ for a used outboard. Cranked it up just now to watch it run for a bit and make sure everything is OK for the lake tomorrow and something wierd happened. It peed water just fine at idle but when I engaged forward gear and rev'd it up it quit expelling water! When I idled it back down the water started peeing out again with a little steam. I shut her down instantly, waited for to cool down and tried again. It's definitly repeatable. There is no burnt paint on the head at all and no other signs of maltreatment. Is this simply a bad impeller? In my experience impellers work or they don't, but I generally rebuild 60's era outboards. Any insights welcome!

Re: Strange Cooling/impeller Problem - 1996 Johnson 3hp

if it was in a barrel, putting it in gear took the water away from the pick up. try it tomorrow, in the water, just watch it, hopefully you did not burn up the impeller.

Re: Strange Cooling/impeller Problem - 1996 Johnson 3hp

Cool, thanks for the reply. It only ran about 5 seconds with no water, for 3 times total. None of my others have done that so it took me by surprise. Will try on the lake and update this post tomorrow.
One question - How long do impellers generally last? I replace them first thing on a new-to-me outboard but have never kept the same one for more than a year or two.

Re: Strange Cooling/impeller Problem - 1996 Johnson 3hp

How long do they last? Depends of a couple of factors. If they are not abused by running dry, or in very muddy or sandy water, certainly two years. I've seen motors that haven't had the impeller changed for 8-10 years , and they pump water but they all reach a point of diminishing returns. The worst case scenario is the impeller flys apart and washes an arm fragment up into the water tube or power head and blocks the cooling passages. The impeller arms are constantly under tension in the impeller cup and will take a set and loose flexibility over time. Ability to pump water at both low and high speed operation will be greatly impacted with an old impeller. I consider the water pump a normal maintenance item and really cheap insurance. It's my experience that the pump doesn't work one day and not the next...it a gradual thing until the pump can't push enough water to cool the power head. The only exception is, as I mentioned , an arm blocking the water tube or water passages. Most here will say to replace the impeller on a 'new to you' motor and is good advice, even when the seller assures you that 'it was recently replaced'....but that's just me, I trust my own work. I do keep a journal of maintenance records on my motors to be sure of what was done and when.

Good advice from TD, run in lake and watch it closely until you can replace the impeller and know for sure it's cooling well.

Re: Strange Cooling/impeller Problem - 1996 Johnson 3hp

Indeed, it pumped just fine on the lake. Never had one do that before in the barrel so it took me by surprise. New impeller will be here next week and I'll get a new one in there anyway. Strange design on this thing though, it doesn't have reverse but will spin around 360 deg. However, when I do that it pumps water into the boat. Just a minor irritation, otherwise it's great. A remarkably powerful little thing!