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Old 22-04-2011, 08:20   #1
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OMC Zephyr Saildrive

Hi,

I'm new here and I hope I'm in the right forum.
I have a 1981 Aloha 8.2 with a 15HP OMC sail-drive which works awesome. I've been using it moderately for five years and noticed some loss in coolant water flow last season. Replacing the impeller involves basically removing the engine and I'd rather not if I didn't have to.

My questions is, can I somehow add an electric water pump into the cooling loop and just forget about the mechanical one? This motor picks water up from the lower end just ahead of the prop and discharges through a wet exhaust riser/water-muffler set up.
There is a drain cock on the front of the engine and I was thinking I could make a fitting to enter the loop there and bring supply in through a new raw water strainer. Would the forced water supply simply find it's way to the exhaust?

Could this work?
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Old 22-04-2011, 08:24   #2
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Re: OMC Zephyr Saildrive

The water flow from the pump increases or decreases dependent on engine rpm. A single speed electric pump won't do that.
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Old 22-04-2011, 08:31   #3
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Re: OMC Zephyr Saildrive

Greetings and welcome aboard the CF, _floater_.

Check out the
SAIL DRIVE DOCUMENTATION pages
Here ➥ documents
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Old 22-04-2011, 08:43   #4
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Re: OMC Zephyr Saildrive

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The water flow from the pump increases or decreases dependent on engine rpm. A single speed electric pump won't do that.
I thought about that. Does it matter?
As long as it keeps up with highest demand...could it possibly be kept too cool?
Hell I'd even consider a thermostat relay. Anything to avoid removing the engine and messing with near-impossible to find seals and gaskets.
Maybe it does matter
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Old 22-04-2011, 08:50   #5
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Re: OMC Zephyr Saildrive

I suppose you could rig some kind of variable speed motor that runs in lock step with engine rpm but that gets complicated and could be costly. You would need to know pump out put at wot rpm and size the pump accordingly.
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Old 29-08-2012, 12:29   #6
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Re: OMC Zephyr Saildrive

Floater, I am now faced with this same situation and really not looking forward to getting into this saildrive to replace a little rubber impeller. What did you finally end up doing? I love the idea of an external water pump for many reasons.
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Old 26-09-2012, 13:10   #7
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Re: OMC Zephyr Saildrive

Sorry for the late reply, I haven't been on here in a long time.

I ended up changing the impeller which was quite the ordeal. The experience did allow me to fix a few things at the same time though.

The impeller replacement did involve removing the entire engine for me, including the bottom end, because the ISO ring had been improperly installed the last time the motor was out and was pinched so badly out of position on one side that the aluminum casting was wearing away at the fiberglass. So repairing that was a hidden blessing and only possible because I has a spare ring that I got with a reconditioned motor I have as a spare.

The impeller needed several trips to the dealer before I got the right one, but they had it in stock. Someone told me later that there are blue silicone replacements available that have a greatly extended life. I was unable to find one.

I had the chance to repaint everything and reseal everything at the same time so that was a good thing too.

I think I burned the impeller out by testing the engine out of the water in the spring. I set up a tub and submerged the entire lower end in water before starting. I thought it would just draw it up and spit it out. I even saw water squirt out the exhaust. But if you watch for just a few seconds longer than I did, you'll find that was old water trapped in the exhaust/hoses that I saw spit out and the engine was now running dry because the impeller WILL NOT DRAW WATER UP THE LEG INTO THE ENGINE. The actual engine must be below the waterline for it to draw water UNLESS you pressurize the source and force water up to the impeller. I didn't know this and that was the reason for needing one in the first place. Huge mistake. Stupid.

As for the future, I will do an automotive water-pump if I ever need to replace the impeller again. A friend tells me speed doesn't really matter and it changes with RMP only because it's driven by the motor itself. He says temperature is more important and that the thermostat could be used to trigger a relay to the pump, turning it on and off as required to maintain the right temp. (something like that..I forget exactly, but he said it would be simple).

One last thing...I still love this motor.
Super dependable. Low maintenance. Lots of power and always fires right up even without choke. Except for the stink of 2-stroke oil...you couldn't ask for a better auxiliary.

http://www.youtube.com/user/27floater
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Old 26-09-2012, 13:14   #8
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Re: OMC Zephyr Saildrive

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Originally Posted by _floater_ View Post
A friend tells me speed doesn't really matter and it changes with RMP only because it's driven by the motor itself. He says temperature is more important and that the thermostat could be used to trigger a relay to the pump, turning it on and off as required to maintain the right temp. (something like that..I forget exactly, but he said it would be simple).

Careful with that, remember the water also cools the exhaust and the rubber hose it lives in.

As an aside.......you may be the only one I know of that likes that engine
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Old 26-09-2012, 13:41   #9
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Re: OMC Zephyr Saildrive

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Careful with that, remember the water also cools the exhaust and the rubber hose it lives in.

As an aside.......you may be the only one I know of that likes that engine
Seriously. I don't just like it, I love it.
What are the usual complaints? I really don't have any other than stink.
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Old 26-09-2012, 13:44   #10
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Re: OMC Zephyr Saildrive

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Seriously. I don't just like it, I love it.
What are the usual complaints? I really don't have any other than stink.
In my experience, they've been cantankerous, smelly, loud, high consuming, unreliable things. But I've also only been around them in the salt water. I can imagine in the fresh water they're a little better.
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Old 18-02-2015, 09:16   #11
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Lightbulb Re: OMC Zephyr Saildrive


I have to do something this spring. The coolant output is getting really weak.
Several people responded to this thread with concerns over the flow rate not matching the engine's RMP. I have decided to fabricate a mount for an external waterpump which will be driven by v-belt off the top pulley, which currently drives the aftermarket alternator. Aside from experimenting with pulley diameter to get a reasonable water output, this will tie flow rate to engine RMP.
I understand this will rob power from the engine, but the saildrive easily pushes me at hull speed now and even a 25% decrease in power (should be less than that) will still leave me with all the power I require.
I have a few of these engines, all running, and this should keep me in low-maintenance propulsion for the remainder of my sailing life.
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Old 17-09-2015, 19:14   #12
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Re: OMC Zephyr Saildrive

hi, i used a similar motor setup, except it is a baldwin saildrive with the omc motor replaced by a 15.5 hp briggs and stratton motor.. the cooling for the wet exhaust was done by using an external chain driven jabsco water pump... Solved all my problems and the boat can stay in the water for most of any motor-saildrive issues
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Old 18-09-2015, 06:09   #13
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Re: OMC Zephyr Saildrive

Greetings and welcome aboard the CF, Filmtoys, and madmaxd.
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