How much water pressure when running engine out of the water?

[BradyA]

Hello there,

I've been browsing the forums for about six hours now and have not yet found an anwer to my question, so I decided to start a new thread.
I have a 1976 Rienell with a 1990 120hp GM engine and the original (but rebuilt a year ago) OMC Stringer outdrive. It has a water flush intake fitting on the top part of the outdrive, my question is this: How much water pressure through the flush fitting should I use when running the engine? Also, does the water going through the fitting pass through the impeller? I certainly don't want to risk running the impeller without water. Additionaly, if the water pressure is too high, can that cause a hydro-lock? Thanks in advance for any help!

 

[boatgrunt]

Re: How much water pressure when running engine out of the water?

Most manuals will tell you NOT to run the water on full strength. Personnally, I have done it several times without incident. It's hard to gauge the difference between low, medium and hard water pressure, but I would try to use "medium". The water will pass through your impeller and coolant system just like you were in the water. Watch the temp gauge closely and you should be fine.

 

[whywhyzed]

Re: How much water pressure when running engine out of the water?

Also, does the water going through the fitting pass through the impeller? I certainly don't want to risk running the impeller without water. Additionaly, if the water pressure is too high, can that cause a hydro-lock? Thanks in advance for any help!

It actually doesn't pass through the impeller with that adapter. Those adapters give you no indication of whether the impeller is good or bad.

I usually use moderate pressure and start the engine as soon as water is flowing and shut the water off when I stop the engine- that will pretty much eliminate hydrolocking potential. Not that it's really possible anyways, because the water only exits the sealed part of the manifold and riser and mixes in the exhaust once it's over the hump and falling down and out.

 

[BradyA]

Re: How much water pressure when running engine out of the water?

It actually doesn't pass through the impeller with that adapter. Those adapters give you no indication of whether the impeller is good or bad.

Thanks for all the great info! If the water doesn't pass through the impeller, will I damage it running the engine? I am not going to put the drive in gear.

 

[boatgrunt]

Re: How much water pressure when running engine out of the water?

Now I'm confused...I don't know how an engine can be cooled without the impeller spinning and sucking the water up into the engine. I am no expert but let's bump this one up and see if anyone can clarify. I'm pretty sure the water will be going through the impeller.

 

[lilsinker]

Re: How much water pressure when running engine out of the water?

You will get water to the impeller. On my stringer, I spliced a "tee" into the hose from the intermediate housing to the thermostat housing with a tee from a prestone flush kit from autozone. Costs about three bucks. I get water coming out of the water intake, both of the telltales, and the exhaust. I've passed this by a couple of OMC mechanics, and they say it'll work just fine. Just remember not to run the engine up past 1200 rpm or so and don't have it in gear for much at all. The coils (if it's an electric shift) are cooled by the water passing over the "bullet" while it's in the water.

 

[whywhyzed]

Re: How much water pressure when running engine out of the water?

Now I'm confused...I don't know how an engine can be cooled without the impeller spinning and sucking the water up into the engine. I am no expert but let's bump this one up and see if anyone can clarify. I'm pretty sure the water will be going through the impeller.

With this unique fitting, the water is supplied DOWNSTREAM of the impeller. The impeller still turns and is lubricated by the water flowing backwards in that area of the drive, but it doesn't pump it or suck anything.