water flow

ignasty · #1 04-02-2009, 06:59 PM

when I purchased my boat the owner told me that he blocked off the outdrive from sucking water, so there is no need for ears ,all I have to do is run a hose into my seacock and I'll be fine. However when I drop in at the ramp in order for me to get flow I have to loosen the cap on my heat exchange to get flow and after that everything is fine other than I get my alternator covered with saltwater(goodtimes) But if my outdrive would suck water would that eliminate that problem? some one said its vapor lock and it happens a lot,doesn't seem right to me has anyone had this problem and is there a way to reverse the outdrive problem.

Rainmaker · #2 04-03-2009, 10:08 AM

I am not sure I understand what you mean when you say he blocked off the water flow. That does sound like a problem from where I sit though.

How does the engine cool when running?

ignasty · #3 04-03-2009, 10:47 AM

my motor is fresh water cooled ,plus it comes from my seacock. when I run the motor at my house I put a hose in my seacock which in turn gets pulled through my motor and comes out my out drive, But if I put a set of ears on the outdrive it will not suck water in because he blocked that off from taking water in , thats what i'm trying to explain I have no clue why he would do this I'm really not sure.

gss036 · #4 04-04-2009, 12:44 AM

I think I would be talking with a good mechanic and figure it out and fix it the correct way. Could it be the water pump that sucks water into the out drive is not working? I don't know, I have always run outboards, except a little 4 banger back in the mid 80's.

Runco · #5 04-04-2009, 09:50 PM

The outdrive pump has nothing to do with engine cooling on a fresh water cooled closed system. The raw water pump takes care of the engine. The outdrive pump should be retained as it helps cool the outdrive and the hose at the top of the outdrive is cut and just squirts the water out. I have the same set up on my Sceptre w/260 Mercruiser and it works fine.

Dilligaf · #6 04-04-2009, 11:31 PM

Quote:

The outdrive pump has nothing to do with engine cooling on a fresh water cooled closed system. The raw water pump takes care of the engine. The outdrive pump should be retained as it helps cool the outdrive and the hose at the top of the outdrive is cut and just squirts the water out. I have the same set up on my Sceptre w/260 Mercruiser and it works fine.

doesnt the fresh water cooled just cool the engine but the exhaust sides are still raw water cooled thru the outdrive intake correct?

Fr. Frank · #7 04-05-2009, 02:08 PM

Quote:

The outdrive pump has nothing to do with engine cooling on a fresh water cooled closed system.

NO! NO! NO! The impeller in the outdrive is what feeds water to the heat exchanger and in most cases, (if you have one) the raw water pump. If you don't have raw water pickups on the hull bottom, you desperately need good impellers in your lower unit. BTW, the outdrive has no need of cooling, it sits in the water.

Most fresh-water cooling systems use engine coolant just like a car, and in many cases, the engine coolant also cools the exhaust manifold. The raw water is injected from the heat exchangers into the exhaust risers after the exhaust manifolds, and then through riser to outdrive hoses.

However, there are still a lot of engines where everything after the cylinder heads going outward is raw water cooled. Most Mercruisers are like this.

I had a 255 Wellcraft SunCruiser with twin V6 stringer drives, and I have had a FishNautique with a Pleasurecraft inboard, and both used exhaust manifolds that were cooled by the closed cooling system. The OMC's actually used the exhaust manifolds as heat exchangers.

Water Rat · #8 04-06-2009, 10:18 PM

I have seen this set-up before where the raw water pick-up is transferred from the outdrive to a thru-hull fitting with seacock. IF you think about it (and your outdrive does not need the water flow for internal cooling, it makes sense in that if you had an issue, you have a means of shutting the ingress of water via the seacock (i.e. a busted hose or fitting).

The set-up would make sense to me on an engine/drive combo like mine,
a 7.4L Merc with Bravo 1. The Bravo drive has no water pump; the raw water pump is mounted to the engine and is driven by its own belt. It would, in theory, be simple enough to install a 1.5" or 2" through-hull to feed the raw water. Also, if you saw the plastic fitting on the inside of the Merc transom plate that the raw water hose attaches to, which is typically below the water line at rest, you might give the thru-hull/seacock idea a lot of consideration.

1bayouboy · #9 04-07-2009, 10:34 AM

The alpha's have impellers, the Bravo's don't. When you say you loosen the cap on the heat exchanger, is that the fill cap where you put in coolant??? I'm not sure about that...??? But essentially you have a big upside down U shape with one end being the seacock intake, then up through the strainer (if you have one) through the seawater pump, through the heat exchanger, through the exhaust elbows
(the top of the upside down U), and then down through the Y pipe out the prop. Without some kind of vent at the top, it's airlockd when you drop it into the water so water can't make it up to the seawater pump to prime it. When you use a pickup on the drive it's easier for the seawater pump to prime. You could install a strainer in your raw water path (above the water line but below the top of the elbow) and prime the pump from there......

I'm at a loss for explaining why loosening the cap (if you mean the coolant fill cap) would affect it....

Unless you correct it I would expect seawater pump impeller life to be pretty short....

1bayouboy · #10 04-07-2009, 10:42 AM

One more note....while the outdrives don't have explicit cooling, they do use the water flow for some cooling. In the docs describing how to install the blocking plate on the Bravo transom assembly to block off seawater flow, it describes how to position the hose so there will be some flow through the drive. I do long offshore runs with my Bravo and installed a drive shower that keeps it noticeably cooler.