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Thruhull Raw Water cooling

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thomasr

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I'm restoring a Sea Ray 26

I'm restoring a Sea Ray 268 which has a 454 Mercruiser with a DP 290 drive. I replaced the raw water pump but am thinking about using a thru-hull bronze fitting to take the cooling water direct and not through the outdrive. Has anyone done this and what are the pros and cons.
 
It's better IF it's do

It's better IF it's done right. (The old impeller must be removed or it will shed blades.) Is there a 'go-by' boat with a similar system nearby for you to figure how to arrange things?

Jeff
 
"There is no impeller in the o

"There is no impeller in the outdrive since it uses as belt driven raw water pump, but the water comes up through the outdrive. This is a unusual combination because someone put this DP 290 on a Mercruiser 454. It appears to have been done professionaly. It just seems to be that getting the raw water independent of the outdrive would be better. I'm not sure where to put it but it would be in bilge area somewhere not to interfere with the trailer bunks. Any suggestions would be appreciated.

Tom"
 
I haven't seen one of thes

I haven't seen one of these boats configured this way so I have nothing to go by. I've heard that some of the older volvo drives cause cooling problems due to air leaking into the system as the engine driven pump brings water up through the plumbing in the outdrive.
 
I'm with Tom. You wouldn&#

I'm with Tom. You wouldn't believe how air sucked into a raw water pump can screw up cooling!

Jeff
 
"Both through-hull and through

"Both through-hull and through-outdrive cooling have pros and cons. With the through-outdrive cooling system, if a piece of plastic gets trapped in the outdrive water suction grid or if you have a damaged water hose connector, you have to be quick to stop the engine or it will quickly overheat. But if one of the raw water pipes or hoses fails on the suction side of the system, you won't get water ingress in your boat due to the shape of the raw water pipe on the inside of the transom shield, which is just above water level.

On the other hand, through-hull raw water cooling means that the suction side system is always full of water and it is more difficult for the hose to become plugged with a piece of plastic, but you will be more prone to catch small debris (make sure you use a raw water strainer before the raw water pump, and that there is an isolation valve installed between the strainer and the through-hull fitting). On the negative side, you have to make a hole in the bottom of the hull to install the through-hull fitting, and if either the fitting or the hose attached to it does fail, then you will flood the boat's engine well.

Personally, I am happy with the through-outdrive cooling system. But if I had a boat with through-hull fitting, I would make sure I had a large bilge pump (or even better, two pumps) installed and that they work well, because the chances of flooding the engine compartment are larger than with through-outdrive cooling. A couple of wooden plugs may also turn useful in an emergency.
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"Thanks for your ideas. I thin

"Thanks for your ideas. I think I will go ahead and reseal the outdrive and see if I have any problems. Then if I run into cooling problems I can always put in a thru hull system later.

Thanks,

Tom"
 
have done this job many times.

have done this job many times.Placement of water pickup on the hull is the important part. What you will need is a bronze scoop style thru hull fitting. ball valve to fit on it and hose nipple. All 1 1/4 in. I believe but east to confirm by measuring the water intake hose.Might want to consider a raw water filter also.
As engine rooms are usually pretty tight thought must be given as where to install thru hull. has to be in a location that is accessible for instllation and to be able reach handle of ball valve if needed. Height of fittings and hose routing must also be considered. As for placement conserns on hull --as close to center of hull as possable and insure that there are no obstrustions forward of it. You must invision water flow at planing speed and place scoop in a area where it will be in clear water to avoid poor water flow due to cavatation.
Lastly dodn`t forget - when mounting thru hull to use a wooden backing plate on inside of hull and to be generous with bedding coumpound.

Job uill take a bit of forethought but will be worth it to improve water flow and cooling.
 
"BJ,

Thanks so much for the

"BJ,

Thanks so much for the info. I've already research the bronze scoop fittings and mine is 1 1/4. If I decide to do this I will follow your recomendations.

Tom"
 
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