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Cooling Question

Sleepwalker

Contributing Member
I have a closed system cooling on my V-6. Running on the trailer I have the sea water intake closed and run the freshwater hose into the strainer. I run it at the recommended up to 1200 rpm. When warming up I can see the temp gauge go up and then see the thermostat kick in. Using the gun I get a pretty steady 160d at the thermostat. (hose water temp here is probably in the 60's now) It has been running like this pretty regularly. When I launched today and ran off the raw seawater, idling at the dock same rpms (seawater also in the 60's), the temp hit 160 and kept climbing. I panicked at about 185 by the gun and shut her down. Hauled home, had lunch and hooked up the hose to run again and see what would happen. Temp climbed to 160 and stayed there. Ran it 20 minutes like that. I checked the strainer for any blockage/growth. I ran a snake down the line to the valve. I also back flushed thru the strainer, and got pretty clear water. Didn't feel anything going up into the valve either thru the hull strainer. I normally keep the raw water valve closed on the mooring, so the only fouling would be from the closed valve to the hull strainer. Any thoughts on why it would run normal on the trailer and hot off the seawater. Heat exchanger maybe? If so, why would the fresh water be different than the seawater, I would think it would overheat on either if there was a problem there.

Thanks, Rich
 
The only difference that stands out is that when hose fed, the raw water pump does not need to develop any suction to get fed water. When on the salt it must suck the water into the pump. The most likely problem would be in the pump and would be a worn or deformed impeller. While you are changing it also look at the cam that pushes in the blades on one side to be sure it is not worn. You may also (or even first) look at the input hoses to make sure they are not collapsing under suction.
 
Thanks John. Pulled the pump off today. Impeller looked pretty good but replaced it anyways. All back together, will fire up on the weekend and hopefully try and launch again next week. Will report back.
 
If your pump is belt driven then a loose or worn belt could also be an issue. The belt might slip under the greater load it sees when not hose fed.
 
I would also suggest not running the engine above idle while on a hose.

I'd make sure the hose has adequate capacity to keep things wet and that the strainer was always full...any air won't help the impeller.

The rear covers can also get grooved and cause poor performance. finally, the inlet plumbing has to be air tight or the cooling will suffer...
 
another check you can do is to measure the output of the raw water pump....not hard but can get a bit messy due to the water going around.

Disconnect the output and add a clear hose of sufficient length so you can easily control it...start it up and direct the hose into a bucket for 15 seconds then shut the engine off. mark the level of the water in the bucket or measure it if you want. repeat 3 times to get an average. then do the same with the hose feeding the pump. if that average is lower than your baseline, it means something has changed due to the setup...

if both configurations give you the same (nominal) product, then you need to check it with the OEM value for the pump.
 
Follow up. Changed impeller while I had the pump off (old one was still really good), took the ends off the heat exchanger and cleaned the tubes (though they were not bad at all), previously cleaned the intake strainer on the hull (that was not bad either). Launched today and no overheating.
 
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