Freshwater cooling for only part of engine?

[kiskadee]

I'm considering splitting my freshwater cooling so the freshwater loop does not include the exhaust manifold.

I have a 1980 Hughes 38 with a UJR that runs like new. She displaces 15,500 lbs and has a 14x9 two bladed prop. I sail in water that can vary from 40 to 60°F. On raw water cooling it can hold +6 knots all day. On freshwater it overheats if held above 5.5 knots for long. I have the Moyer Marine 160°F thermostat with spacer and a Robert Hess freshwater cooling kit. The raw water thru-hull is a 3/4" scoop strainer facing forward. It gets lots of raw water flow.

I still have the original Hughes water-jacket dry exhaust. Water from the heat exchanger is sent through the water jacket to cool the first 6' of dry exhaust. It is then injected into the muffler at the transom. It works very well and, with the engine below the cabin sole, it solves the water-lift problem.

I'm wondering if it's possible to bypass the manifold from the freshwater loop and have it cooled by the raw water that exits the water jacket exhaust? This water rarely gets above 80°F.

Could this work or will the temperature difference between the block and manifold cause problems with the manifold gasket seal or excessive carbon in the manifold.

Dana

[Al Schober]

Dana,
If you think your FWC is maxed out, taking the manifold off the loop will give the heat exchanger less of a load. Certainly worth a try.
IMHO, I don't think running the manifold cool will give you any problems. Mine has been running cool for 15 years....knock wood.

Al

[Mo]

Dana..call Mo

Hey there Kick Me Dee (that's his wife's name for the rest of you guys), it's Mo,

I'm home call me 902 four 61 1228....cell 902 four 83-8524 ...

[hanleyclifford]

Your idea would work but does expose the manifold jacket to salt water. If your raw water is only reaching 80 degrees F then your exchanger is not big enough for your application. Adding an exhanger in series is a better solution.

[kiskadee]

It's only money...

I'm still leaning towards trying to add the manifold to the raw water side. It's easy to drop my exhaust and look into the manifold, so I'll check it now and then for carbon build up.

I do agree that the best solution is a larger heat exchanger, but I was hoping for a free fix. It would be nice to have at least one pension cheque not have to turn into boat-bucks. Still, if you don't spend it then it's just coloured paper.

And yes Moe, I remember the alcohol induced name changes. One the VHF I was Kick Me Dee, and Dee was called Chickadee... More often than not, Al, "The Chief", could only remember the joke names!

[Dave Neptune]

Cold water?

kiskadee, one more thought. How long has it been since the engine or the exchanger have been acid flushed. With such cool water I would suspect it is time to flush or check the "shoe" in the pumps. Your system may need a good cleaning not modification. Just an FYI.

Dave Neptune

[kiskadee]

I've been leaning that way Dave. I haven't opened the heat exchanger ends in a couple years. She sat bypassed for several months with raw water in it, so there may be critters growing in there. I'll open 'er up next week when I'm back to the wet coast from the right coast.

A friend solved an intermittent cooling problem last month. It was a small clam in the inlet thru-hull. When the clam was shut he had cooling. When it was open he had almost no water flow. It was found by a diver who was cleaning his hull.