Keel Cooled Yanmar

The 3HM was a raw water cooled engine. My installation which is original by the builder, 30 years ago, uses a keel cooled dry exhaust system. The boat is new to me and is on a trailer and yet to be launched. The previous owner said that the engine runs at 160 degrees and I am aware that raw water cooled engines run at lower temperatures. I am wondering if it would be possible or even desirable to do something to make the engine run at a higher temperature. The engine has two thermostats and I have not investigated yet if higher temperature ones are available.

Salt water direct cooled engines run at 160 degrees for a reason: salt begins to precipitate out at higher temps. Stick with your current thermostats.

You might pick up a point or so in efficiency if you ran hotter, but you couldn't measure it.

So stay with what you have.

David

Maybe I wasn't clear. My 3HM is keel cooled, no raw water, a completely closed system.

Many keel coolers require a bypass thermostat in the circuit.

This is installed between the cooler intake and discharge.

On a vehicle the radiator is sized to drop the coolant temp only about 20feg F.

A keel cooler , even here in FL will have the return water far colder than the engine needs.

About $150 -$200 or so, cast iron is fine as the coolant is antifreex , so wont cause rust.

A 180F unit will probably have the engine at 180 all the time.

The internal thermostat helps the engine warm up but will not compensate for too cold return water.

FF said:

Many keel coolers require a bypass thermostat in the circuit.

This is installed between the cooler intake and discharge.

On a vehicle the radiator is sized to drop the coolant temp only about 20feg F.

A keel cooler , even here in FL will have the return water far colder than the engine needs.

About $150 -$200 or so, cast iron is fine as the coolant is antifreex , so wont cause rust.

A 180F unit will probably have the engine at 180 all the time.

The internal thermostat helps the engine warm up but will not compensate for too cold return water.

Click to expand...

This makes sense but I am having trouble actually imagining the plumbing. Would this be a normally open thermostat in the bypass?

Sorry, when your OP said raw water cooled, my mind stopped processing when I saw the keel cooling. Raw water cooling implies raw water circulating through the engine jacket, not coolant that flows through a keel cooler.

But in any case, I am reminded by a Tony Athens recommendation to install 160 degree thermostats in high output Cummins engines. He said that it won't hurt anything to run a little cool, it gives you a bit more headroom in case of an overheat and the efficiency gain of running hotter is miniscule.

So, I wouldn't waste my time worrying about it.

David

"This makes sense but I am having trouble actually imagining the plumbing. Would this be a normally open thermostat in the bypass?"

The bypass is installed between the output to the cooling and the return.

It modulates the return water temp by stealing (by passing) uncooled water going to the keel cooler.

I would follow the engine Mfg instructions as to what is optimum operating temperature.

My boat has twin keel cooled/dry stack Yanmars, and they run at 160F. In the cold water here in Seattle the water coming back from the coolers super cold. they have a small bypass that is about a 3/8" hole that i think is mostly an air vent, but it does allow a little hot coolant to mix back in with the cold coolant coming back from the keel coolers. The boat is 27 years old, and the engine have around 2500 hours on them, and they both seem to run like tops, so I am not too worried about it. I did replace the thermostats with new Yanmar ones when I was changing out all the coolant, and hoses, and it didn't change the 160 temp.