How Are Boat Engines Cooled?

[rbattelle]

I know they're liquid cooled, but I don't understand how they interact with the lake (or sea) water. Are they open loop, with water being pumped in from outside, run through the engine, then discharged? Or do they have closed systems with a water-water heat exchanger?



-ryan

 

[JApol]

inboard or outboard?



OUtboards take water from the lake/ocean swish it around a little and spit it out. Inboards?

 

[TORQUE THIS]

There are 2 systems, water is pulled thru the lower unit (I/O or Outboard) or a thru hull fitting (Inboard) cycles thru the motor and then is discharged with the exhaust thru the center of the prop, or another discharge port.

The other system is a closed system using a special marine coolant. However, sea water is pulled in the same as above but thru a heat exchanger and then discharged.

The second system has proven to work great with salt water, being that salt water is very harsh on a marine engine.



I trailer mine, 17' with an I/O. After EVERY use, it is flushed in the driveway for 10 minutes. We launch in salt water...

 

[midlife crisis]

Yes, Sterndrive (I/O)engines are typically cooled by the type water the vessel is in. Some manufacturers do offer a Fresh water system as an option. This system also varies between manufacturers ie: some cool block & heads & manifolds,("Full") and others just the block & heads ("Partial").



Volvo has introduced a system on their sterndrive gas engines that introduces a salt neutralizing solution, used when the engine is "done for the day". Quite effective, and much cheaper than FWC.



Diesels -Inboards & I/Os (except for sailboat auxilliary's which are typically raw water cooled)) are typically FWC.

As stated above these utilize a "Tube Style" or "Bundle" heat exchanger as a water to water radiator. The incoming sea water will typically cool the H. E. , the aftercooler, and the trans oil cooler, and quite possibly the engine oil cooler-but that varys per mfg.

Bigger diesels found in Draggers, Tugs, and larger commercial vessels are typically "Keel Cooled". The boat has a "grid" under the hull, which acts like a heat exchanger. This system is closed, so the engine has coolant on one side, and the KC loop has coolant on the other.

 

[JLEONARD]

On a Cummins B or C engine, the raw water pump bolts to the engine instead of the power steering pump. It is gear driven the same way. From the sea water outlet, the water flows thru a fuel cooler (some may not have this) then thru a seperate cooler for the transmission oil, then into the main heat exchanger. This is a tubular unit that is clamped to the outside of the exhaust manifold, with a tube bundle inside. The sea water then dumps into the exhaust riser which sprays into a rubber exhaust hose. The water exits via the exhaust... (I had a 5 inch exhaust on my 270 Cummins and it was about 1/3 water)

The exhaust manifold is coolant filled, as is the turbocharger, and the turbo is mounted at the rear of the manifold.

There may be a sea water intercooler in line as well on the higher hp engines.

On the front of the engine mounted at the highest point there will be a stell expansion tank for the coolant and an overflow bottle.

Jay

 

[rbattelle]

So do open-loop systems ever permit the engine to come up to full operating temperature? Seems to me they'd always be at the temperature of the outside water...



-Ryan

 

[Hohn]

Yes, they do. In cold water, the open-loop just cycles like our engines do.



These engines have thermostats, too.



That's why a flush is so important after saltwater usage. If you don't run it until the t-stat opens, then you have saltwater trapped in the jackets-- which, as you might guess, is BAD.



jh

 

[TORQUE THIS]

Mine runs about 140* to 160*, water temp in upper 60's to 70's till mid June, when the river is is up to 80*, the boat runs around 180*, to 190*.

 

[rbattelle]

So the open-loop systems still trap water within the block (behind a thermostat). Okay, I think it all makes sense now... thanks guys.



-Ryan

 

[Hohn]

Well, not all have t-stats. Our Mercruiser did, iirc. It was 17 years ago, though

 

[Joe G.]

The sea water side of the heat exchanger uses zincs as sacrifice metal to reduce corrosion. On the 671 screamer we had there were two zincs in the heat exhanger tank that we changed every year.

 

[JLEONARD]

An "open loop" system which I'm assuming is what is normally called "raw water cooled" uses raw which could be sea water in the block. These engines usually have a 140 or 145 F thermostat because salt water will start to crystallize at around 160 F ... so the temp needs to stay below that or things will start to get plugged up. (Mark check this out on your boat)

On the closed loop side (called "fresh water cooled"), my Cummins had a 190 T stat and would run there unless the sea water was cold and the engine was loafing along... then it might run as low as 170 or so. At WOT really pushing it would run at about 195 and stay there. (and post turbo EGT would be just shy of 900 F)

Jay

 

[C. Harlan]

I have a 1998 Malibu Sportster Ski boat with a Carbureted 350 Chevrolet motor, and it is a fresh water system. When idling it runs about 150°-160°, and when up at around 3k-4k RPMs it will run about 180°. . It has a draincock on the side of the block to drain off excess water in the winter time to prevent the block from freezing. . pretty cool, eh?



-Chris-