universal M-25 diesel on sailboat Reality Check

Interesting history of the Universal Motor company at Catalina30.com/Techlib/Engines/History

Reality Check's diesel engine is the Universal M25, manufactured by Universal Motors and based on the Kubota tractor engine model D-850 (The M25XP is based on the D-950). Transforming a diesel engine into a marine environment is called marinizing and some interesting components have to be added to replace traditional functions.

Universal M25 diesel photos

Cooling a car engine - the radiator

Land based vehicle engines are cooled by means of a radiator. The radiator is a heat exchanger - the engine coolant (antifreeze + water) continuously circulates thru a radiator and the air rushing thru the coils of the radiator cools the coolant to keep the engine from overheating.

Boats don't have radiators

In the marine environment you can't use a radiator to cool your engine. The sea water replaces the cooling function of the air passing thru a radiator and a heat exchanger system replaces the radiator.

The diesel engine is cooled indirectly - by seawater!

Sea water is continuously moved through the heat exchanger via the "raw" water pump (aka saltwater pump, or sea water pump - the salt water pump is another "add on" to marinize the engine.) The fresh water coolant (antifreeze + water that cools the engine block) is cooled by flowing through a separate part of the heat exchanger that the cool sea water is passing through.

V-belt / Fan belt

The fresh water circulating pump is driven by the engine by means of the fan belt - there isn't a fan in the marine environment so it's sometimes called a v-belt - just look at the front view pic below and you see why.

The fresh water coolant is moved by the circulating pump through the heat exchanger, through the engine block, circulating pump and thermostat, back through the exhaust section of the manifold.

Exhaust system

The exhaust system is another interesting section - the exhaust from the diesel goes through a pipe called the exhaust riser or the exhaust mixing elbow. Why is is called a "mixing" elbow? Because the salt water from the heat exchanger is injected into the exhaust at this point, mixing the water with the exhaust to cool that hot exhaust down to eject out of the boat.