1976 120 hp mercruiser 4cyl

"I just purchaced a boat wit a

"I just purchaced a boat wit a 120 hp mericruiser engine. The engine needs an exhaust manifold gasket. How hard is this to do? Also Im confussed. There is a coolant resivore on top of the maqnifold with antifreeze in it. But it also takes in water from the stern drive. How does this work? Also how do I winterize this engine, and how do I get the water out of the lower unit, and engine so it doesnt freeze? Also there is no alternater on this engine. How do the batteries charge? The engine runs great except for being loud."

"from Your description, it sou

"from Your description, it sounds like You have a 3.7 litre engine.if so, the alternator is inside the harmonic balancer at front of engine. find out what You have, as the 120 is a totally different engine!"

"Then buy the applicable servi

"Then buy the applicable service manual.
You have a lot of good questions. Most of us here would be glad to answer any and/or all of them, but you'd be best off doing a little reading first.
It sounds like you have a fresh water cooled engine (Closed cooling system like a car, but you have a heat exchanger instead of a radiator). As long as there is a decent concentration of anti-freeze, the engine itself isn't in any danger of freezing.
The stern drive will drain itself when you pull the boat out of the water... the pick up screen on either side of the drive allows water to enter the suction of a small pump (impeller), drizen by the vertical driveshaft that feeds raw water through the heat exchanger then out through the exhaust elbows and back out the stern drive along with the exhaust.
There is (or should be) an alternator on the engine to keep your battery charged while the engine is running. It may not look exactly like a car's alternator... there are differences.
Replacing the exhaaust gasket isn't a tough job, but depends on how rusted the bolts are, and how much clearance you have to pull the rubber boot off the exhaust elbow and pull the elbow off."

"While you're changing the

"While you're changing the gasket, do a thorough inspection of the exhaust. Failed exhaust is the number one cause of turning your motor into an anchor."

"Failed exhaust is the num

"Failed exhaust is the number one cause of turning your motor into an anchor" ???
I would think coolant failure and lubrication failure would be the major causes of ruined engines.

"Nope,......
Rotten Exhaust

"Nope,......
Rotten Exhaust Manifolds dropping Saltwater Into the Motor,...
Kills Way More motors than Over-heating.....
And,....
Water in the Base, Isn't much lubrication to begin with,...."