Change Trans Fluid on a 1978 470 MerCruiser

[Tacoma_Dave]

Howdy everybody,

First post but it certainly won't be the last as I'm unfamiliar with motorboats. My wife and I just purchased a 21' 1978 Cuddy Cabin that has a 3.7 MerCruiser engine. Now I know my way around automobiles (all sorts of repairs and swaps), but I am unfamiliar with marine engines. First thing I always do when I get a used car is to change the fluids no matter what. I want to do that with this 3.7. I know about the oil (got the pump coming any day), but for the life of me, I cannot locate the transmissions dipstick and where to drain! Any help would be greatly appreciated. Thanks again folks and take care.

 

[Eric 3.7LX Alpha 1]

I cut the side out of a gallon sized Prestone antifreeze container, and squeeze it under the drain plug, and drain mine by gravity, it just fits.

There is no transmission. It should be bolted to an outdrive as I don't think the 470/3.7's were used on inboards. What's the serial number of the engine and outdrive? The 3.7 and 3.7LX were first used in '88. The earlier version of them was called a 470, which is what it would have been if original from '78.

They are a Mercruiser marine engine based off a Mercruiser aluminum block mated with a Ford 460 iron head, connecting rods, pistons and flywheel. They are sensitive to overheating due to the different expansion rates of the two metals, usually resulting in a blown head gasket. You will want to have a good temp. gauge at the helm, and change the impeller in the outdrive ever few years. I have a temp. gauge built into my radiator cap also, so I can verify the dash gauge and when working back at the engine. The earlier models came with a 3" diameter heat exchanger, later upgraded to a 4", which is the one you'd want.

The factory charging system on these use a stator which is bolted under the harmonic balancer. It uses a water cooled voltage regulator that when fails, usually causes high voltage to the battery. The best fix is an aftermarket belt driven alternator kit. They never came with a belt driven alt.

 

[Tacoma_Dave]

I cut the side out of a gallon sized Prestone antifreeze container, and squeeze it under the drain plug, and drain mine by gravity, it just fits.

There is no transmission. It should be bolted to an outdrive as I don't think the 470/3.7's were used on inboards. What's the serial number of the engine and outdrive? The 3.7 and 3.7LX were first used in '88. The earlier version of them was called a 470, which is what it would have been if original from '78.

They are a Mercruiser marine engine based off a Mercruiser aluminum block mated with a Ford 460 iron head, connecting rods, pistons and flywheel. They are sensitive to overheating due to the different expansion rates of the two metals, usually resulting in a blown head gasket. You will want to have a good temp. gauge at the helm, and change the impeller in the outdrive ever few years. I have a temp. gauge built into my radiator cap also, so I can verify the dash gauge and when working back at the engine. The earlier models came with a 3" diameter heat exchanger, later upgraded to a 4", which is the one you'd want.

The factory charging system on these use a stator which is bolted under the harmonic balancer. It uses a water cooled voltage regulator that when fails, usually causes high voltage to the battery. The best fix is an aftermarket belt driven alternator kit. They never came with a belt driven alt.

This is awesome info. Thanks Eric, much appreciated. Yes, it is a 470...I just saw a lot of info that seemed to use the 2 interchangeably. I can't really make out the serial # on the engine's valve cover and I don't see any numbers on the outdrive. Thanks again for the info my friend. Here's a few pics...

 

[Eric 3.7LX Alpha 1]

Your outdrive model is called a MC-1. It was made before the Alpha One drive, many call it a pre-Alpha, but there were a few models before the Alpha One so the correct name is best. I have an MC-1 as a spare, and have some photos of where the serial number would be. The engine should have a plate riveted on the port side of the engine next to the heat exchanger.

 

[Tacoma_Dave]

I'll check it out. Gracias Amigo.