I've been running and rebuilding Detroit 71s for 50+ years. Commercially and personally. Oil consumption can come from leaking turbo seal or bad rings. Keep the oil clean, maybe add a bypass filter....

You can sometimes find used parts at ebay.com or surplusman.com
With some searching, there are companies that make aftermarket intercoolers for many makes. Cheaper than from Detroit. Also there are...

Battery is too small. It will have a short life. Probably 2 amp charge, 1 would be better. I'd get a car size, deep cycle and keep it charged. It'll probably last 10 years.

I have a Minn Kota...

The fuel pump is mounted to the blower housing. It is driven by one of the rotors. The rotor bearing is lubricated by engine oil. If the fuel pump seal fails, pressurized fuel is sprayed into the...

There are 12v, 24v, 48v, and Ac 120v and 220v watermakers. Mine is self made, but similar to what's found here: https://www.cruiserowaterandpower.com/piston-pump-water-makers/
The high pressure pump...

Try https://www.surplusman.com/
They buy and sell engines and parts. They usually have Detroit engines, transmissions, and parts.
Also ebay.

An injector shop can test your injectors and rebuild as necessary. No real need for a 2nd set. You could have worn tips. When the fine holes get bigger, some or all of the spray becomes large...

White smoke could also be steam - water. But you would be loosing coolant. And that would be a head gasket failure, but not too common in marine Detroits unless they get hot.

I believe https://www.harbormastermarine.com/ has some parts, but probably newer models.
https://www.surplusman.com/ buys and sells used engines and parts.
ebay is a good place to look for parts...

Depending on the model, the fuel pump pumps 35 gallons an hour or more. It's a gear pump and should blow out any debris that went thru 2 filters. I doubt you have a return line clog. The fuel is part...

A breaker would stop all current to the motor. But a thermal protector could be in the motor or on the control board. Since the motor works again after sitting, I'm guessing it's a heat problem. I...

Is there a self resetting breaker in the line? If so, it heats up from too many amps and trips. Then it has to cool down to reset. Or the controller or motor could have an thermal breaker.
If the...

Probably a leak in the heat exchanger. Most of the time, the oil pressure is higher than the raw water, so only a little water transfers at startup. You should see some oil loss and a sheen in the...

The best way to save fuel and increase life of a Detroit is go slower.
Turbo Detroits have lower compression pistons than naturals. You'll have less power than you plan on.
Turbos fail because of...

Sometimes Sears a few parts like seals and gaskets.
A good marine store or ebay may have an impeller.
The motor wasn't built by Sears, just the name plate.
There are places on the internet and...

The fuel system is basically a closed system and should still be charged with fuel. I'd forgo changing fuel filters until after the engine has run. When you open the system, air needs to be bled out....

Looks like an expansion tank for coolant. Usually you have a pressure cap that keeps the coolant under 7-15psi. This appears to just be open to the engine. I would use something more that straight...

Do you have an inline relay? Most electric motors do. At full load the motor may draw too many amps for the relay. It trips and then cools down and self resets. You may have a weak relay that needs...

As with all electronic engines, you probably have to use a Mercury dealer mechanic for any issue with sensors and timing. Test equipment is probably proprietary. It's not a stock car engine with...

Probably galvanic corrosion with the salt water acting as the electrolyte. Your zincs need to be in contact will all the metal in your salt water system. For example, the engines should have zincs in...