Almost off topic, please delete if deserved.
A nephew has a skiing boat, inboard engine and asked me for suggestions to cure steam from the exhaust that did not show before. All spark plugs normal, engine temperature normal, running very normal.

I suggested that steam comes from exhaust temperature raised, seawater cooling flow diminished, or both; the heat exchanger, strainer, hoses, passages to be inspected and cleaned from corrosion or debris build-up restricting flow.

Shortening the story of diagnostics, steam disappeared by replacing a dirty gasoline filter. And runs more powerful than ever.

Can someone explain ? Can Discos experience something similar or the oxygen sensors/ECU would compensate leanness from an obstructed fuel filter? -If running lean was the cause that I can think of-
Next... when was the last time we replaced the fuel filter ? Are we forced to replace a fuel pump assembly that runs well to ensure good fuel flow ?

 

You can pull the pump and clean the filter screen on the bottom in about an hours time.....you will want less than a 1/4 tank of fuel in the tank for obvious reasons. Most boats dont have all the emission electonics on them so its hard to compare them to modern cars .

 

Had a 21ft V8 Chevy ski boat for years, injected. When I bought it the piston lands on the top of the pistons were all cracked, valves were all mushroomed. Internet research revealed it to be a common problem on that vintage boat due to water in the fuel causing lean running. Problems started to be common with advent of E10 fuel. Absorbs water in the tank, water separates out, engine runs lean and damages valves and pistons. No oxygen sensors, so AFR could go lean. Your nephews boat sounds carbureted, so it could go lean also. Lean means higher combustion temps, higher engine temps, but boats have ultimate cooling systems. Also, exhaust manifold could have cracked, pump would push water in to the exhaust.

Discos would not do that due to closed loop fueling, ECU would adapt until it ran out of fuel trim adaptability.

 

Could have been running lean. Not enough gas. Not an expert but just a guess