Marine Diesel Engine Checklist Before You Start Up

Before departure, our general rule is to check SIX items in our engine room: Engine oil, transmission fluid, belts & hoses, coolant level, raw water strainer and fuel filters.  Checking these items BEFORE you start up your marine diesel engine will not only extend the life of your pricey engine, but will also keep you and your crew safer. Captain John from wrote a good post about the step-by-step inspection of your engine before you hit the “start” button. All these things are really logical and happens to be the steps that we follow ourselves.

In addition to these important checks before you start your marine engine, keep a close eye on your maintenance log to note when key maintenance activities such as oil changes, air filter cleanings, propeller scraping, etc. are coming due. Below we list the six items that we check and is recommended by Captain John.

Learn more about how marine diesel engines work…fascinating animated model.


This video demonstrates checking your oil along with some other basics.

  • Oil level – Pull the dipstick out to wipe it off. Then push it back in fully. Pull it out a second time to ensure the oil level is above halfway but not above the fill line. Top off if needed.
  • Oil color, smell, and texture – The engine oil should be black as brown indicates excessive wear or contamination. Milkiness or streaks indicates water in the oil and the need for an immediate oil change.
  • free of debris as anything in the oil could damage the engine.
  • Graininess may indicate metal fatigue and certainly indicates a trip to the mechanic is needed. To look for impurities, smear the oil on your fingers and hold in the light.
  • Gearbox oil level – ensure it is consistent with the levels seen on the dipstick..

Transmission Fluid

Most transmission dipsticks screw into the engine so unscrew the stick and pull it out. Wipe it clean, then reinsert it so that the threads touch the housing (do not screw it back to check the level). Pull it out, check the level, and smell the fluid. Service immediately if you detect a burned odor. Screw the dipstick back to ensure no fluid loss.

Belts & Hoses

  • Visually check the drive belts for wear or other damage
  • Check for proper adjustment – Push in the middle of the longest part of the belt with direct pressure. The flex should be about 1/2 inch. Adjust or replace an ill-fitting loose belt may allow slippage and if too tight can result in excessive wear on the belts and components.
  • Tip: Carry belt and hose spares aboard.


Coolant or anti-freeze is vital to keep your engine from overheating and causing damage inside the engine leaving you stranded and resulting in incredibly expensive repairs.

Check only when engine is cool:

  • Header tank cap gasket – Remove the cap, flip it over, and visually check the gasket. If worn, broken, or missing a chunk, replace it. Without a tight seal that a good gasket provides you will lose coolant quickly and at the most inopportune time. 
  • Coolant level – Keep the level close to the top of the fill. Tightly replace the cap.

Raw water seacock & exhaust

  • Check your raw water filter – look for any muck such as seaweed, fish, jellyfish tentacles, trash, or other debris that may be obstructing the flow. 
  • After starting the engine, check the stern exhaust tube for a steady water flow. If blocked, check the raw water filter again and look for anything against the outside raw water intake.


  • Fuel level – ensure you have enough fuel
  • If you have a fuel shut-off valve, ensure it is set to the “on” position.
  • Check your fuel filters/water separators if you have clear inspection bowls.

Add years of life to your engine, save money on repairs, and protect your crew from most nasty mechanical surprises. 

More Diesel Engine Care Tips


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2 thoughts on “Marine Diesel Engine Checklist Before You Start Up”

  1. Thanks for these marine engine tips. My dad recently got a boat and is trying to figure out how to best take care of it. I think it would be smart if he took it into professionals to make sure everything was working correctly.

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