100 Hours or Bust - The Golden Rule of Boat Oil Changes

My first car was a used Ford Escort station wagon. It was purple and it was well broken-in. About six months after buying it (and driving it literally everywhere), I decided it needed an oil change. I had no idea what an oil change would do for the vehicle, but I had heard someone mention something about it once. I thought maybe I’d look into a ‘tune-up’ at the same time. The whole thing felt very adult.

Much less adult was my reaction when I was informed that oil shouldn’t be thick black sludge, and that the cost to remedy the sludgery was far more than I expected. Lessons were learned: engine oil should be checked regularly (for colour and for volume), and it should be changed on a regular schedule. Who knew?

So, why should boaters spend time worrying about oil? The answer is pretty simple: whenever metal parts are moving together, lubrication is required to keep the parts moving freely. The metal parts must also be kept cooled, relatively speaking. Without oil, these parts grind and eventually seize. All engines (including marine inboards, outboards, and sterndrive engines) have fast moving parts that create huge amounts of friction and heat. The engine oil exists to reduce that friction. In terms of timing, oil changes in cars are done based on the number of kilometres driven. In a boat, timing is based on the number of hours that the engine has run.

Understanding The Function

An engine’s lubrication system is pretty simple on most marine engines. An oil pump (typically a simple mechanical pump) pulls oil from the lowest part of the engine (the oil sump) and forces it through a filter where dirt and contaminants are strained, before moving through all the galleries and channels where lubrication is needed. The oil is under pressure as this happens, and many boats will have an oil pressure gauge at the helm giving you a visual indicator of the engine's oil status. Too much pressure means that either there is too much oil, or the oil has become badly contaminated. Too little pressure means that there isn’t enough oil in the system, or it has become diluted in some way. By ensuring you have clean, quality oil, the engine will have better starting ability and less friction. The formation of rust is also minimized or prevented, contaminants are removed or minimized, the engine operates as the proper temperature, good compression is maintained, and fuel burns at an expected and consistent rate. In short: having the right quality of oil, in the right quantity, with the right filter is the key to keeping your engine running well.

Choosing The Right Oil

Choosing the right oil can be daunting. There are lots of types, brands, and numbers. If you don't know what they all mean it can be very confusing. What do those number mean, and how do you know which oil is right for your engine? Here is a crash course:

Engine manufacturers specify the type of oil to use. They determine the type through rigorous testing done during engine production. It is NOT just a made up number, or a case of ‘any oil will do.' Using the wrong type of oil can affect your engine performance drastically and cause damage. The oil type can be found in the engine service manual, on the engine specification plate or sticker, or by contacting an authorized dealer. For example, your engine may call for SAE 30, or 10W30, although there are many types.

Manufacturers also specify the frequency of oil changes in their service manuals – the general rule of thumb, though, is 100 hours, or once per season (typically done just before haul-out, or just after launch). I recommend changing oil in the fall. This ensures that contaminants aren’t left in the engine all winter, and that the engine will be at its best form for re-starting in the spring.

How To Do It

Marine engines have two access points for oil: the oil fill, and the oil dipstick. The oil fill is a cap which can be removed to add oil. The oil dipstick, when pulled from the oil sump, will show the quality/colour of the oil, as well as the oil level. The appropriate operating level should lie within the hash marks on the dipstick.

When checking the oil level with the dipstick, it is important to note the colour of the oil: it should be a honey-golden colour. Black oil indicates contaminants in the oil. Grey or white oil indicates water in the oil – which can cause many unwanted problems. With boats, water can enter the engine system if the water level in the bilge is too high (entering into the sump at the bottom of the engine), or through a blown seal or gasket in the engine. In each case – black, grey, or milky colour – the oil should be changed immediately. After changing the oil, run the engine lightly, and then check to ensure that the oil remains clear after running.

Oil Changes the Right Way – Step-by-Step

1. Ensure that there is oil in the engine, and that it is not a danger to run the engine to operating temperature in its current state. I recommend doing this while the boat is in the water, so that the engine can be run long enough to warm the engine and oil.

   
   

2. Check the engine manual, or with an engine dealer, to determine the correct oil type and oil filter for the engine (don’t trust that the oil filter currently on the engine is the right one!). Make sure you have correct quantity of oil as well.

   
   

3. Get tools ready. You’ll need an oil extractor, oil in the right amount and grade, oil filter, oil filter wrench (the oil filter may be tight on the engine), nitrile gloves, and paper towels. You may also need to reference your engine’s manual for oil, filter, and procedure information.

4. Start the engine and run it to operating temperature – this warms the oil and allows it to run smoothly – and will allow you to extract it easily.

5. Unlike a car, most marine engines don’t have a drain plug that is accessible to allow the oil to drain. Instead, oil must be pumped from the engine, using an extractor with a tube inserted into the dipstick tube. The extractor handle is pumped, building pressure, and sucking the oil up the dipstick tube into the extractor. Check the level in the extractor to ensure that the proper amount has been drained before finishing this step (i.e., if the engine is designed to hold 7L of oil, but you’ve only extracted 4, there is likely still oil inside the engine).

   
   

6. Once all the oil has been removed, the oil filter can be removed and replaced. Most are spin-on type (to loosen, turn the filter to the left. To tighten, turn it to the right). You will likely need an oil filter wrench, as the continual heating and cooling of the filter can cause it to seize tightly to the engine. There are many mounting configurations – some are top-up, some are top-down, others are mounted to the side. All are equally messy. You may want to wear nitrile gloves, and wrap the end of the filter in paper towels – it’s also a good idea to wedge a container below the filter as it is removed, so that you don’t make a mess in your bilge. Once you have collected all the oil in an appropriate container, make sure it is stored safely until you can dispose of it properly.

   
   

7. Open the fresh oil container and using a finger, smear some fresh oil on the rubber gasket of the new filter. This will aid in keeping a seal, and in removal next time.

   
   

8. Spin on the new filter, and hand-tighten it. Don’t overtighten, as the filter can be damaged, and will be difficult to remove the next time!

9. Open the fill cap, and using a funnel, pour fresh oil into the engine. I tend to stop every 2L or so and check the level using the dipstick – this ensures that the engine isn’t overfilled – and allows the new oil to settle. Continue filling until the oil level is close to the full marks on the oil level dipstick. Pro-tip: Take your time. Oil needs to settle into the sump to be read accurately. Don’t rush the process.

   
   

10. Replace the cap, dipstick and clean up any excess oil or spills. Run the engine for a few minutes. Once the engine has cooled, re-check the level and colour on the dipstick.

    
    

Enjoy the remainder of the season, or 100 hours, whichever comes first. #tips