In any engine, diesel or gas, the oil should be changed at the end of the season—before winter, not at spring commissioning. Dirty oil contains corrosives that will chew at your engine’s innards all winter if you leave it there.


Two fuel treatments, like Howe’s Lubricator and West Marine’s diesel stabilizer, should be run through the engine before the oil change.

Since the oil change will mark the last time you run the engine for any length of time this season, it’s important to treat your fuel system first. Here are the basic steps for the whole process.


Oil-changing gear: Jabsco changer, new oil, new filter, funnel, drip cup, oil-absorbent pads, rags, plastic trash bag.

1. With some room left in your tank or tanks, add your stabilizer and whatever other diesel treatments you like. I use the West Marine brand stabilizer and also Howe’s Lubricator (a trucker’s favorite). I run the Howe’s all season in a 96-hp Isuzu. The anti-gelling component of the Howe’s is important, especially if you run a biodiesel blend in cool weather.

2. Take the boat out for a final fall run. Make some turns and try to hit some wakes or chop to help mix the treatments with the fuel. Run long enough for the treated fuel to make its way through all the fuel lines and filters and into the engine.


Drain or pump out the old oil while it’s warm.

3. Go to the fuel dock, top up your tanks to the max (making sure your tank vent is clear) and screw down your fill cap hard, with a touch of grease in the threads. These are the most important moves you can make to keep your tanks free of water from both condensation and drip leaks. Water breeds Hydrocarbon-Utilizing Micro-organisms, aka HUMbugs, and bugs are a nightmare.


Swaddle all operations – like the removal of the old filter – with oil-absorbent pads.

4. Back at the dock, as the warmed oil settles into the pan, collect your oil-changing materials – a container for the used oil, oil-absorbent pads, rags, a funnel, and the new oil and filter. I put down a plastic trash bag under everything, and have a plastic cup for holding the dripping funnel and other oily bits. Oil-changing is an inherently messy business, so it’s vitally important to plan your moves, take things slowly, and avoid getting oil on the deck, the engine, and especially in the bilge. You can’t have too many absorbent pads and rags around.

5. There are a number of ways to get the old oil out. If you’re lucky, you have a full pump system installed, or you can drain the oil right out of the bottom of the pan through a hose with a nipple screwed into the sump drain. Unfortunately, most of us aren’t so lucky, and few bilges allow decent access to do this without the risk of a spill. So pumping the oil up through the dipstick channel is the next best thing. There are various hand pumps and electric drill pump attachments to get this chore done, but I’ve had good success with a purpose-built Jabsco system consisting of a small oil-resistant pump mounted right on a 3.5-gallon tank. The pump has clamp-on battery leads and an 8-foot dipstick tube.


Be very careful emptying the old oil out of the dead filter, and wrap the filter in an oil-absorbent pad and put it into a plastic trash bag.

6. Swaddle the whole operating area in absorbent pads and keep a rag in your back pocket. Here we go.

7. Remove the dipstick, take the cap off the oil fill, and (with an absorbent pad tucked underneath) unscrew the old oil filter a turn or two to break the gasket free.


Coat the new filter gasket with fresh oil.

8. Drain or pump out the old oil into the containers that will be taken to the gas station or recycling center. If you’ve used a sump drain, replace the plug and use a new washer if necessary.

9. With extreme care, finish taking off the old filter and drain that oil through your funnel into a waste oil container. Wrap the old filter in an absorbent pad and get it right into a trash bag. If you lean it against something and turn your back, it will fall over. (I speak from experience.)


Fill the new filter to the brim with fresh oil and screw it onto the engine. Don’t overtighten.

10. Lubricate the gasket of the new oil filter with fresh oil, fill the filter to the brim, screw it on the engine, and tighten according to the instructions. Usually medium hand-tight is right.


Add the new oil slowly and check the dipstick often.

11. Swaddle the oil filler hole with pads, and add the new oil through a clean funnel. Remember that oil capacities stated in manuals aren’t always spot-on. Note how much you took out, add slowly, wait for the oil to settle, and check the dipstick often. Don’t overfill.

12. With all the oil-changing gear cleared away, start the engine, run it for a couple of minutes, and check for leaks at the filter and at the sump if you’ve used the sump plug. No leaks? Turn her off. You’re done with that chore.

Now it's time to winterize the cooling system.

By the way, if you're running an outboard engine, winterization is just as important. Most of the concerns are the same, but here are five winterizing mistakes to avoid.

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