Diesel engine servicing: the basics

Just like a car, a canal boat’s engine will also require regular scheduled maintenance. In fact, it’s worse than a car because that only requires a bit of an oil change every year or so these days whereas slow-revving marine diesels like to be refreshed and loved at much shorter spans.

My Lister-Petter LPWS4, for example, needed the oil changed every 100 hours. Think on that for a moment; if you do maybe 4 hours of cruising every couple of days, the engine’s going to need an oil and filter change after just 40 days – almost every month!

Granted the later version of that engine specified every 200 hours but that’s still 5 litres of fresh oil and a new filter every three months, and that’s the minimum service requirement. It also wanted a replacement air filter every few hundred hours and a new fuel filter too.

The good news is that even if you’re not mechanically-inclined (and believe me, when I started, I was not), this basic but essential task is surprisingly simple to do yourself, I kid you not. Once someone competent has shown you how to do it, I would urge you to do it yourself under supervision the next time and then after that you can do it alone without any issue. It will save you a fortune in mechanic’s fees.

Clearly, bigger issues – such as when the gearbox housing began to fall off the back of my engine – are something that you might only feel comfortable tackling if you have sufficient engineering expertise, but the basic regular service is a straightforward DIY task.

The gist of an oil change goes like this:-

1. Run the engine for 10 minutes to warm the oil. Don’t run too long else it’ll be absolutely steaming hot and you run the risk of scalding yourself either on the oil or the engine. You just want to loosen the old oil up a bit, to help get it out.

2. Turn off the engine. Probably worth laying a towel across the top as you may need to lean over it at this point and the engine will be warm.

3. At some location around the side of the engine will be a brass cylinder with a T-shaped knob at the top and what looks like a little brass spout coming off the side of the cylinder. This is a hand pump, built onto the engine, specifically for getting the oil out. Take an old, empty oil container and place its nozzle under the spout then pump the T-shaped knob up and down vigorously. This will pump the old (now warm) oil out into the container. Note: there will likely be a little shut-off valve half-way down the pipe coming off the bottom of the cylinder – this needs opening (usually turning through 90 degrees) to let the oil flow. You won’t get any oil out if you don’t do this.

4. When you have pumped so much that almost nothing else is coming out, and the old oil container is full of several litres of yucky black old oil, put that container down – with the lid on otherwise there’ll be a horrid mess when you knock it over later – and turn the shut-off valve back to its closed position.

5. Locate the oil filter which will be somewhere on the side of the engine. Oil filters are a circular tube usually quite squat and fat rather than long and thin. They are usually white and they screw onto the side of the engine. They are a) full of old oil and b) usually wound on too tightly by whoever serviced the engine before, so getting them unscrewed can be quite the performance. Try unscrewing it (beware old oil will dribble out so some folk like to wrap the filter in a plastic bag as they do this, to try to catch the drips). If it’s stuck tight, try wrapping something grippy like a thick elastic band around the filter and try again. You can also purchase special ratchets that are designed to grip filters (any branch of Halfords will have them). Or there’s a brute force method involving hammering a screwdriver into the filter and getting leverage that way, but it’s not the ideal solution.

6. Use a bit of rag to wipe the edge of the engine where the filter was mounted and make sure nothing from the old filter is stuck on (sometimes the rubber seal at the bottom of the filter gets too attached to the engine and doesn’t want to let go)

6. Take out your fresh new oil filter … wait, you did remember to buy fresh oil and a clean filter before you started this, yes? Wipe a little fresh oil around the rubber seal on the bottom of the new filter, then screw it – hand tight only! – onto the engine where the old one was. Some folk like to fill the new filter with oil before they do this but as you’ll lose most of it while you try to screw the filter in place, I don’t bother.

7. Unscrew the oil filler cap on top of the engine and pour in fresh engine oil of the correct specification[1]. Don’t overfill it, so go slow and use the engine dipstick[2] to check the level as you go, bearing in mind the oil will be gently oozing its way down so the level the dipstick shows you is usually not as much as you’ve actually put in (you’d need to wait a few minutes to let it settle before you’d get a true reading from the dipstick)

8. Once you have sufficient new oil in (so that it comes up beyond the ‘minimum’ mark on the dipstick), pop the oil filler cap back on. You can now start the engine which will push the oil around including through the new oil filter. You did remember to put the new filter on, didn’t you? Immediately look – just look, from above – to see if the fresh oil is spurting out from the filter because if it is, you didn’t tighten it enough. DON’T put your hands down the engine to change anything while it’s running in case they get caught by the alternator belt – this would cause you serious injury. Switch the engine off then do it.

9. You’ll almost certainly need to add a little more oil so turn the engine off, unscrew the oil filler cap again and add a bit more. Wait five minutes for it to dribble down to the sump, check the level on the dipstick then run the engine again. You can usually run it for five minutes or so as this is long enough for it to come up to temperature, for you to spot any leaks, and for any warning lights to appear on the instrument panel.[3]

10. Do not overfill! You do not want the level going over the ‘max’ mark on the dipstick! If you do, you’ll need to pump some out as you did with the old oil in step 3.

11. Congratulations! You just did a basic oil and filter service, the staple of engine maintenance. Honestly, as long as you do this regularly, your engine should go on forever, pretty much. Everything else is just icing on the cake. What engines really like is fresh oil.

[1] This will be given in the engine’s instruction manual. If you don’t have one, they’re usually online or the engine manufacturer will tell you. If you have an esoteric old engine, there are plenty of forums online with advice.

[2] Draw it out and wipe it clean with a paper towel before re-inserting fully and then removing it again to take a reading. That way any oil that dripped onto the stick as you filled the engine won’t give you a false reading. Remember to put it back in after.

[3] If they do appear, turn the engine off and work out what you did wrong. If you can’t, you probably need a mechanic to help.