Removing and replacing oil and filters
Before changing the oil, an engine must be run until the oil is hot. This lowers the viscosity of the oil (makes it as ‘runny’ as possible) to make it easier to remove and ensures that almost all of the oil drains down out of the various oil passages. Note that in general when an engine is running and has warmed up the oil temperature should be at least 100˚C (212˚F) in order to boil off any condensed water in the oil.
When you pump the oil out of the engine, it will probably have cooled down below the boiling point of water. But it can still be hot enough to cause burns. Please be careful and wear gloves if neccesary.
When removing the oil, an oil filler cap should be loosened to allow air in as the oil is sucked out.
When an oil change is initiated, it is important to set aside the time, and have the materials and tools on hand, to finish the job. Nigel has three times in his career become distracted after draining the oil out of an engine and then forgotten to finish the job and cranked the engine. Two engines survived but one, a 2,000 hp compressor engine on an oil production platform, did not!
Pumping out the old oil
A permanently installed oil pump is a great feature
Once an engine is installed in a boat, the drain plug in the bottom of the engine pan (sump) is typically inaccessible. Ideally, prior to engine installation the plug will have been replaced with a fitting and a hose led to an oil change pump, either manual or electric (12V or 24V), with a discharge hose from the pump that enables the old oil to be pumped into an appropriate container for disposal.
If there is any way to have such a system installed on an engine that does not already have one, it is well worth doing. It makes oil changes easy. The hose from the base of the engine to the pump must be suitable for hot oil and ruggedly built; if it should fail with the engine running the engine will run out of oil and likely be destroyed before the operator has time to react.
Oil change pump - halfway up on the left - being used to pump out old engine oil
Oil change pump plumbed to three engines – two propulsion and one generator – with the relevant engine selected by opening the valve at the base of the pump. The coiled hose is used to send the old oil to a container for disposal and to then pump in the clean oil.
Absent an oil change pump, the oil is typically sucked out through the dipstick tube. Most of these tubes go to the bottom of the crankcase and as such if a hose is slid over the tube tightly enough to create an air-tight fit, the oil can be sucked out through the dip stick tube itself. Typically, these dipstick tubes have a belled fitting near the top which is designed to make a tight seal with a hose pushed down from above.
Sometimes the dipstick tube does not go to the bottom of the crankcase, in which case a small plastic tube must be fed down inside the dipstick tube. If the plastic tube has previously been coiled (which is typically the case) and it now has residual bends, it will be difficult to get it all the way to the bottom of the crankcase without the end of the tube curling up out of the last of the oil.
The quantity of oil pumped out should be more-or-less measured to ensure it correlates with the specified amount of oil in the engine. Extracting oil this way can be a frustrating business! You may have to move the plastic tube up and down while pumping to make sure you really are at the bottom of the crankcase and have extracted most of the oil. There will always be a small amount you cannot get.
Hose being pushed over a dipstick tube for oil removal
Portable electric (12V and 24V) oil change pumps can be bought from marine chandleries, but these can be awkward and messy to use. Nigel prefers manual vacuum pumps with a built-in chamber for collecting the oil and hauling it off the boat for disposal.
This kind of manual vacuum pump – being used here to pump diesel out of a contaminated fuel tank – is excellent for oil changes.
Portable 12V pump being used to suck out engine oil
Changing the oil filter
The oil filter should be changed at the same time as the oil. Almost all oil filters are the screw on canister type. An appropriate wrench will be needed to loosen the filter. As with fuel filters, a correctly sized metal band wrench will be far easier to use in difficult spaces than a universal strap wrench.
Some oil filters are really hard to access. For many engines it is possible to buy a remote filter kit. The filter is removed, and adapter screwed in its place, and hoses brought out to a new filter base located wherever is convenient.
Many filters are mounted horizontally, and some vertically with the open end at the bottom. In both cases, as soon as the filter is loosened it will spill dirty oil. Something will be needed to catch the oil. This is another job for which diapers come in handy!
The filter will be too hot to comfortably handle so a pair of gloves is advised. If it is a horizontal filter, as soon as it is initially loosened with the wrench, and before it begins to leak substantial amounts of oil, it may be possible to wrap a heavy-duty resealable plastic bag around it to catch any more oil that spills as it is undone by hand and dropped into the bag.
This kind of universal strap wrench is hard to use in tight quarters.
Diapers will hold a surprising amount of spilled oil.
Much better is a properly sized metal band wrench.
Using a heavy-duty resealable plastic bag...
...to minimize oil spills
Once the old filter is off, make sure its sealing ring is not still stuck to the engine block. The new filter will come with an embedded sealing ring. If the old ring is still in place when the new filter is installed the old ring will be squeezed out sideways and the engine will spray out copious amounts of oil as soon as the engine is fired up.
The new oil filter should be purchased from the engine manufacturer to ensure it has the appropriate internal construction. Nigel likes to write the date and engine hours on it before installing it. The filter may have a plastic seal over its open end. If so, be sure to remove this before installing it!
The sealing ring is lightly lubricated with clean oil and then the filter is screwed on by hand until tight. There should be instructions printed on the canister as to how much more to tighten it, using the appropriate metal band wrench. If not, it will be between a half and three quarters of a turn. It is important not to overtighten the filter for two reasons: (1) it is possible to do internal damage, and (2) it will be hard to remove at the next filter change.
Lightly lubricating the seal on a new oil filter prior to installation
Adding clean oil
Different brands of oil with the same API or ACEA classification may use different additive packages to meet the various engine performance category/specification requirements. For the best results, do not mix oil brands. Mixing of brands may also generate confusing oil analysis results. However, in the absence of the usual brand it is far better to top up a crankcase, or perform an oil change, with a different brand than it is to neglect basic maintenance.
If the engine has an electric oil change pump, it will likely be reversible. In this case, the oil change pump's discharge tube is inserted in a clean oil container and the pump used to transfer the oil to the engine. This makes oil changes easy with no spills.
Absent this pump, there will be one or more oil fill caps. There is almost always one on the top of the engine in the valve cover, but there may not be sufficient headroom to pour in oil. There is typically another on the side of the engine. The area around a cap should be cleaned before removing it to avoid dirt being knocked into the engine. A funnel is more-or-less essential if you want to add oil without spilling any, especially if there is any boat motion.
A funnel will be needed to put in new oil, plus sufficient access to do this
The dipstick will have a low and high level; fill to the high level and no higher
Many oil cans come with a foil seal. This has to be removed. Be careful not to knock or drop pieces of foil into the can.
The engine manual will specify how much oil is needed. In most cases oil is added until up to the top mark on the dipstick. You will not have removed all the old oil, so don't immediately pour in the total volume specified in the manual! Pour in a quart (liter) or so less than is specified, give it time to drain to the crankcase, check the oil level with the dipstick, and then add more as necessary. Any level on the dipstick between minimum and maximum is OK for engine operation, although you want to be closer to maximum to allow for oil consumption. If you overfill, you need to remove the excess because it is possible to do serious engine damage with an overfilled crankcase.
If the engine is installed at an angle, and the dipstick is not at the center point along the length of the crankcase (pan; sump) the dipstick may not be accurate. the engine manual may have angle compensation data. If not, the first time the oil is changed, assuming all the old oil has been removed from the engine, the specified amount of new oil is added and then the dipstick marked to indicate the appropriate level.
Before starting the engine, make sure the dipstick and oil fill cap have been replaced. If the former is left out but the latter is in place, and the dipstick tube goes to the bottom of the crankcase, when the engine is running all the oil can be pumped out of the dipstick tube! If the latter is left off (the fill cap), especially if it is in the valve cover, a considerable amount of oil will be splattered over the engine. Guess how we know!
Large engines often have a pre-lube pump. This is used to fill the filter and restore oil flow to the bearings before cranking the engine. Smaller engines do not have this - they are simply cranked, although on some with a manual shut down (a knob in the cockpit which is pulled out) the engine can be prevented from firing and prelubed by cranking for 10-15 seconds. In the absence of prelubing, as soon as the engine fires up the oil filter will almost immediately be filled and the engine pressure will return to normal.
Take a close look around the seating area of the oil filter to ensure there are no leaks. Remember, the engine is running so stay clear of pulleys and belts and hot regions of the exhaust system.
Oil change miscellanea
Some engines with a turbocharger have a small oil filter in the oil feed to the turbocharger bearings. If so, it is important to identify the filter and change it at the specified intervals. If the turbocharger is starved of oil at any time, rapid and expensive damage will ensue.
The injection pumps on some decades-old engines which are still in service (for example, Ford Lehman engines and some of the early Perkins/Westerbeke engines) have an oil sump which requires a periodic oil change.
Transmission oil
There are fundamentally two types of transmission (gearbox) – mechanical and hydraulic. Hydraulic transmissions incorporate an oil pump which generates the pressure needed to operate clutches. The oil system may well include a small oil filter. If so, this is something you need to identify and to clean or replace when the oil is changed.
All transmissions have an oil sump and oil that is separate from the engine. The transmission may require the same oil as the engine or else transmission fluid (automatic transmission fluid - ATF).
Oil and transmission fluid are not interchangeable. If it is transmission fluid, note that there is more than one type of fluid. It is important to identify, and use, the correct lubricant!
The transmission has a separate oil sump from the engine
The transmission will have a dipstick similar to the engine. This may be screwed in place. If so, the oil level is generally checked with the dipstick unscrewed but not always: check the manual.
The transmission oil change interval will be in the engine manual. The oil is frequently changed by unscrewing the dipstick, inserting a hose through the hole, and sucking the oil out.
There are no combustion processes within the transmission and as such the oil or transmission fluid, whatever it is, should look more-or-less the same as new fluid when it is changed, although it may darken slightly over time.
If there is emulsification, there is water in the oil. In the old days with wooden boats, wet bilges, and leather output shaft seals, the water commonly came from the bilges through the transmission’s output seal. Nowadays, it almost always comes from a failed transmission cooler (see this lesson). These are found on some transmissions and not on others.
If the oil is black, the transmission is most likely slipping and burning up the clutch plates. We will address this in the lesson on transmission maintenance.
Some transmissions have a magnet on the drain plug. If the plug is accessible and can be removed, it should be inspected for metal particles. An accumulation of particles indicates excessive gear wear.
Summary
Oil system maintenance is not difficult, especially if the engine is fitted with an oil change pump, the oil filter is accessible, and the right tools are on hand for changing filters. The key things are to have an adequate supply of appropriate replacement oil and to use oil filters from the engine manufacturer.
For most of us the oil and filter do not need to be changed more than once a year. Once it is learned, the process takes no more than an hour. Failure to carry out this basic maintenance can lead to extremely expensive catastrophic damage. It is something that should not be neglected!
Would you put a magnet on the oil filter? I have one on my Chevy.
Christian,
We sometimes find magnets on the drain plug but since these are generally inaccessible in boats this is not much use! The magnet is there to collect metal flakes as a means of warning of substantial mechanical wear/damage. If you keep up with the oil and filter changes and other maintenance you will not get this.
Nigel
Is there any risk of contamination if you use the same pump for engine oil and transmission fluid? Should you do anything to flush the pump before switching between them?
Stan,
In practical terms, ‘no’, even if the engine uses engine oil and the transmission uses transmission fluid. If the engine or transmission is pumped dry, we are talking very small amounts of potential cross contamination when you switch an oil change pump from ‘extract’ to ‘fill’.
The one time you need to be careful is if taking an oil sample to send to a lab, in which case if this is done part way through an oil change the system will be well flushed.
Nigel
My Yanmar 1988 4JHE calls to change the oil filter at every other oil change. Since I cruise full time, I change the oil several times a year (every 150hrs). Given my situation do you see much risk in following the manufacturers recommendation or is it false economy?
James,
We have to assume Yanmar has figured these things out, so go ahead and follow the recommendation. The 150 hours is, in any case, a fairly short oil change interval for many of today’s small diesel engines. My Volvo-Penta has a recommended change interval of 500 hours so if we both follow the respective recommendations you will still be changing your oil filter more often than I will be!
Nigel
It was interesting to hear that you should fill the oil up to the top mark on the dipstick. I had been told that you want to be in between the lines as the oil will expand with heating. If filled to the max and then the oil expands it could then be “over full” and possibly damage the engine. Is there anything to that or was I just misinformed?
Colin,
I have never heard this! I doubt very much that the expansion with heat makes much difference and if we don’t use the the top mark to determine the maximum fill level how are we to determine this and what is the point of it?
We definitely do not want to overfill, and there is no harm in being between the marks. Filling to a little below the top mark will ensure we do not overfill but if you end up at the top mark this is fine. The more oil you have, so long as the engine is not overfilled, the less work it will do and the better the heat dissipation.
Nigel
Hi Nigel & Jan
Thank you for your excellent On-line tutorial. It has made me more confident with maintenance issues.
I have a rather old but trustworthy Fiat 6 cylinder diesel engine in my boat (emma-sailing.ch). The newer models are named IVECO aifo 8061. Unfortunately I have not been able to find a manual for this engine.
It looks to me like the injection pump has an orifice for oil change. I plan to check this and replace the oil if necessary, as I am quite sure, that this has not been done in quite a while. Is the oil used in the injection pump the same as the engine oil?
Hi Walter,
You have a beautiful boat! 🙂 I am not familiar with your engine type, but this here seem to be its operating and workshop manual:
https://de.scribd.com/document/657589402/iveco-8061m12
https://issuu.com/engineparts2/docs/iveco_8061_engine_workshop_manual_fiat_aifo_8061
Maybe you find some details in there?
Fair winds,
Jan
Thank you very much Jan
scribd seems to be a good source for old manuals. They even had the original (in Italian) for my Fiat aifo 806. And yes, the injection pump also requires an oil change, same a type as is used for the engine.
Is it normal for the engine to consume some oil over time or does that indicate a problem? How much is too much oil consumption? On my engines I often have to add a quart or two between oil changes.
Marshall,
If that is a newer engine that is an excessive amount of oil consumption. But then we have many diesel engines in boats that are decades old, and with a considerable amount of cylinder and other wear, that still fire up and run. As an engine ages and wear increases oil consumption will very, very slowly creep up. The other thing we get on lightly loaded older engines is a considerable amount of carbon formation which gums piston rings in their seats allowing more oil into the cylinders. And we can get oil into the cylinders one or two other ways, mostly associated with older engines and significant engine wear.
So I would say the answer to your question depends on how old the engine is, how well worn, and what kind of a duty cycle it has seen. And, of course, whether or not it has any oil leaks (which most often are through the crankshaft seals at either end of the crankshaft, or a leaking gasket on the pan or the valve cover). But any way you look at it, that is getting to be quite a bit of oil consumption! But if it is an older engine with a substantial amount of wear on it that otherwise runs fine, it is likely not worth trying to fix it.
Nigel
When I run my boat’s very trustworthy, albeit old, engine, I notice a very slight oil sheen on the water. It has always been that way, since I bought the boat. There is no recognizable oil consumption, neither in the engine nor in the hydraulic transmission. There are also no signs of water in the oil, which could explain an unchanged oil level.
I am wondering where the oil in the water cooled exhaust could come from.
Could it come from the salt water cooling circuit?
As I unscrewed the lid of the saltwater pump on a recent impeller change, I also noted tiny amounts of oil in the water that I caught from under the loosened pump cover.
The impeller sits on an axle that is driven by a cog wheel in the engine. Could a weak seal between the salt water pump and the engine block be the culprit?
Are there any other suspects that come to mind?
Could it be diesel oil?
Walter,
First, the gear driven raw water pump. There will be oil seals on the engine side and water seals on the raw water side with a space between the two. Normally there is a weep hole in this space out of which any leaking oil or water will drip. In which case there is no way the pump should be a source of the sheen.
If you have a raw water cooled oil cooler (I am guessing you don’t!) a miniscule corrosion hole in one of the tubes could let very small amounts of oil enter the raw water because the oil side will likely be at a higher pressure than the raw water side.
If you have a leaking exhaust valve stem you could get small amounts of oil mixing with the exhaust gases and the injected raw water. I am thinking this may be a possibility although typically the oil gets burned off by the hot exhaust gases.
If you have a hydraulic transmission it likely has a raw water cooled oil cooler so corrosion here could also be a source of oil. This is more likely!
Other than that, there are no points of contact between the oil side of the engine and the raw water side.
This could also be a diesel sheen from a failing injector. Are you sure all cylinders are firing as they should?
Nigel
Thank you, Nigel
Indeed, the seawater pump has a weep hole between the engine and the pump. A little oil and water collects in a drip tray.
Thanks for the tip about the seawater-cooled oil cooler of the hydraulic gearbox. I will check that next.
Cheers
Walter
My new-to-me boat has a powered oil change pump installed, which is great! How worried should I be about failure of that pump? I’d love to save the space and not cruise with an extra manual pump, but if the powered pump goes out, what kit should I have on the boat to get oil out?
Adam,
If the oil change pump has been professionally installed it should have a very rugged hose connection to the crankcase. Something that needs occasional inspection (maybe at an annual haul out) but nothing to worry about unless it starts to show obvious signs of deterioration (e.g., a drip) in which case it needs immediate attention.
Our preferred manual pump is the vacuum type with a large enough waste oil containment capability to do a complete oil change, but you are correct, this is quite a large piece of kit. The other way to go is to have a stand-alone pump (which is typically a plunger-type pump) with the discharge hose fed to a suitable empty container (for example, the oil can which contained the oil for the previous oil change). You still need to store the empty containers, but now you are dealing with several smaller containers which are much easier to squirrel away somewhere.
The pump and its associated hoses will inevitably drip a little waste oil after use so have a large enough heavy-duty resealable bag to contain the coiled-up hoses and the pump.
Nigel