Does motor oil go bad if left in the pan for more than a season?

[2550SX]

I was performing some maintenance on the boat I picked up last winter and I could not recall if the previous owner said he changed the engine oil prior to selling it to me. It looked clean but I thought better to change. It is a 1992 Mercruiser 454 OD717696 which I found out takes 7 quarts. Mercruiser Manual 16 said straight 40 weight for ambient temperatures over 50F. Change every 100 hours of use or once a season. I've heard good things about full synthetic and use in my cars but the only synthetic 40 weight I could find on-line was Royal Purple. I wasn't sure which filter to get so I bought a AC Delco PF454 because the engine is a 454. Makes sense right?

My question is, if I am not going to get anywhere close to 100 of use this season as it is already August (Thanks COVID) is it still better to change every season?

I am unsure why oil would go bad if left in the pan more than a year and would like to understand why.

Even though the oil I bought wasn't cheap and I am not excited to dump it after only 10-20 hours of use annually the greater deterrent is that its sort of a pain in the ***** to change. So if dumping premium oil after minimal use is best for the engine I will surely do it. I just don't understand the risk in waiting closer to the recommended 100 hours despite how long it takes to get to that point.

I am curious to hear what other mercruiser owners suggest. Your insight is greatly appreciated.

End of ever single season regardless of use? Or every 100 hours whenever that is?

 

[Scott Danforth]

if you never started it, the oil will be fine.

if you have started it and there is any moisture and combustion by-products, the oil becomes acidic and starts to eat the bearings when it sits.

so, if you use the boat at all (for 1 hours or 50 hours), you must change the oil. yes, that is every 100 hours or every year, which ever occurs first. todays manuals call for every 50 hours.

 

[H20Rat]

I've seen MANY boats in the last 30 or so years that got an oil change every other year. Never once have seen an I/O engine an oil related engine failure.

In the classic car world, it isn't uncommon for a car to sit 6 months at a time. Those guys don't do an oil change every time they park it. I haven't changed oil on my RV (big block Ford 460) in 6 years. I don't put many miles on it, and the 460 rope seal tends to leak out fast enough that it is sort of self changing!

Not recommending that for everyone, but your engine won't immediately die if you don't change it.

 

[Furbird]

My suggestion would be doing whatever is needed to make the oil not a pain in the hind quarters to change. Mine has the hose that you can pull out the drain plug hole and the threaded dipstick tube for doing a suction change. I use the drain hose personally. If you have a bottom mount filter, get a filter relocation kit. Whatever is making your life difficult, invest the money to make it easier.

Also, I own multiple vehicles, they all have synthetic, and they all get changed annually because I never put enough miles on any one car to hit any oil change interval no matter how short it is. I believe there was one period of time where I had put less than 100 miles on one of my cars over the course of 4 years but it had it's 4 oil changes. It's just not worth it to me to put it off.

 

[Searay205]

First oil change on a boat that is over 30 years old and well over a 1000 hours and still running was when it was 6 years old. The oil filter rusted through. After that I chang oil every 3 years. Never once had any engine failure do to lubrication break down. I knew a guy worked for Mobil back in the 90's. He never changed his oil in 150K miles. He would change filter once a year and top off oil level. There was a commercial once in the 80's where Mobil advertised the last oil change you will do. He gets a call guy engine locked up after 80K miles. Nothing in pan but metal. Guy didn't read the small print to keep a level of oil in engine. Mobil didn't pay out not because they couldn't afford they didn't want to set a precedent.

 

[Rick Stephens]

The issue with boat motor oils is the formation of Sulphur Dioxide, Nitrous Oxides, and Carbon Dioxide. Add a little water, not much needed, just high humidity as an example, and all of those gases form Sulphuric, Nitric and Carbonic acids as all three oxides dissolve readily in water. Most of that blows out the exhaust. Some always contaminates the engine oil. More so in boats than cars and trucks since water is almost always present in small amounts in the fuel system. Hence the warning that running a motor and parking it can pit your bearings and cylinder walls. Personally, I think the acid damage is present and no different even when I am using my boat for 5 hours a week. I change the oil every year in both inboard and outboard engines. Too cheap and makes me feel good to park it with clean oil.

Also know that fresh oil left in a plastic bottle tends to suck up H2O, nitrogen and hydrogen through the plastic and degrades over time even in a sealed bottle. Old oil is probably nearly as dangerous as used oil. I doubt using either is very hazardous to engine life.

 

[achris]

... its sort of a pain in the ***** to change....

You're aware the dipstick tube goes all the way to the bottom of the sump? You can get a pump to suck the oil out...

Chris....

 

[JASinIL2006]

I have changed my oil every year religiously except last year when we only were able to use the boat for a 2-week period, maybe 10-15 hours max and I had hand surgery in early September that prevented me from doing any mechanical work. I figured with only a few hours, the oil and gear lube wouldn't have seen enough wear or contaminants to cause serious problems. I don't intend to repeat that, though, and my oil will again be changed every fall when I put the boat to bed for winter.

I figure that, between the high revs a boat sees for extended periods of time, plus the fact that an engine conking out on the water is so inconvenient (and potentially dangerous), I'll do whatever I can to take care of it. My vote would be to change it even if you don't get close to 100 hours.

 

[Searay205]

I will attest the Topsider vacuum extractor works flawlessly!!! And it will get all the oil out but maybe a 1/2 teaspoon. Very impressed and so much easier than crawling under engine and draining into bilge out drain plug hole. Then you have a can of used oil and tubing dripping oil all over the place then you have to store blah blah blah

 

[chs marine service]

as for the oil, regasrding the 5w or 10w or 20w on the oil bottle, ie 10w40
the w stands for winter, not weight
this means in the winter, the oil acts like 10 weight and in the summer acts like 40. so it does not matter which grade oil you use as long as the last # is 40.. becaus youare not using your boat in the winter.

i use castrol 10w40 synthetic.. also synthetic oil is notchanged as often as traditional.

In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the "W" number the better the oil's cold temperature/cold start performance. [h=3]Oil Specifications Explained - What does 10w40 mean?[/h] www.driverstechnology.co.uk › oils

 

[2550SX]

Thanks for the feedback. There is a lot of knowledge here.

 

[cchamp]

as for the oil, regasrding the 5w or 10w or 20w on the oil bottle, ie 10w40
the w stands for winter, not weight
this means in the winter, the oil acts like 10 weight and in the summer acts like 40. so it does not matter which grade oil you use as long as the last # is 40.. becaus youare not using your boat in the winter.

i use castrol 10w40 synthetic.. also synthetic oil is notchanged as often as traditional.

In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the "W" number the better the oil's cold temperature/cold start performance. [h=3]Oil Specifications Explained - What does 10w40 mean?[/h] www.driverstechnology.co.uk › oils

What is considered a low temperature?

 

[JASinIL2006]

I use whatever weight Mercruiser specifies for my engine. Dino oil, synthethic, or a blend is up to you.

 

[indybleck]

Might want to make sure you have the right filter

 

[MI CC]

if you never started it, the oil will be fine.

if you have started it and there is any moisture and combustion by-products, the oil becomes acidic and starts to eat the bearings when it sits.

so, if you use the boat at all (for 1 hours or 50 hours), you must change the oil. yes, that is every 100 hours or every year, which ever occurs first. todays manuals call for every 50 hours.

So if I change the oil at the end of the season and then drive the boat a 1/2 hour to the hoist, that's not good to have sitting all winter?

 

[chs marine service]

What is considered a low temperature?

winter weather. not boating weather unless you are a charterfisherman or something like that.

 

[achris]

So if I change the oil at the end of the season and then drive the boat a 1/2 hour to the hoist, that's not good to have sitting all winter?

One of the byproducts of combustion are sulphites. Another byproduct is water vapour. Some of those will pass the piston rings and end up in the oil. When sulphites and water combine they form sulphuric acid. Sulphuric acid eats crankshaft bearings. You want that sitting in the engine all winter? So yes, even driving 1/2 hour to a hoist 'contaminates' new oil.

winter weather. not boating weather unless you are a charterfisherman or something like that.

Winter here produces some of the best boating weather.

Chris...

 

[Scott Danforth]

So if I change the oil at the end of the season and then drive the boat a 1/2 hour to the hoist, that's not good to have sitting all winter?

nope, not good.

here is a pic published in engine builder magazine (sourced from Clevite) of acid degradation of a bearing

since babbitt bearings are made from soft alloys, they are easily attacked from the acid buildup in the oil.

ever wonder why many people have boat motors "with only 50 hours" or "with only 120 hours" and have knocking rods or mains........ its from lack of annual maintenance, including oil changes.

in your case, change the oil on the hoist

 

[JayhawkCurtis]

Im not saying you are not correct Scott, but unless you run your motor after you change the oil, you have new oil in the pan, and used contaminated oil still in the bearings. So if you run your engine to get fresh oil to the bearings, you have contaminated the oil, and it needs to be changed again.
I guess just crank the motor to get fresh oil to the bearings?

 

[Scott Danforth]

or boat all year