Oil Type

[KrisA]

What oil are most you running in the Merc 502?

We have a 1998 252 and want to make sure we run the best oil possible. Manual says Quicksilver 25w40 and specifies to not use synthetic.

[cmattj]

That’s a great oil and a great viscosity for that era 502.
As you may see “ blends “ of synthetic with petroleum that will be fine as well.

A lot of things have changed along the way but stay with a mfg recommended oil weight.
Your hot idling oil pressure will be the best.

[jhnmdahl]

Matt, this sounds like a great application for Mobil 1 15w-50, no? I know a lot of people have switched to a heavier synthetic with these, which tend to use a bit of oil and have somewhat looser tolerances than a lot of newer engines. Shell Rotella 15s-40 seems to be popular as well, and may be cheaper if your local Walmart doesn't have the 5 quart jugs of Mobil 1.

[cmattj]

Matt, this sounds like a great application for Mobil 1 15w-50, no? I know a lot of people have switched to a heavier synthetic with these, which tend to use a bit of oil and have somewhat looser tolerances than a lot of newer engines. Shell Rotella 15s-40 seems to be popular as well, and may be cheaper if your local Walmart doesn't have the 5 quart jugs of Mobil 1.

You bet.

As API specs change every year you can be insured to get a usable full synthetic like Mobil 1. I may add that the Rotella 15w-40w you mention is a very good replacement in a petroleum based oil, as it contains properties that work well in the Marine engine world. ( The newer platforms may require less viscosity )

The control of moisture, and oxidation are a plus with that oil.

Not just for diesels anymore!

[AsLan7]

Matt, this sounds like a great application for Mobil 1 15w-50, no? I know a lot of people have switched to a heavier synthetic with these, which tend to use a bit of oil and have somewhat looser tolerances than a lot of newer engines. Shell Rotella 15s-40 seems to be popular as well, and may be cheaper if your local Walmart doesn't have the 5 quart jugs of Mobil 1.

You bet.

As API specs change every year you can be insured to get a usable full synthetic like Mobil 1. I may add that the Rotella 15w-40w you mention is a very good replacement in a petroleum based oil, as it contains properties that work well in the Marine engine world. ( The newer platforms may require less viscosity )

The control of moisture, and oxidation are a plus with that oil.

Not just for diesels anymore!

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Great advice gents.

To piggyback with ya’, much has changed in oil technology since the printing of the 22 year old, 1998 502 Merc manual suggesting to “avoid Synthetic oil”in the engine that KrisA owns. Those were the end of the crossover years changing from flat tappets to roller tappets in the 502. Zinc additive in oil that helped those components operate with minimum wear was diminishing under EPA regulations as synthetic oils came onto the consumer market. Merc couldn’t recommend these synthetics initially. (I’m sure Merc marketing and pocketbook played a role in this too...as it does now. )

Fast forward to 2020 and the American Petroleum Institute (API) ratings have evolved from the original SA category for engines built before 1930 to an API of SJ during KrisA’s pre 2000 engine marque ...to the present SP category for 2020 engines.
(See chart and select gasoline tab).

Certain automotive oils can now work in these marinized automotive engines designed for constant high RPM loads and marine environments. Of course you can never go wrong with the manufacturer’s recommended oil—especially under warranty. Mercury (and Quicksilver) 25W-40 regular and now semi-synthetic blend will work for ALL their 4 stroke sterndrive engines including the catalytic models as per Merc’s latest recommendations located on the Merc recommended Oil website.

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That being said, other high quality oils like Mobil 1 15W-50 full synthetic with its increased Zinc content (1300 ppm) will work fine as this meets or exceeds all the API specifications that have evolved throughout the years as shown on the Exxon Mobil website. Again this product has the necessary additives such as (flat tappet lubricating Zinc) for older generation engines.

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I personally run full synthetic in every machine we own due to its superior cylinder wall coating ability between engine use (which also helps in corrosion resistance) and superior breakdown properties under stress.

Honestly though, you’ll find with all this discussion about oil, other than racing applications, it’s rare to find an engine fail due to the type of oil being used. Other components of the boat normally fail first...or in our case with cars in the north east, rust away before the engine ever fails.

Hope this helps a little KrisA. Probably more than you wanted to know but it’s what we do here.

Cheers.

[akorcovelos]

Yeah, at the core it’s just important to make sure there IS oil in the engine, lol. I used to use Delo 400 diesel oil in my old Merc 260 because it spent most of its 3000 hours lugging just off plane for wakeboarding. Now I run the Quicksilver 15/40 as I mostly cruise and run higher rpms in the Cobalt. As AsLan said, modern oils have narrowed the gap in what works and what doesn’t based on engine age.

[KrisA]

Thanks everyone. I run full synthetic in every other vehicle we have too. Just didn’t want to mess something up in this big block.

[Big Block Power]

I'm a run with factory stuff guy. Semi syn merc 25w40.
I still believe they put special additives in the oil for marine applications.

[AsLan7]

I'm a run with factory stuff guy. Semi syn merc 25w40.
I still believe they put special additives in the oil for marine applications.

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That’s kind of funny considering you posted the pic of the Merc factory presumably not even using their own oil at times . Wasn’t it Pennzoil or something similar? Find that pic again.

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[Big Block Power]

I'm a run with factory stuff guy. Semi syn merc 25w40.
I still believe they put special additives in the oil for marine applications.

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That’s kind of funny considering you posted the pic of the Merc factory presumably not even using their own oil at times . Wasn’t it Pennzoil or something similar? Find that pic again.

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It is factory oil see

[AsLan7]

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Ahhh yes....that's the one. Merc racing engine shop with cases of Kendall motor oil in the background. (Circumstantial evidence of course as who knows what could be in those boxes. )