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Changing the oil in my 60 HP 4 stroke Mercury. What do you use?

25W40 on my Mercury 75HP, which is what the local dealer recommends. But you can use 10W30 as well if you will be using your motor at lower outside temperature.
From Mercury:
Engine Oil Recommendations
We recommend the use of Mercury or Quicksilver SAE 10W-30 multi-viscosity 4-Stroke Outboard Oil for general,
all-temperature use. If SAE 25W-40 multi-viscosity oil is preferred, use Mercury MerCruiser 4-cycle engine oil or
Quicksilver sterndrive & inboard 4-cycle engine oil. Never use 4-cycle engine oil that is not certified to meet or
exceed any one or combination of the following American Petroleum Institute (API) Service Classification SH, SG,
SF, CF-4, CE, CD, CDII. Severe engine damage may result from use of an inferior oil.

Does anyone know why you cannot use 10W40 oil?

25W40 is thicker in when motor is cold. Whats the benefit of that?

You can use 10W40 if you want. Perfect for colder climates.

Do you use Mercury's or Quicksilver Oil or do use an oil available for use in cars?

Just use what's recommended by the maker of the motor. They built the thing. Only use oil specifically designed for marine motors. They have special additives in them that you will not find in other oils. The single best investment for ANY combustion engines you will ever make is oil. Never go cheap if you can afford it.
I've been working on engines from lawn mowers to Cf-18 jet engines with virtually anything in between. (i've had a weird life...)

I have a 70 Yamaha and a 9.9 Merc on my Mac. I have a 50 Yamaha and 6 Tohatsu on my duckboat. All are 4-strokes. I use synthetic (MobileOne) 10-30W. Meets or exceeds all manufacter's specs.

mallardjusted wrote:I have a 70 Yamaha and a 9.9 Merc on my Mac. I have a 50 Yamaha and 6 Tohatsu on my duckboat. All are 4-strokes. I use synthetic (MobileOne) 10-30W. Meets or exceeds all manufacter's specs.

I am a big fan of synthetic lubricants (wink-wink), and nothing but AMSOIL goes into my Amphicar if I can help it, in particular their water-resistant grease, which has kept my amphibian clown car's wheel bearings, suspension bits and other water-dunked mechanisms quite happy indeed for over two decades. In fact, in a kind of reverse Hair Care Club for Men move, back in the day I even became an AMSOIL dealer, and the small referral proceeds earned thereby from me and other Amphicar-owning folks using my AMSOIL Dealer Number 508472 when purchasing their slippery goodies (which didn't cost a nickel more to do), helped pay the server rental for the website Amphicar.net. Pretty much mothballed now on the free-hosting service 000webhost.com, the site's still out there as a relic from the dawn of the World Wide Web, still partyin' like it's 1999--though it's nevertheless still pretty damned useful for owners as a repository for lots of technical stuff we "web-toed motorists" need. It was basically intended as the International Amphicar Owners Club's "Slutty Sister Site", where basically any owner with a keyboard and screechy modem could have their way with her, bang together a nice little website, have an @amphicar.net email account, host their images...That sort of thing. Its old AMSOIL for Amphicars catalog page is still there (and may be worth visiting, if only to gaze upon the utterly bodacious "Miss Luberack" of the Eisenhower Era in all her glory surrounded by glassy-eyed slick-haired grease monkey admirers), and while some of the AMSOIL products described in it have long been updated or superceded by newer products, I believe their water resistant grease is still just as it always was: perfect. Based on my long and happy experience with it, I will also put nothing else into my two boat trailers' bearings. If you want to try that grease, I believe you can still use that Dealer Number 508472 when ordering.

As for my Honda 2001 BF50A outboard, which some of you may recall had that "making oil" issue described here--and which I hope I've since squared away with a new thermostat--Based on my rummagings through this and other forums, like this one, for the time being at least she presently has a belly full of Castrol GTX High Mileage 10W-30 Synthetic Blend, which was just $17.47 for 5 quarts at Wallyworld. Apparently, although neither Honda nor the engine's manual recommend any specific brand of oil, or even their own Honda brand, (Page 64 of the manual's "Engine Oil Recommendations" simply reads, "Oil is a major factor affecting performance and service life. Use 4-stroke automotive detergent oil. SAE 10W-30 is recommended for general use. The SAE oil viscosity and service classification are in the API label on the oil container. Honda recommends that you use API SERVICE category SG or SH oil with the ‘‘starburst’’ certification mark displayed on the container). With said, I am led to understand that Honda used to specifically recommend Castrol. So, that's how I am going for now, along with just a dash of Marvel Mystery Oil (maybe 3 or 4 ounces) in the crankcase, until I am sure that whole "making oil" thing is history. Despite warnings in some forums not to, I may well go full synthetic like AMSOIL or maybe Mobil1 at some point. But, since I am likely to be draining my oil a couple-few times just this coming season anyhow as a sort of Marvel Mystery Oil-assisted ongoing gentle engine flush for a motor that must have sat for at least a decade before I got her into the drink last year, going costly full synthetic might be overdoing it just a tad, yes?

As for the other fluids in the outboard, I am using the Honda brand Power Trim and Tilt Fluid in the trim hydraulics, while for now the lower unit is full of Wallyworld's house brand Super Tech 80W-90 Marine Gear Lube, which is the required GL-5 grade (actually, the manual states "GL-4/5"). Again, once I've flushed her lower drive unit a couple-few times, and used up what I have, I will almost certainly change to this AMSOIL Marine Gear Lube, which is a combination GL-4 or GL-5, slightly different than the straight GL-4 I like to use in the Amphicar's early '60s tranny (since some makers' GL-5 oils' phosphorous-based anti-impact additives to bring them up to that GL-5 rating can chemically degrade the Amphicar's old-fashioned brass synchronizer doodads). Last I checked with their tech folks, AMSOIL didn't use phosphorous-based additives in any of their their gear lubes, but still... As for your Honda's modern outboard drive, GL-4 or GL-5: it just won't matter much. The main thing is to change it frequently--like at least once a season, which is super-easy to do, and to make sure what comes out is not "milky" and/or "frothy" like a milkshake from water ingress mixing with the oil. If it is (and thankfully mine was not), then you would do well to replace some seals and whatnot in there that are letting that water seep in. If you're a true novice mechanically speaking, then you might want to just let a professional marine mechanic handle that for you. It might be a good time to replace that water pump impeller as well. Figure on spending a couple-few hundred bucks, depending.

Bilgemaster wrote:The main thing is to change it frequently--like at least once a season, which is super-easy to do, and to make sure what comes out is not "milky" and/or "frothy" like a milkshake from water ingress mixing with the oil. If it is (and thankfully mine was not), then you would do well to replace some seals and whatnot in there that are letting that water seep in. If you're a true novice mechanically speaking, then you might want to just let a professional marine mechanic handle that for you.

Those bottom seals, behind the prop, are not for the faint of heart. And in the Honda at least, that bearing housing is probably not coming out without a fight (and something breaking) if it's old like mine.

Tomfoolery wrote:

Bilgemaster wrote:The main thing is to change it frequently--like at least once a season, which is super-easy to do, and to make sure what comes out is not "milky" and/or "frothy" like a milkshake from water ingress mixing with the oil. If it is (and thankfully mine was not), then you would do well to replace some seals and whatnot in there that are letting that water seep in. If you're a true novice mechanically speaking, then you might want to just let a professional marine mechanic handle that for you.

Those bottom seals, behind the prop, are not for the faint of heart. And in the Honda at least, that bearing housing is probably not coming out without a fight (and something breaking) if it's old like mine.

You can always do what I did, being only a "semi-novice" engine mechanic. Remove the Lower Unit. Remove the prop. Deliver the LU to a Honda dealer and let a mechanic with the tools and the knowledge do the hard part and replace the seals. I think I only paid $175 or so in labor. You can opt to have them replace the impeller while the LU of off, or replace the impeller yourself when you get the LU back. Be sure to change the O-ring under the Impeller housing too. Even after a new seal replacement I still found some water seepage (but much less than before the new seals) and traced it to that O-ring. After replacing the O-ring it stopped completely.

paul I wrote:

Tomfoolery wrote:

Bilgemaster wrote:The main thing is to change it frequently--like at least once a season, which is super-easy to do, and to make sure what comes out is not "milky" and/or "frothy" like a milkshake from water ingress mixing with the oil. If it is (and thankfully mine was not), then you would do well to replace some seals and whatnot in there that are letting that water seep in. If you're a true novice mechanically speaking, then you might want to just let a professional marine mechanic handle that for you.

Those bottom seals, behind the prop, are not for the faint of heart. And in the Honda at least, that bearing housing is probably not coming out without a fight (and something breaking) if it's old like mine.

You can always do what I did, being only a "semi-novice" engine mechanic. Remove the Lower Unit. Remove the prop. Deliver the LU to a Honda dealer and let a mechanic with the tools and the knowledge do the hard part and replace the seals. I think I only paid $175 or so in labor. You can opt to have them replace the impeller while the LU of off, or replace the impeller yourself when you get the LU back. Be sure to change the O-ring under the Impeller housing too. Even after a new seal replacement I still found some water seepage (but much less than before the new seals) and traced it to that O-ring. After replacing the O-ring it stopped completely.

When I was researching water ingress into the LU, there were a lot of stories about folks breaking something trying to get the bearing carrier out. That big aluminium nut doesn't want to come off. Some folks have even broken the LU housing. But I believe it is possible to get the seals out without taking that carrier out of the LU housing by driving in a screw and then yanking it out. Twice, as there's two in there, one facing each way.