Recommended lower unit lube 1994 C25 Yamaha 25 hp

[jspriddy]

I've just bought a 1994 C25 Yamaha and want to change the lower unit oil. I don't have a manual. What oil is recommended by Yamaha? Other recommendations would be appreciated.

Is there any reason to flush the old oil with a solvent, or should I even consider that?

Also, could synthetic be used in this engine?

I did several searches and did not find a definitive answer in the forums, or on the web.

Thanks, John

 

[Sea Rider]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

Just any high quality gear oil, could be 90 monograde, or 80/90 multigrade, you lower unit needs about 300 Ml. Place a pan under leg, remove both oil plugs, let all used oil out, squirt a generous amount of new oil in upper plug hole while turning prop with hand, let all new oil out. Fill with new oil from lower plug untill you see oil comming from upper plug. Tight upper plug first, remove bottle's neck, then lower. No need to flush gear case with any solvent. Used oil must not be milky color, if so, lower seals are worn and must be replaced with a LU kit.

Happy Boating

 

[99yam40]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

Only time I fool with flushing is if there was water found in the unit just to be sure I removed all I can, and even then it is not with a solvent. Maybe some thinner oil and then drain well before filling again. Any marine grade lower unit oil from any marine or big box store is fine

 

[jspriddy]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

That's what I was looking for. Thanks, both of you. You read all this stuff about racing teams, and blah, blah,...it seems long on theory and short on practical usage.

Again, thanks.

John

 

[Sea Rider]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

Don't use any type of solvent, you have rubber seals, o'rings inside LU. Just drain well all used oil and replace with new each 100 working hours. There is no such marine grade oil, all are 80-90 gear oil sold on marine cans, this issue has been widely discussed. As an example have used 80/90 Chevron standard gear oil for more than 14 years in all my Evis, Yams and Tootsies, none has suffered gear related issues for using a "non marine grade oil" As we don't know when was the last time previous owner changed tail oil, a small flush with new oil won't do any harm...

Happy Boating

 

[jspriddy]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

...There is no such marine grade oil, all are 80-90 gear oil sold on marine cans, this issue has been widely discussed. As an example have used 80/90 Chevron...

You're kidding!!! No, really, I wondered why any good gear oil would not work. I have 80w90 in bulk in my shop (small tire business). I may flush with it and then fill with the over-priced, over-packaged stuff I bought tonight. Oh well, live and learn. By the way, I figured out "Evis" and "Yams", but what's a "Tootsie"?

John

 

[DanMC]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

All the above tips are good,but i don't think i read anyone recomending synthetic...that's what i would make sure goes in our motors (2010 Honda BF2 and 2011 Honda BF25)... ,engine and lower leg/unit...and your motor will last and last.
Dan

 

[99yam40]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

I always thought that the marine grade had something to do with the lower units being run under water and salt water a lot of the time and normal automotive type gear boxes are not run under water and not sealed units. The additives should be different. But I have never actually looked into it.
It has always been just convenient to purchase the one with the nozzle that fits the lower unit drain hole to get it into there.

The main thing is to change often and make sure no water/moisture sits in there for any length of time on the bearings and gears.
Using overpriced synthetic just seems like overkill if you change it often

 

[Sea Rider]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

By grade you mean the viscosity of a given oil, definitely is not 30-40-20/50 engine oil, is much viscous, between 70 to 90, could be monograde or multigrade, gear oil works inside lower leg perfectly sealed, so if water, moisture whatever is not inside will run and lube perfect. It evens turn milky when lower seals are worn, just change every 100 worked hours and you'll be fine. Tootsies are Tohatsu's

Happy Boating

 

[99yam40]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

no by marine grade I was meaning the different additives in the gear oil for marine service.

 

[jspriddy]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

"Tohatsu"?? That's a new one for me.

80w90 is a fairly common automotive gear lube, considering that there are not many passenger cars around with rear differential any longer. Some RWD vehicles use synthetics. You have to be careful what you put in them, now. We used to use a lot of ??W140, but don't see that much anymore.

Thanks to you all for your replies. I've bought some QS gear oil and intend to change often.

John

 

[Sea Rider]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

It's virtually impossible to know which aditives gear oil uses, but assume outboard brands sells multigrade bottled gear oil so to work well in wordwide different heat/cold water environments. 140 is used on heavy gear cases, not for outboards though. Sae 80/90 is used in most of the front wheel drive vehicles, not only on rear drive ones. Place a Tiny Tach or Hardline hour meter inside engine cowl and change gear oil every 100 worked hours.

Happy Boating

 

[jspriddy]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

It's virtually impossible to know which aditives gear oil uses, but assume outboard brands sells multigrade bottled gear oil so to work well in wordwide different heat/cold water environments. 140 is used on heavy gear cases, not for outboards though. Sae 80/90 is used in most of the front wheel drive vehicles, not only on rear drive ones. Place a Tiny Tach or Hardline hour meter inside engine cowl and change gear oil every 100 worked hours.

Happy Boating

Most FWD vehicles are automatic, so they use transmission fluid-Mercon, Dextron, etc. A lot of light manual transmissions use auto fluid, as well as motor oil, such as 30w, etc.

I don't intend to put automotive grade in my motor. Marine grade is not that expensive, motors are. At least for me.

Thanks,

John

 

[robert graham]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

Walmart sells a quart of Marine Lower Unit Oil for about $4, with the specified additives for water/marine applications, so why wouldn't you use it?...to save maybe $1 on oil?

 

[jspriddy]

Re: Recommended lower unit lube 1994 C25 Yamaha 25 hp

Walmart sells a quart of Marine Lower Unit Oil for about $4, with the specified additives for water/marine applications, so why wouldn't you use it?...to save maybe $1 on oil?

Yeah, that's what I thought. But the Quicksilver brand was about $11. But that's still cheaper than a lower unit rebuild. As I said above I don't intend to put automotive grade in my motor.

John