Need help on a couple 25hp mercs

[boater1234]

I have 2 25hp 2 stroke mercs. I have a 1993 and a 2002,they are both in pristine mint condition.I am pulled more towards the 93 i have because i love the way it looks and i like the older tiller style and the cowling style better,Plus i believe from running both the 93 is faster,other than that they are the same.

QUESTION 1 The biggest difference i have been reading about is the 93 has a Nikasil powerhead and the 02 has a Mercosil powerhead.Can someone please explain which is the better powerhead because i'm having a tough time on which one i want.The 93 has 25 hrs on it and the 02 has 4 hrs on it but i'm just drawn to the 93 more.I know the basics on the mercosil vs nakisil debate and that most people think that the mercosil was the worst thing to happen to merc but i have also read some good things.I have mostly read that the nakisil powerhead is as bulletproof as they come,i can use any facts or help on this it would be great.

QUESTION 2 I have been reading about the exhaust manifold cover being changed every yr and some people say to never mess with that gasket unless leaking. Does anyone actually change that outside or both gaskets on the manifold ever?????Most people say to just leave it alone as neither is leaking and can lead to broken bolts which i def don't want again.Any help on this issue would be great,thanks.

 

[boater1234]

No help on this I presume, anyone??????

 

[flyingscott]

Both blocks are Mercosil. They are essentially the same motor. I change the exhaust gaskets every 3 yrs. Most important the waterpump needs to be changed regularly those blocks do not take overheating at all.

 

[boater1234]

The 93 is not mercosil,they started making them in 94,I called merc,they said if it has the upside down mercosil stamp then it's a mercosil powerhead,the 93 is a nikasil powerhead. The only thing that scares me is the bolts breaking off on the manifold gasket cover. All the other bolts I have taken apart so far, (lower unit bolts and thermostat bolts )have come off like butter,very easy so I hope if I try the manifold gaskets the cover comes off easy,the bolts I should say. Now do u change both gaskets or just the outside one????

 

[boater1234]

I just did a complete water pump change on it,new housing,new plate,gaskets,washers,impeller, and key so it's all brand spanking new, lol.

 

[flyingscott]

The 93 is not mercosil,they started making them in 94,I called merc,they said if it has the upside down mercosil stamp then it's a mercosil powerhead,the 93 is a nikasil powerhead. The only thing that scares me is the bolts breaking off on the manifold gasket cover. All the other bolts I have taken apart so far, (lower unit bolts and thermostat bolts )have come off like butter,very easy so I hope if I try the manifold gaskets the cover comes off easy,the bolts I should say. Now do u change both gaskets or just the outside one????

The mercosil blocks can be bored out if something happens the chrome plated block has to be sleeved or re-chromed. I don't think you have to worry about the manifolds yet with those Hrs on it. I run mine a lot so I do it every 3 yrs but that is probably 200+ hrs on it. More of an issue after an overheat than anything. They made both blocks in 1993 I had one.

 

[boater1234]

I'm just going by what merc told me,either way I have one of each and I have seen some threads on multiple forums who say the mercosil powerhead was the worst thing merc ever did because the original nikasil powerhead has been proven to be bulletproof. I just don't want to break any bolts off on that manifold gasket cover. I see allot of people have that issue, but like I said all the other bolts so far on this outboard have come off like butter so that is a plus. The gaskets are not leaking but I guess this fall I'm going to do some work on my 93 so I guess I can change the gaskets to.

 

[boater1234]

The main thing on these mercosil powerhead is to change that manifold gasket so no water can get into cylinder #2,that plus overheating like u mentioned seemed to be the biggest issues on this particular outboard, other than that they have been bulletproof. Thank u for the info so far,if u have anymore I would love to hear it. I'm a maintenance freak when it comes to my outboard, lower unit oil changes every 6 months, impeller every couple yrs or so,I wash it down good after every saltwater trip,maintenance is the key to longevity.

 

[boater1234]

Did u have any bolt issue getting the manifold cover off and do you replace both? The gaskets themselves are not leaking or are not in bad shape at all I just figured why not because that seems to be a biggie that can cause some serious ramifications if not maintained at least every 5 to 10 yrs at the most. From other sites and this one most people don't ever mess with it ever unless it starts to leak so I guess they must hold up for most of the life of the outboard.

 

[boater1234]

So far since I bought it I did a ton of maintenance on it,I replaced both coils, wires,spark plugs, complete carb job,full water pump replace,key,washers,impeller,housing, etc...,new male fuel connector on engine,brand new full fuel assembly with new on engine filter, new gas lines,new hose from thermostat to pee hole,new thermostat and gasket,pull cord, regreased everything, new tilt pin,new lower unit oil and oil drain plugs and gaskets, etc.... I'm glad I did it all to because after sitting for over 20yrs most of the stuff was either brittle or rotted out rubber. I have only $1250 invested with all that stuff to. Next is a 25hp carb because it's actually a 20hp,a nice refreshing paint job just because I want to and new decals then she's all done.

 

[flyingscott]

You have 2 really nice motors I don't know about either one being more problematic than the other I have had both. Really the only thing that kills them is overheating they won't generally come back from that like an evinrude. I always run synthetic oil oil on those for piece of mind and my bolts came right out no problems at all.

 

[boater1234]

Ok,I love the 93 20hp merc honestly, but when I felt the power of that 25 it was just an amazing difference. Truth be told,top end is such a slim difference, we're talking like a mph or 2 at the most but the torque on take off nearly threw me off the boat with the 20hp and the 25 just was a rocket ship it has so much power. What I probably will do is keep the 20hp, buy and install a new 25hp carb on it and then put a nice fresh coat of paint on it with new 25hp decals since it will be a true 25hp mercury after the carb swap. Then that will be that as I will keep her forever. The thing I know is that the 25 hp is so tight like a new car so it will be tough to get rid of also. I mean it's cherry. The amazing part is I paid only $1000 for the 93 and only $800 for the 02 if you break down the whole package I bought,I'm going to make a hefty profit on one and keeping the other . I love the older style better imo. I like the skinny tiller handle and the sleek cowling, love it. I absolutely love these mercs,I'm love the 15hp also,bulletproof as well. Thank u for the info, means allot to me.

 

[boater1234]

I'm sorry, did u say you replace both the manifold gaskets or just the outside one???? Also I use royal purple full synthetic oil as well,I have 2 gallons of it and I have to tell u I thought it would smoke much less but that is absolutely not the case,smokes like a chimney. I may have the fuel/air mixture screw just a tad to rich so that may be causing the issue but it does idle awesome and it doesn't miss a beat from a dead stop to wot. No hesitation whatsoever. I know they run 50:1 but 16oz of oil seems like way over kill in a 6 gallon tank of gas. I'm going to cut back just a hair to see if it runs a bit better, I'm going to cut back to 65 to 75:1 and just experiment with the ratios. I don't believe with synthetic oil it will hurt to run like 11 or 12oz of oil compared to 16. First thing I will do is lean out the screw just a hair. Does your merc smoke like a chimney? Also what ratio are u using and what oil?????? Any info u can give me on your outboard and the way it runs or don't runs would only help me out more and more. This is great because we have the same outboard and since you have 10 times the running on yours that u could tell me your experiences with it if you would, I love to learn so much more about my motor if you could educate methanks for any help.

 

[flyingscott]

DO NOT run them with less oil keep it 50-1. I run amsoil injector oil mixed 50-1 all the time. Smokes like a normal 2 strk does. My current one is a 1987 model 25 hp. They are a really good running outboard I love the tiller shift. Right now mine is broke I have to get to it next week. But overall they are extremely reliable and my favorite 25 hp.

 

[boater1234]

Why do you say not to run it on anything but 50:1,actually my merc manual says 25:1 on break in then 100:1 for normal regular use which I know it can be run on that ratio because yamahas do and the engines materials are the same. I just know from reading the reasoning for the companies going back to the 50:1 oil ratio was not for any wear or tear from everyday use it was from sitting for months and months that there wasn't a good enough oil film left on the internals of the engine and it would rust all the metal in the engines. Other than that any 2 stroke pre mix outboard can be run on a 100:1 ratio because it's been proven through tests and engine break downs that I have read. I myself do not run 100:1 but I know running 65-75:1 will not hurt anything internally especially using full synthetic oil. That imo is a myth. If you research there is tons of people running our mercs on 80:1 amsoil with incredible results and they have ran that particular ratio for over 15yrs and I would say 15yrs with no issues is proven to work. Now I'm not saying to do that I'm just saying 50:1 it allot of oil if you really think about it. I will experiment with 70:1 just to see if idling is better,that's all I'm trying to accomplish, plus using only a few ounces less oil per 6 gallons will last much longer. There is no way imo that cutting back only like 3 to 4 ounces of oil will destroy our motor,if it runs cleaner,idles better and smokes much less than I will take it. There has never been any proven evidence that a lighter oil ratio other than 50:1 is bad for our mercs or any 2 stroke pre mix. But it has been proven a 75-80:1 oil ratio has great results as in less smoke,idles better,less fouled plugs,overall just a better running outboard. If a Yamaha 2 stroke can do it our merc can. If your comfortable at 50:1 by all means stick to that,I want to just experiment with it,if it doesn't improve smoke,idling,or overall better performance than I go back to the 50:1 oil ratio. No harm no foul.

 

[flyingscott]

Why do you say not to run it on anything but 50:1,actually my merc manual says 25:1 on break in then 100:1 for normal regular use which I know it can be run on that ratio because yamahas do and the engines materials are the same. I just know from reading the reasoning for the companies going back to the 50:1 oil ratio was not for any wear or tear from everyday use it was from sitting for months and months that there wasn't a good enough oil film left on the internals of the engine and it would rust all the metal in the engines. Other than that any 2 stroke pre mix outboard can be run on a 100:1 ratio because it's been proven through tests and engine break downs that I have read. I myself do not run 100:1 but I know running 65-75:1 will not hurt anything internally especially using full synthetic oil. That imo is a myth. If you research there is tons of people running our mercs on 80:1 amsoil with incredible results and they have ran that particular ratio for over 15yrs and I would say 15yrs with no issues is proven to work. Now I'm not saying to do that I'm just saying 50:1 it allot of oil if you really think about it. I will experiment with 70:1 just to see if idling is better,that's all I'm trying to accomplish, plus using only a few ounces less oil per 6 gallons will last much longer. There is no way imo that cutting back only like 3 to 4 ounces of oil will destroy our motor,if it runs cleaner,idles better and smokes much less than I will take it. There has never been any proven evidence that a lighter oil ratio other than 50:1 is bad for our mercs or any 2 stroke pre mix. But it has been proven a 75-80:1 oil ratio has great results as in less smoke,idles better,less fouled plugs,overall just a better running outboard. If a Yamaha 2 stroke can do it our merc can. If your comfortable at 50:1 by all means stick to that,I want to just experiment with it,if it doesn't improve smoke,idling,or overall better performance than I go back to the 50:1 oil ratio. No harm no foul.

Run what you want it's your motor but I have rebuilt several of these and they are not cheap to do oil is cheap insurance. My manual says 50-1 so I will stay 50-1 your mercury is not a yamaha that's not even a comparison to be made the Yamaha is a better motor. I have run 100-1 since the 60s I know all about it I won't run my 25 hp on it ever.

Let me give you a price list for rebuilding one of these.
re-chrome $225 a hole
re-sleeving $300 a hole
Pistons $134 each have to use mercury pistons unless you re-sleeve then you have to use wiseco
Main bearing $105 which I have seen fail enough
Those are just the major parts so no I won't cheap out on oil and Have never had a problem idles great and trolls all day.

Let me say again your motor is not a yamaha I have never had a wrecked yamaha. I could start a parts warehouse off of the burned up Mercury 25 hp motors I find. Glad you like your motor but I am not sure I would go crazy with less oil.When that motor burns up it's disposable. It's not our motor I won't run my motor on 100-1 so I will never find out.

 

[boater1234]

How can u say a Yamaha is a better motor,that is furthest from the truth. That may be your opinion and I respect that but that is just opinion. There is nothing special about the Yamaha that is any different then the merc. It's funny how everyone says the manufacturer knows the engine best,correct, so if that's the case why does nearly everyone run 50:1 in the Yamaha when everyone clearly knows and states on the motor 100:1,but yet no one will do it. I find that humorous. Most,not all,but most won't run the 100:1. I hear it so much ,follow the manufacturer specs but you know as well as I do more than half don't. I agree with most everything you said except yamaha is better, also I don't think mercs are better but I do know our mercs or at least mine will beat a 25hp Yamaha because I've done it several times with my buddy who has the same boat and I actually had more weight in the boat and beat him from one side of my lake to the other. Are yamaha motors awesome, absolutely, but if I got 2 brand new engines,25hp I would go merc all day long because I love the power.

 

[boater1234]

I actually have 2 manusls,funny,one says 50:1 and one says 100:1 for normal running unless it's commercially used,then go the 50:1. Obviously at one time the 100:1 was excepted till all that crap happened with johnson/evinrude were people were leaving outboards for months at a time and the little oil that was being used wasn't I guess enough to coat the engine when sitting which caused rust in the engine and blown powerheads,but nowhere does it say running 100:1 will hurt a thing,in fact allot of stuff I have read is completely opposite, allot of people believe it keeps an extremely clean engine that way,no carbon buildup and low smoke. Like I said me personally I will stay in the middle because I know it's the best of both worlds, not to much and not to little oil. A 2 stroke is absolutely supposed to smoke but not like a chimney and at the 50:1 ratio I believe it's a bit overkill,again just imo. There is no way imo running just a hair leaner will hurt anything, I'm not talking about taking half the oil away,just a couple to a few ounces at best to see only if it runs smoother,idles better and less smoke, if it doesn't then one tank won't hurt it and I go back to the 50:1. I guess I will be the test guinea pig, lol. I will let you know if it makes a difference running wise when I start the hair bit leaner mixture. Thanks for all the info.

 

[boater1234]

Most motors that get burned up is also lack of maintenance, not oil ,that's a fact. Most people don't maintenance there motors like they should,as you said those mercs could have blown due to overheating which is not oil related but water pump related usually and the manifold gasket failure. Good thing is I have very little invested in both my mercs so if they blew they would,be parts motors anyways so that is not really a concern to me,not that I wouldn't be upset but not to concerned. Also when most motors blow very,I mean,very few blow from oil related issues that I've seen anyways. 95% of the time it's owner neglect,those motors would still be running if taken care of. I have bought and sold many mercs and yamahas and never had issues with either of them. I think the yamaha is a great motor but no better than my merc. My 93 is 24yr old regardless of hrs and it runs like a top except for the excess smoke which just maybe the way it runs because the 02 does the same. Most things I have read stated these mercs are nearly bulletproof if TAKEN CARE OF.Again,owner neglect is usually the cause of a blown motor. Sorry so long,lol.

 

[boater1234]

Heck,maybe I should just sell both mercs and get a 25hp suzuki efi,they are awesome outboards. Yes,4 stroke but awesome power and reliability.