Mariner 25hp 2-stroke Long shaft; s/n identification?

I have a Mariner 25hp, 2-stroke, long shaft engine on a recently purchased pontoon. Serial Number is OB222153, what year?

Welcome to the board. You have a "manufactured in" 1987, Mercury built model. It is identical to a 25 Merc, just different paint and decals.

Merc "serials" are actually "production numbers" and do not have the date encoded in them at all. Merc does this so a dealer never has "last year's model" on the floor. So while it was built in 87 it could have been sold as a "brand new, current model" all the way up to mid 1994 when they made some "minor" changes to the model. It stayed in production until about 2005 and was an outstanding model with a great reputation (so parts are plentiful and available).

Thank you! So to purchase a manual, I just need to find a manual for a 25 hp Merc? AND, it appears that I need to remove the lower unit to service the water pump impeller...? I appreciate your assistance (makes my grandkids happy also!)...

Yes to all your questions

You have a couple choices for a manual. For about 35 bucks you can go with a Seloc's manual for "Mercury's"(sold in book form or electronic - don't get a Mariner manual, those deal with the Yamaha build models - totally different beast). It covers all 1&2 cylinder models so some diagrams etc are of slightly different models/horsepowers but it is written for the "back-yard mechanic types" giving you step by step instructions and a list of do's/don'ts. Clymers also produces an aftermarket manual but in general I find them "lacking" in comparison.

Your other choice at $80+ is a factory service manual. Merc part number 90-826883R2 in this case. It is very specific to the 20 and 25 horse models (which share about 99% of their parts) but it is written for "Merc tech's", so it makes assumptions that you already understand the do's/don'ts etc - but if you ever do major work (as opposed to regular maintenance), it's a definate must.

The small Merc's, 25 horse and under, produced between 1986 and 2005 are truely outstanding little motors. The powerhead and gears were built by Yamaha, the ignition is Merc's Thunderbolt 4 and the carbs are Walbro's - possibly the best combination of parts ever assembled.

Very little goes wrong and there are no (NO) chronic or legacy issues with these models. I would check to make sure it has a thermostat. Merc tried saving a few cents by not installing a thermostat in all models (they sell for about 20 bucks). While you can run it without one it has a noticably better idle with one installed (and it will lengthen the lifespan of the motor).

Other than that, I would change the gear oil every year (takes less than 9oz of gear oil - any 80, 90 or 80/90 weight oil that is GL-5 rated is perfect - as long as it has GL-5 on it, you don't need to pay double for "marine" gear oil). I personally change the plugs each year in my two small Merc's. Only use NGK plugs (BP8H-N-10's gapped at .040" in this case). They sell for about 3 bucks a piece, so a cheap "tune up". If you can't find NGK's you can run Autolites but NOT Champions. Champions resistance isn't designed to work with the high voltage coils used in this ignition and while they will fire, the performance will suffer and the plug life will be cut very short.

Since you have just picked this motor up, definately change the impeller (and yes, you have to drop the lower unit - Seloc's will walk you through it). Merc recommends replacing the impeller every 3 years or 300 hours of use, whichever comes "first". I run my motors alot and live in Canada (temp swings between the 90's and -20's) so I replace them every second year - figured the rubber has taken enough abuse by then (and 18 bucks for an impeller is alot cheaper than an overheat).

That's about it for maint - gear oil, plugs, impeller and check the thermostat (or install one). With minimal care you could easily get another 20 years of troublefree service from this motor.

Thanks once again! I was too quick on the manual order and ordered the Seloc manual for a Mariner. After reading your info, I also ordered the similar manual for the Mercury product and will return the Mariner manual once it arrives. Interesting comment about the thermostat. I'll check that and make certain there is a t'stat installed before we get the motor wet. I already changed the gear oil, and agree with you that the word 'Marine' on the jug just drives up the price... I appreciate you sharing your knowledge on this project I have!