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Author Topic:   Mercury 90 lower unit problems
baltica posted 10-16-2001 09:03 PM ET (US)   Profile for baltica   Send Email to baltica  
I am having trouble with my engine (a 1986 Merc 90), I think the lower unit is messed up. I just bought the boat this summer (a 16 foot 1970 Katama), and it ran fine the first time or two, but then the problems started. The engine runs well in neutral, even at high rpm, but has trouble getting up to higher speeds when its in forward gear. Sometimes, it will not go above 7-8 mph, other times it maxes out at around 25 mph, well below its capacity. You can hear the transmission struggling to get it on. So I pulled the plug on the lower unit, and out came stinking greyish oil- a real mess. Obviously water had seeped in. On top of this, the magnetic lower plug had some fine metal shavings on it (not lots, but enough to make me worried). I changed the lower unit oil, and ran the boat hoping this might help, but the problem is still there- boat runs fine at trolling speeds but can't get above 20-24 mph on plane.

So my questions are-
1) is the lower unit finished, or is there hope that I might be able to fix it?
2) Can I fix it myself, or is this a job for an expert? I've checked, and the cost of a replacement lower unit is over $1000....
3) given the age of the engine (1985), should I be thinking another whole engine? Since I just just bought this boat (my first Whaler), I'm relunctant to blow a wad on expensive repairs if this engine's days are numbered...
I need advice- any suggestions?
whalerron posted 10-23-2001 10:17 PM ET (US)     Profile for whalerron  Send Email to whalerron     
You should be able to have that lower unit rebuilt but the cost will depend on which parts need to be replaced. It cost me $350 to have the seals replaced in my 70hp Johnson so I would guess you are looking at that as a base price for the job. If the motor runs good, I would get an estimate on the lower unit. If you buy another used motor, you may have the exact same problems along with a motor that doesn't run right.

If you want to do the job yourself, you need a good manual and some special tools that you either buy or make.

- ron

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