1984 90hp Merc blowing lower unit grease at high idle RPM from exhaust

[mgandalf]

I have a 1984 Merc 90hp motor that sometimes has a bit of trouble starting. When it does start, at high rpms, before I can throttle it back down it blows a bit of lower unit grease from the exhaust. I assume it's lower unit grease because of its gray color.<br /><br />Does anyone know the cause of this and if it's easily fixable? Should I be concerned?<br /><br />Thanks, Mark.

 

[hondon]

Re: 1984 90hp Merc blowing lower unit grease at high idle RPM from exhaust

That is more likely unburnt fuel.If you are unconviced of this just check the gearcase out.Remove the upper plug and stick a twist tie in there to check the level or better yet change the gearoil and have that unit pressure/vaccume tested.

 

[emckelvy]

Re: 1984 90hp Merc blowing lower unit grease at high idle RPM from exhaust

Pull the lower gearcase fill screw and check for oil color and water. <br /><br />You can definitely tell if it's gear oil leaking because it'll stink from the sulphur additives. Fuel/oil mix will have a lighter smell to it.<br /><br />What concerns me is, if it's grey in color, it could be emulsified water/fuel/oil mix. Coupled with the hard starting, leads me to think that maybe water is getting in the cylinders. <br /><br />After one of these episodes you should pull all spark plugs. Look for any that are unusually clean compared to the others; look for water droplets on the plugs.<br /><br />And a compression check might be in order to rule out ring/piston problems.<br /><br />If you find that you're getting water in the motor, you'll want to pull the exhaust covers for inspection, if it's in the bottom cyl only, could be a bad set of lower crank seals.<br /><br />HTH and Good Luck........ed

 

[JB]

Re: 1984 90hp Merc blowing lower unit grease at high idle RPM from exhaust

Not the fill plug. Pull the vent (top) plug. Filling is done from the bottom (drain) plug.

 

[mgandalf]

Re: 1984 90hp Merc blowing lower unit grease at high idle RPM from exhaust

Thanks for all your help. I've never done maintenance on a Merc lower unit. From what I can see there are two plugs, one on the bottom of the lower unit towards the back which would be the drain/fill. The vent plug is right above the prop on the fin, correct? Should the level be checked while the motor is tilted all the way up or all the way down?<br /><br />Thanks, Mark.

 

[Clams Canino]

Re: 1984 90hp Merc blowing lower unit grease at high idle RPM from exhaust

All the way down, fill from the bottom one till it runs out the top one. Drain from the bottom one to check color etc.<br /><br />-W