Re: 84 mercury blackmax v-150 lower unit porblems
The lower unit drain is on the under side of the big, round, housing that contains the prop shaft and the prop. There is a SS screw there with a blue sealing washer. Up on the side of the lower unit, above the small water inlet holes (forget which side it's on) but before you get to the anti-vent plate is a similar screw which is the vent for filling the lower unit. It too should have the blue washer.....these two seals must be in like new condition for you to keep water out of the lower unit gears.....I only use these and I get them from a Merc dealer.
Put a suitable pan under the lower unit, pull both screws and let the lower unit oil drain.
Refill with Quicksilver heavy duty/high performance/ or whatever is on the label....forget and the bottles are in the shop. Refill procedure is to insert the oil adapter that comes with the bottle of oil into the lower hole and force oil into the lower unit until it appears at the upper vent hole..keep filling till the bubbles pretty much clear up and install and tighten the top screw. Remove the fill spiggot and quickly install the lower screw tightening both as snug as you can with a screwdriver and your bare hand.
The oil that comes out usually will contain some metal particles. Some engines have magnets embedded in the lower screw (a little black magnetic cylinder) and if your engine has one, you should clean off the metal particles while the screw is out. It's obvious that you are going to have shavings there, otherwise Merc wouldn't have a magnet down there to collect them.
Merc fluid is blue-black. Any yellowing is water and bad news...the more yellowing, the more potential problems you could have. I have used Pennzoil lower unit oil bought from WW and it's honey colored.....but it is clear. Water yellow is like chocolate milk consistency just gets yellower as the water content increases.
After you finish changing your fluid, pull your prop nut and nut retainer off and mark your prop at the rear. Mark a straight line from the spline part of the prop hub all the way out till you get to the exhaust openings. Put the nut back on, torque to 55 ft/lbs (good and tight....not bolt breaking tight) line up a slot in the prop and bend your nut locking tangs down.
Take the boat out and run it just until you experience your problem. Get back to the dock or where ever and remove the nut and keeper. Look at the line you made. If it is not a straight line like you marked, your problem is a spun hub in your prop and either a prop shop needs to replace it or you need a new prop.
HTH,
Mark
