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lower unit 1983 150 hp

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hydroman316

New member
hey guys im new to this site and hoppin to get some good advice,i have a 83 150 xr4 merc,i had the lower unit oil changed b4 the season started,i checked the oil today and it was very milky and white,i was told im gettin water in my lower unit what would cause this,i had a whole new lower unit put on it at the beginning of the season,all brand new guts inside,and new drive shafts as well.as my old one seized on me while i was drivind late last yr,so with all new stuff im lost,any help would be great,

thx
hydroman316
 
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Re: lower unit

Water could be getting in from any number of points.

Common places are - the fill and vent plugs - they have a little rubber washer that goes under the head and is often overlooked or missing.

Three other common points of water intrusion are, the shift shaft seal, waterpump base seal and the big o-ring on the bearing carrier.

Since you say the lower unit is brand new, I would check to see if the gaskets are intact (or even there) under the fill/vent plugs.

Sometimes, no matter how well your lower unit is sealed you will still end up with milky gear oil.

In most of Canada and the northern States the wild temperature fluctuations cause different components of the lower unit to expand and contract differently which ultimately results in a little bit of water intrusion.

So if you live (up north) like me a bit of "milky" gear oil is almost a given. As long as you don't get water (which is separated from the gear oil and will come out first when you drain the lower) then you may be doing the best you can.

But definately check the seals at the plugs...
 
Re: lower unit

Good point, Graham. When I rebuild one of the later (to me) jet prop exhaust lower units, I orient ALL of the seal lips to keep the water out, and to heck with oil leaking out. Merc decided sometime in the '80s to put the big seal on the driveshaft lip down, to keep oil from leaking, while entrusting the far more important job of keeping water out to that tiny little seal above it! To heck with that.

Jeff

PS: The way I see it pressure equalization in a LU will occur after a bit of use. If the oil churning away down there builds up enough pressure to seep by a seal, the pressure will soon equalize and all will be well. I vacuum test ONLY to make sure water doesn't come back in as the LU cools back down (and the pressure inside is reduced). So far, so good.
 
Re: lower unit

thx for the input guys and ya i live in the great white north,cobourg ont ca,well i changed the oil again and took the boat out came home and took the drain plug out and water came out again,when i changed the oil it was like water,very thin and brown,weird wasnt even like oil,i am useing quicksilver lower gear oil,so i changed those washers and goin to take it back out tomo,(sun) and ill check the oil when i pull the boat out of the water and see where i stand,if those washers work and evereything eles is fine should i have any water in the LU,ands if so how much,
thx for the help guys.

hydroman316
 
Re: lower unit

If the washers were your issue you shouldn't get any water in the lower unit.

As I stated, particularly up our way where three weeks back we had frost then last week it was pushing the mid-90's you are never going to get a perfect seal in the lower unit - it's just expanding and contracting like crazy so some (moisture) IS going to creep in.

But, if it is "sealed" you should get nothing more than a little milky gear oil. If you actually have separated water then something is definately "leaking".

If that's the situation then pressure testing the gearcase is the easiest way to find the culprit...
 
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