1970 Merc 500 lower unit takes on water. Need advice on where to start.

[Roadblock]

Mind you that it's not MUCH water at all but I've noticed that when I come back in from the lake my lower unit gear case has milky white-ish colored gear fluid in it.

I always drain it right away and let it drip for a couple hours then fill it right back up til it over flows to push any water droplets out of the casing and she is good to go. The gear oil never leaks either. Also if I run the engine on water muffs in the driveway, no water seems to get into the gear case so I'm guessing it only happens when I've got the boat under load on the lake and I'm out ripping around. Again when I drain the gear oil there is no standing water that pours out. The gear oil is still nice and thick, it's just a little milky white from water contamination.

I just bought this motor from a family friend who says he is 100% sure he changed the impeller last season.

I know you can have these pressure tested but I'm wondering if there might be something simple I should check. Also I plan to change the impeller and seals related to it here soon.

I have a question about water flow too. How much should I be seeing? It flows steady but I don't really notice that much of a difference between idle and WOT. I mean at idle sometimes I see a um trying to think how to explain this. OK for you guys! You know how when you take a leak and your about done and you slow down and give it that final push? The stream starts to die off and then comes back but it never really stops all the way? LOL! Yeah best way I could think to explain it. Anyway that is what my water pee hole thingy does at idle but when I'm WOT its just steady like its taking a leak. I never see water shooting out fast like a super soaker stream. Is this correct for an older engine?

Anyway I'm just wondering where to start with the water contamination. Do I just get it pressure tested or is there a common quick to check seal or something that would get replaced with the impeller that causes this?

Thanks guys and gals!

 

[Georgesalmon]

I think that the bottom of the water pump is also the top of top of the gearcase and contains the upper seal that keeps the water out of the oil. Its possible that could be messed up if only the impellor was changed and not the whole pump housing. Anyway that's the way it is on my 115 of the same vintage. Might get the whole water pump and change it. iboats has them and they aren't real pricy.

 

[Roadblock]

OK well it sat for a couple days and I still have that milky white fluid. I did not see any noticeable amount of water come out when draining but the fluid seems to be contaminated non the less.

Maybe I should just start with a full water pump kit?

 

[racerone]

You start this project with a pressure test.---That is how you find what is leaking .-Then make the correct repairs.

 

[hotrod53]

If you're lucky, its a seal up near the water pump. If you're not lucky, its a seal in the lower unit. Pressure testing will smoke it out. Did your relative put the fiber seals back on the drain and fill plugs or are they shot?

I have a '77 Merc 50... these motors do not pee hard even with a new impeller. As confirmed with the original owner of mine.... upon startup it takes about 15-20 seconds before you see any pee at all, there's no thermostat but its filling the block. At idle you will at first see bubbles and dribbling. If you rev it once from idle you get a steady but weak pee. Anything above idle you get a good stream. At high RPM you get a good pee like you do after having a few beers.

 

[Roadblock]

10:06pm, Monday July 14th. I'm going to go drain the case right now and I will update. It's been sitting for 2 days since my last run.