Lower unit leaking oil...

JBFranklin · #1 07-08-2020, 03:36 PM

Some advice on oil leak problem?

I have 1985, 50HP Merc, that I have maintained well over the years. Due to the age of the unit, I am meticulous about winterizing and ensure each fall the motor is fogged and in the spring the gear lube is brand new. I use premium gas during the season as well. For a motor that is 35 years old... it runs very well.

About a week a ago I noticed that I had oil leaking from the top vent plug on lower unit. I saw that it was milky which means water had gotten in. I am on a bit of a budget, so here's my current diagnosis before I take it in:

It would appear that I have not replaced the sealing washers on the drain/vent plugs and this might be the cause. In fact there is no washer on the vent plug.

If its just the washer or even a new plug... this I can handle.

Has this happened to anyone before? Should I be looking at something more serious?

jungleboy · #2 07-08-2020, 04:23 PM

Change the oil and replace the washers and run it. If it is still getting water inside then it could be the prop shaft seal .

JBFranklin · #3 07-08-2020, 04:27 PM

Quote:

Originally Posted by jungleboy

Change the oil and replace the washers and run it. If it is still getting water inside then it could be the prop shaft seal .

This is what I am hoping. Thanks.

SamSteele · #4 07-08-2020, 04:30 PM

Since you are on a budget, my recommendation would be to:

1) Pull your prop and check for any fishing line around the shaft. If there is line there, chances are you have a blown shaft seal as the line puts pressure on it, causing to to deform and water gets in.

2) Drain your leg, replace the fluids and be sure to replace the seals/crush washers on your drain and vent plugs. Run the motor fully immersed in water for a while (lake is the easiest but could be a tank as well). After running it, check if your oil is milky again. If it’s not, your drain/vent plug seals were likely allowing water in. If it is, you either have a blown seal or a crack in your leg housing.

SS

58thecat · #5 07-08-2020, 04:34 PM

awesome feed back and by the way pulling off a lower leg is not a big job....youtube it....in fact youtube most of this and you would be surprised just how easy things are and save you lots of cash too.

do what was said in the posts first...keep it simple and good luck.

old dog · #6 07-08-2020, 04:36 PM

Just too add to this. Make sure u flush out the milky oil with some new oil to ensure it’s all out

old dog · #7 07-08-2020, 04:41 PM

If U take it in to be repaired And If u have never replaced the water Pump check out the price while the seal is being replaced

JBFranklin · #8 07-08-2020, 04:50 PM

Quote:

Originally Posted by SamSteele

Since you are on a budget, my recommendation would be to:

1) Pull your prop and check for any fishing line around the shaft. If there is line there, chances are you have a blown shaft seal as the line puts pressure on it, causing to to deform and water gets in.

2) Drain your leg, replace the fluids and be sure to replace the seals/crush washers on your drain and vent plugs. Run the motor fully immersed in water for a while (lake is the easiest but could be a tank as well). After running it, check if your oil is milky again. If it’s not, your drain/vent plug seals were likely allowing water in. If it is, you either have a blown seal or a crack in your leg housing.

SS

great advice. thank you vm.

JBFranklin · #9 07-08-2020, 04:52 PM

Quote:

Originally Posted by old dog

If U take it in to be repaired And If u have never replaced the water Pump check out the price while the seal is being replaced

You're saying it might worth doing this at the same time?

SamSteele · #10 07-08-2020, 04:55 PM

Quote:

Originally Posted by JBFranklin

You're saying it might worth doing this at the same time?

If you pull the leg off to replace seals, definitely do the water pump too. Cheap insurance.

58thecat · #11 07-08-2020, 04:58 PM

Quote:

Originally Posted by JBFranklin

You're saying it might worth doing this at the same time?

check the condition of the impellar...chances are if not done to date it will need to be....but like I mentioned do this yourself...I dropped my leg...replaced the impellar etc and back on under an hour....I pad and youtube….easy.

JBFranklin · #12 07-08-2020, 07:03 PM

Quote:

Originally Posted by 58thecat

check the condition of the impellar...chances are if not done to date it will need to be....but like I mentioned do this yourself...I dropped my leg...replaced the impellar etc and back on under an hour....I pad and youtube….easy.

Ok. Thx a ton. I had it done about 6 years ago. Will check it out for sure.

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jungleboy · #13 07-08-2020, 07:28 PM

Be cautious dropping the leg on a Mercury. I dropped the leg on a 4.5 merc one time and it was a nightmare getting it back together. I ended up having to remove the power head. Evinrude is easy for me but Mercury not so much. Probably an issue with that particular motor, it was a 63 vintage but I have been wary of them since.

58thecat · #14 07-09-2020, 01:42 AM

Quote:

Originally Posted by JBFranklin

Ok. Thx a ton. I had it done about 6 years ago. Will check it out for sure.

Sent from my iPhone using Tapatalk

6 years...replace it.....boat will start overheating....acting like it has a fuel/ignition problem by running and then shutting off but yet when running water will be coming out the engine as advertised.....so you chase another demon when all along it was the dam impeller.....spent a month doing this....hard lessons learnt on my end.....got lots of new used parts now but man I know that engine inside out

barbless · #15 07-09-2020, 05:51 PM

"I have 1985, 50HP Merc, that I have maintained well over the years. Due to the age of the unit, I am meticulous about winterizing and ensure each fall the motor is fogged and "in the spring the gear lube is brand new". I use premium gas during the season as well. For a motor that is 35 years old... it runs very well".

I notice you said you change the gear oil in the spring. Myself I do it in the fall when I put mine to bed for the winter. Reason being if it's milky then water has got in and that could potentially freeze causing other problems. Always change out your washers on drain and vent plugs with new. They are cheap. As far as I have ever seen there are washers on both plugs. Peace of mind.
As for the impeller, depends on how hard and how much you run your engine it could be done at least every three years. I do with my Yammy 150 2 stroke HPDI.

Moosetalker · #16 07-12-2020, 08:22 AM

I have an 75/76? Merc 7.5hp Thunderbolt used by a friend and due to myself being out hunting was unable to drain and change oil till November.

Long story short I was too late Line had wound about prop shaft buggered seal water got in and froze cracked housing took lower unit of and to Barry Jays.

They said replace every gear shaft etc pitted by time they were done Quote it was only $400 more to buy a B New 8hp on sale.

Only regret is new unit is about 30lb heavier than old one.