Will STP cure lower unit leak?

[jwilkey84]

I was told by a man at the local marina that if I mix 1/2 STP oil treatment and 1/2 lower unit oil and put it in, that it will usually cure any small leaks that the lower unit may have. Has anyone heard of this? Does anyone else have any "cures" that I might try before tearing into all of the seals?

 

[tashasdaddy]

Re: Will STP cure lower unit leak?

replace the washer seals on the drain and vent plugs. #1 place for water intrusion. should be changed every time the plug is removed.

 

[WillyBWright]

Re: Will STP cure lower unit leak?

I wasn't aware that an engine oil treatment was also appropriate as a gearlube treatment.

Seals wear out from hours, rot from age, or are damaged by fishline or other causes. I suppose it might be worth a try, but I'm skiddish on 50/50. But only if you trailer the boat. I wouldn't trust it in a moored boat, or in any situation where gearlube condition isn't easily monitored.

 

[Scaaty]

Re: Will STP cure lower unit leak?

Ya talking that thick heavy stuff ya can barely get out of the bottle? See no reason why it wouldn't slow a tiny leaky seal, but have fun trying to get it in!
If the motor's worth it, seals are easy to replace

 

[Outsider]

Re: Will STP cure lower unit leak?

You can pay to have the unit rebuilt, or you can pay to have the unit replaced after the snake oil remedy fails to perform ...

 

[WaterWitch2]

Re: Will STP cure lower unit leak?

I have never had any luck with any kind of stop leak additives.

 

[jwilkey84]

Re: Will STP cure lower unit leak?

Thanks for the 2 cents guys. I'll try it, because it isn't my boat. It is for a buddy with not much money. How many seals are there to replace should I go ahead and do that. I am sure I can do it myself, right? It cant be that hard can it? There would be a vent and drain screw seal and I am guessing there is at least one behind the prop. Where else would I expect seals? Can I buy a kit or would I have to get them individually? It is for a 1958 merc 58a, but it runs good so I want to maintain it. Thanks

 

[studlymandingo]

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Personally, I would remove and replace the shaft seals first thing. Use marine gear lube and go from there.​

 

[Scaaty]

Re: Will STP cure lower unit leak?

Thanks for the 2 cents guys. I'll try it, because it isn't my boat. It is for a buddy with not much money. How many seals are there to replace should I go ahead and do that. I am sure I can do it myself, right? It cant be that hard can it? There would be a vent and drain screw seal and I am guessing there is at least one behind the prop. Where else would I expect seals? Can I buy a kit or would I have to get them individually? It is for a 1958 merc 58a, but it runs good so I want to maintain it. Thanks

Damn right its worth it...find an old Merc freak near ya...don't do it yourself..thats a Gem there...'course I like old Mercs..

 

[diaric]

Re: Will STP cure lower unit leak?

first, figure out which seal leaks, fill and vent screw gaskets are most common, then the lower water pump seals. the prop seals usually are least likely. you can find your parts here
http://www.oldmercs.com/mark58a.html

 

[fishingdan]

Re: Will STP cure lower unit leak?

You were told that magic stuff will fix small leaks. Do you have small leaks? How do you know?

If it is truly a slow leak, I find it easier to just change the gear oil more frequently. As I'm doing this, I'll be able to tell if the condition worsens and then replace the seals.

As mentioned above, losing the vent and fill screws seals is the most common cause for water in the lower unit. For some reason, those things can just disappear.