I'm leaving an oil slick

wrestling coach

wrestling coach

Petty Officer 1st Class
Joined
Jun 27, 2011
Messages
210
Pulled into my slip today and while I was tying up I noticed the rainbows coming from the rear of my boat. Came back an hour later and the oil slick was gently extending from the rear of the boat. Hit the trim button up and down and the oil slick increased significantly. I pulled the boat out and it is on the trailer. 1983 Merc 470 and I'm not sure of the outdrive. Pre-Alpha? What am I looking for here?

Dennis
 
M

MarkSee

Lieutenant Junior Grade
Joined
Sep 10, 2010
Messages
1,172
Re: I'm leaving an oil slick

The braided trim hoses that you see going to the trim rams can develop a hole and leak; they did on my Maxum and I replaced all 4.

Look inside the boat for the trim pump, open the cap and see if the fluid in there is milky in color.
If so, water has gotten in there mixed with the oil and will need to be flushed.

While on the trailer, have someone operate the trim switch while you look at the hoses to identify if one of those is leaking or not.

Mark
 
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makonnen

Petty Officer 2nd Class
Joined
Apr 4, 2012
Messages
184
Re: I'm leaving an oil slick

In addition to MarkSee, check the other easy stuff. Trim tab hydraulics, check the leg drain plug and filler plug ... are they tight? Is the little round gasket split b/c of overtightening? Are they double gasketed?
 
wrestling coach

wrestling coach

Petty Officer 1st Class
Joined
Jun 27, 2011
Messages
210
Re: I'm leaving an oil slick

OK. Thanks guys. I'll check for oil on those stainless braided lines as well fill and drain plugs for lower unit. Don't have trim tabs. I'll let you know what happens. In addition overnite while sitting on the trailer in the trailering up position the drive has fallen back to its lowest position.

Dennis
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: I'm leaving an oil slick

Are you sure it's oil, and not raw un-burned fuel from your engine idling way to rich?

Usually what ever is leaking will also have a low reservoir or low oil. Have you checked the drive gear lube? Trim pump oil, trim tab oil if you have it. If milky gear lube, you may have a hole in your ujoint bellows.
Pull it out of the water, and operate everything that is hydraulic and see what is leaking.
 
wrestling coach

wrestling coach

Petty Officer 1st Class
Joined
Jun 27, 2011
Messages
210
Re: I'm leaving an oil slick

Don,
I considered the exhaust and rich mixture. However two things: The plume of oil increased significantly when I used the trim button and the drive dropped from full up trailering position on the trailer last night.
 
W

wardfamid

Cadet
Joined
Aug 27, 2011
Messages
10
Re: I'm leaving an oil slick

Your hydraulic hoses are bad or cracked. There are two on each side of the outdrive. When you replace those, re-fill your reservoir with whatever oil it desires.(it will say on the side of the reservoir.) The reservoir is to the left of the starter. The fill plug will be on one of the corners of the reservoir. Here is the link for new hoses. Or go to a local marine shop they usually have them in stock. http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=79170&ivar=images/COMMON/39585.png&inbr=1595&bnbr=160&bdesc=TRIM+CYLINDERS+AND+HYDRAULIC+HOSES%28EXTERNAL+LINE%29
 
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makonnen

Petty Officer 2nd Class
Joined
Apr 4, 2012
Messages
184
Re: I'm leaving an oil slick

Coach,

You're getting some good advice here. But I tihnk you answered your own question. Either the oil is leaking back to the reservoir or outside of the hydraulic cylinder.
 
wrestling coach

wrestling coach

Petty Officer 1st Class
Joined
Jun 27, 2011
Messages
210
Re: I'm leaving an oil slick

As a follow up on my oil slick. Found one of the upper power trim hydraulic lines split inside the stainless braided line. I replaced both of the upper hoses, bled the system and topped off the reservoir and have been good. Thanks for all your help.

Dennis
 
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