7.4 Merc Oil Issue

[BottomLineMD]

I have 7.4 merc on my 1980 270 that was replaced in 2003 and currently has about 400 hours on it.

There was a reasonable amount of oil in the bilge. I cleaned it out some to see if I could determine the source, and it feels/seems like that oil may be coming from the back of the engine near where the outdrive attaches. The top of the engine is clean, and gives no indication that there is an oil leak from that area. It also doesn't seem as though the pan or gasket around the pan are leaking. Any ideas what the source of this oil could be?

 

[moparlvr4406]

rear main seal
pan gasket
oil sending unit
oil filter adapter
thats about all thats back there

 

[Bt Doctur]

carrier seal in drive leaking oil into the bellow then into the bilge

 

[BottomLineMD]

What is the best way to determine which of these it could be without removing the whole engine.

Also, if it helps, the oil pressure and temp holds with no substantial changes (goes down a bit after the engine gets warmed up, but nothing abnormal). What level of concern should I have for this issue? With close monitoring of oil levels and proper cleaning (so as to not discharge into the bay) can we get through the season (5-10 hours)?

 

[moparlvr4406]

if you can get a visual ... you can put a flourescent dye in the oil and look with a black light to determine the source of the leak

 

[BottomLineMD]

Thank you for your help. I will try that.

 

[moparlvr4406]

it and the led black lite can be purchased at about any auto parts retailer...make sure you specify OIL dye though

 

[Saverio]

I been using my iphone and put it on video and let it record and hold it alll around and under stuff. my old boat the engine compartment was so tight thats how i found my trans cooler leak.

 

[northern]

How much oil is it using in 50 hours

 

[Bob & Sue]

if you can get a visual ... you can put a flourescent dye in the oil and look with a black light to determine the source of the leak

Good tip never thought of that one.

 

[Chief Alen]

Smell the oil you will know if it's drive oil or not.

Drive oil then the drive needs sealing.

Engine oil you just have to check the dipstick to see if the level is lower.

 

[BottomLineMD]

Well, it is much more than a little leak. It basically puked the oil out on the last trip. Almost 4 quarts in a little less than an hour of use. This seems to no longer be the self-diagnosis type of problem and is now an expensive type of problem.

If anyone has a good Merc expert near Baltimore, I'd appreciate some tips. This is my very humble introduction to boat ownership!

 

[Bt Doctur]

some places to check are the oil pressure sender for the gauge, the oil pressure switch for the electric fuel pump(if equipped), dist base gasket, oil pan drain plug/remote hose, remote oil filter.

 

[1990-270-da-lover]

I found that the oil filter cap that goes over the normal mounting for the filter down on the port side of the engine was loose, took it off, cleaned seat and gasket which was in great shape, and reinstalled. Solved what was a pretty good sized oil leak that I was experiencing. I did this when I had the manifolds/risers off for replacement, and it was much easier to access, but you could get to it even with the manifold in place.

 

[BottomLineMD]

Thanks everyone for the input. Turns out it was the remote filter unit. Two small leaks in the hose, and the copper nipple had totally disintegrated. Replaced and good as new.

 

[1990-270-da-lover]

Great! Glad it was a relatively inexpensive repair. I'm going to check mine now hat you said the nipple was totally disintegrated.