in-line 6 165HP - end of it's days?

Dear All,

The problem: A small amount of water is making its way into the oil of my in-line 6 165 HP mercrusier from 1975. The quantity of water is very small (after sitting for a week, the water in the oil settles to just barely touching the dip stick end). The water doesn't seem to boil completely off even after running the engine for an hour or so but it does get whipped into a small amount of froth that can be seen on the top of the dipstick (though the oil remains clear and clean.)

Here is my blindlly ignorant diagnosis: It seems like there is a slow leak in the block somewhere. It's not the head gasket since the engine starts up without any problem and runs fine (indicating good compression) so it has (or does it?) to be a crack in the block.

Prognosis: not worth repairing?

Sincere hope: I am missing something obvious that would suggest something other than a cracked block to explain water in the oil.

Any ideas would be very welcome!

Re: in-line 6 165HP - end of it's days?

give this a click are a read. the service bulletins in the link too.
fwiw. i had some water in my oil too right after i got my boat. manifold and riser i'd think were original from '75. i read the service bulletin and changed my oil right away the removed the manifold and riser as mine were rusty on the outside so seemed suspicious from just that. i confirmed the manifold by filling up the water jacket of the manifold while off the engine and sitting on the ground. next day the water jacket was empty and the exhaust runner full. i replaced the manifold and + riser since i figured it wasn't far behind the manifold and then i was hip. i think acetone may find leaks better than water. someone will correct me if i'm wrong on the acetone.
anyways. that link should get ya going in the right direction.

Re: in-line 6 165HP - end of it's days?

I have 3 of these engines. One engine is basically a scrap iron as a result of it being ran with a rotted out manifold. Yes rotted out, not cracked!!!!!!!!!!!

I test the manifold at the beginning and end of each season. If you catch it in time, the engine will be just fine.

Re: in-line 6 165HP - end of it's days?

Thanks Ziggy and Fordiesel.

The boat is a freshwater cottage boat and is put away for the season. If I lived closer I would take the mainfold off over the winter and test it. As it is, a fairly competent mechanic changed the oil and winterized it before putting it to bed for the winter. I need to make a decision before spring on what to do with it. These engines are reliable and easy enough to understand but in the super heavy starcraft 17 ft fiberglass "american" that mine is in, it drinks fuel and has to go at least 2700 rpm to stay planing so there is no taking it easy to save fuel. Cost/benefit analysis will be needed. Even if it is "just" the manifold, replacement ain't all that cheap.

Sorry, the above is just me thinking aloud!

Re: in-line 6 165HP - end of it's days?

ziggy said:

give this a click are a read. the service bulletins in the link too.
fwiw. i had some water in my oil too right after i got my boat. manifold and riser i'd think were original from '75. i read the service bulletin and changed my oil right away the removed the manifold and riser as mine were rusty on the outside so seemed suspicious from just that. i confirmed the manifold by filling up the water jacket of the manifold while off the engine and sitting on the ground. next day the water jacket was empty and the exhaust runner full. i replaced the manifold and + riser since i figured it wasn't far behind the manifold and then i was hip. i think acetone may find leaks better than water. someone will correct me if i'm wrong on the acetone.
anyways. that link should get ya going in the right direction.

Click to expand...

Acetone works but expensive and very flammable. Rubbing alcohol much safer

Re: in-line 6 165HP - end of it's days?

David Foe said:

Cost/benefit analysis will be needed. Even if it is "just" the manifold, replacement ain't all that cheap.

Click to expand...

A brand new manifold will cost $400.
A brand new riser will cost $120.

Then you have brand new parts. If you are considering another boat, unless you are looking at new, then you have questionable life left in the manifolds of the new boat.

So.... the benefit related to cost will probably be to stay with your existing boat - assuming everything else is good with it.

But it sounds like you may be simply wanting to buy a new boat!

Re: in-line 6 165HP - end of it's days?

David Foe said:

Thanks Ziggy and Fordiesel.

The boat is a freshwater cottage boat and is put away for the season. If I lived closer I would take the mainfold off over the winter and test it. As it is, a fairly competent mechanic changed the oil and winterized it before putting it to bed for the winter. I need to make a decision before spring on what to do with it. These engines are reliable and easy enough to understand but in the super heavy starcraft 17 ft fiberglass "american" that mine is in, it drinks fuel and has to go at least 2700 rpm to stay planing so there is no taking it easy to save fuel. Cost/benefit analysis will be needed. Even if it is "just" the manifold, replacement ain't all that cheap.

Sorry, the above is just me thinking aloud!

Click to expand...

If you don't mind the hassel, you can drain the log each time you shut it off by fabing up some hardware store bits to make a quick drain.

The hazard comes when the engine is off and the manifold is draining into the open ex valves.