Merc 165 issues

[blowby]

Ok here goes.
My buddies boat has 165 merc.
He has owned it for 3 yrs, last year i went out with him 2x both times I noticed what I would consider an excessive amount of exhaust gas bubbles in the wake while trolling.
The boat has a rough idle at a certain rpm (1000 +/-)
It seemed to start fine and he ran it for quite a few hrs last year.
Last week I went out with him again, He had the same excessive exhaust "issue" and rough idle. The engine stalled once (it was up to operating temp) and was difficult to re-start.
Once re-started we trolled for 5hrs or so.

Upon returning to port we noticed a burning smell (oil).
I checked the engine and it was spouting the "milk of death" from the breather.

He later checked the plugs and the rear plug was coated with the oil/water mix.

He has the boat professionally winterized each year.
Do you think this is a head/ head gasket or exh.manifold/gasket issue.
Or worse.

thx.

 

[Don S]

Re: Merc 165 issues

What year, and is it a 4 cyl. or 6 cyl. Raw water cooled, or closed cooling system.

With oil/water mix coming out of the breather, it's no wonder it idled rough and died and hard to start.

I would say it's and engine problem, not an exhaust manifold problem. Water wouldn't get into the oil while it was running if it was the exhaust manifold leaking.

 

[blowby]

Re: Merc 165 issues

Not sure of the year (guess in the '70's) but it is an inline 6cyl.
Raw water system.
My guess is head gasket or cracked head.

Bryan

 

[blowby]

Re: Merc 165 issues

Ok, here is what was wrong.

Head gasket was leaking, as well as a crack in the manifold.

While I was at it, I took a look at the head and sure enough the valve seats were sinking.

Going to install hardened valve seats and head gasket.
I think I can fix the manifold leak as it seems to be only on the outside. (pressure test will confirm)

Remember if you have an engine built in the mid '70's or earlier you are likely running softer valve seats that required the lead in the fuel to cool and lubricate them.

Unleaded fuel will destroy them eventually.

Bryan