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Please help 165 merccruiser

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Boater1987

New member
Hi there. I finally bought my first boat. It’s a 18ft open bow 1977 glastron ssv177 165merc with a sei106 lower unit. Brand new lower unit came with it. I’m a car guy so I am knowledgeable with motors. I have good compression on all cylinders. No water or oil on spark plugs. Water is in the oil. It’s not sludgy or lumpy/chunky, or even thick. It is very thin. But it does have that yellowish mixed color. I’m not sure where to start. The previous owner gave me a new sei 106 lower unit for it and said just change the oil and put new lower unit on it. He seemed like an honest guy told me everything I think he knew that is wrong with it. It had a cut on the exhaust bellows tube as well. The motor starts right up. Idles great. Revs up fine no skipping or sputtering. Where could the mix be happening?
 
I’m assuming this is a straight 6 vs the I think later 4 cylinder 165hp ?

Crack in block or head, Head gasket, or exhaust manifold or riser gasket. exhaust and riser gasket issues would show water in the cylinders, which you don’t see.

Crack in exhaust bellows really doesn’t matter as it full of water Anyways as bottom is open to the prop hub.

also possible water Or condensation got in engine sitting in storage for a while.

My advice would be change the oil and see if it gets milky with running the engine. You may have to change it a couple times to get any moisture out of the engine and run it fairly hard and long to get it good and hot to burn off moisture or condensation in the engine. Get cheap Wally World oil and just put in 3 qts run it and check the oil.

if you still get moisture would look into Pressure testing coolant side and inspect the exhaust manifold and riser.
 
Ok. How can I tell if it’s a cracked block internal? Or cracked head without removing? Or is that the only way?
 
Last edited:
Boater1987 said:
Ok. How can I tell if it’s a cracked block internal? Or cracked head without removing? Or is that the only way?
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Pressure test the cooling system. Thus will be done slightly differently If you have FWC with a heat exchanger or raw water cooling , but basic idea is to isolate the cooling system by plugging the inlet and outlets with pipe plugs etc rigging up a connection to compressed air and a gauge. If it holds 15 psi Your ok.

I had bought a boat with a known cracked block and the oil was a milky paste vs what you describe as discoloration. It’s not uncommon for unused boats that site to get condensation in the oil that needs cooking off, which is why I suggested changing it until it’s clean and running it to cook any moisture off.
 
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