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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10620
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1998 250 Sundancer and the engine hydrolocked due

Customer Question

I have a 1998 250 Sundancer and the engine hydrolocked due to water getting into #8 cylinder after a rain storm. How is this possible?
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: Little additional information. When the boat started up there was a knocking noise, we shut the engine down and Sea Ray dealer confirmed #8 cylinder -0- compression with fresh water in cylinder, not lake water. Engine is 5.7L Mercruiser with B3 drive
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?
Customer: no
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Marine Mechanic about your situation and then connect you two.
Submitted: 6 months ago.
Category: Boat
Expert:  Tan replied 6 months ago.

Hello. My name is Tan.

What can happens is the exhaust valve sticks open from corrosion then when you crank engine up the down stroke of the piston pulls water in through the exhaust through stuck valve. Zero compression is a open valve.

Does this make sense?

Customer: replied 6 months ago.
how does fresh water get into the cylinder?
Expert:  Tan replied 6 months ago.

In through the exhaust. Where the water exits the engine the water that is already in the exhaust. With a stuck exhaust valve the down stroke of the piston sucks the water backwards through the exhaust riser. Back into that piston. The reason the other pistons don't have water is the valves are closed.

Customer: replied 6 months ago.
One theory was that during a heavy rain there was a large collection of water on the cockpit cover that was released when the rear snaps tore off. The water rushed to the back of the boat where the engine cover is and the rush of water wasn't contained by the shallow gully the engine cover sits in leaking into the top of the motor at the intake and TBI
Customer: replied 6 months ago.
the water in the engine is not lake water
Expert:  Tan replied 6 months ago.

I would think the water would have been in more than one cylinder with that scenario. How did it get in the flame arrestor?

And that doesn't explain zero compression in that cylinder? A stuck valve would explain the water and the zero compression.

Customer: replied 6 months ago.
the flame arrestor was removed when the engine was winterized
Expert:  Tan replied 6 months ago.

Why wasn't it put back on.

Well that still doesn't explain the water in one cylinder and the zero compression.

Customer: replied 6 months ago.
I didnt ask why they removed it during winterization. Obviously I'm not happy and think they're hiding something but cant figure out what took place. The engine only had 600 hours on it and was serviced by the Sea Ray dealer it's entire life. Now I'm being quoted $8,000 for a new long block because no one will rebuild the motor. Only complete engine assemblies..
Expert:  Tan replied 6 months ago.

Well I don't know what to tell you it's just things don't add up to that theory. Why zero compression and water in only one cylinder. If fuel goes in the intake it goes to all cylinders not just one. So if water enters the throttle body how is it water only got in one cylinder? Then how is it fresh water coming in through the throttle body caused the #8 cylinder to loose all compression?

If the engine isn't seized the worst case scenario in my experience is you need a valve job. A valve job won't cost more than $2,000.00.

Now I'm not there to do the diagnosising but I have been working on marine engines for over 40 years. So I'm not new to this industry.

$8,000.00 is rediculous. Here is a reman motor with warranty. $2,399.00. http://www.michiganmotorz.com/vortec-marine-engine-1996current-p-68.html

Expert:  Tan replied 6 months ago.

Please don't forget to positively rate my help as that is the only way I get credit for helping you.

Follow up questions are always welcome at no extra cost even after you have rated.

Thank you............Tan

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