Mercury 200 HP 2 Stroke Losing Compression after Engine stops (Help)

[texasrush]

I have a Mercury 200 HP 1996 and I had a Over heating alarm so I backed off and crawled into the Dock. We replaced water pump and check out rest of cooling system all seems fine. When we did a compression test all cyclinders are at 120ish but when you stop the engine the pressure leaks out. I thought it was the tester but it did the same thing with another tester. Engine runs fine but it over heats. Head Gasket??? or ?????

 

[JB]

Re: Mercury 200 HP 2 Stroke Losing Compression after Engine stops (Help)

Howdy, texasrush.

Welcome to iboats.

What compression test are you using? It is normal for the compression to drop when you stop cranking, but most guages hold the peak until you release it. Sounds like you have a bad guage or you are not using it correctly.

Your problem is not compression or head gasket. I think you overlooked something in the cooling system or your timing is too far advanced.

Do a link 'n' synch by the book and let us know what happens.

Good luck.

 

[texasrush]

Re: Mercury 200 HP 2 Stroke Losing Compression after Engine stops (Help)

I have used the tester before and I'm not releasing the pressure it just drops out. I thought the same thing that the testers was broken but it did the same thing with another tester. very starnge .....

The boat only overheats when you run it over 3000 RPMS

 

[CharlieB]

Re: Mercury 200 HP 2 Stroke Losing Compression after Engine stops (Help)

The boat only overheats when you run it over 3000 RPMS

And this is AFTER you serviced the water pump?

You may have leaking headgaskets from the overheat. Cyl pressure increases with throttle opening/load, a small leak may not displace enough cooling water until 3K.

While they are off, check them carefully for flatness/warp.