Mercruiser 3.0 overheated, Is my motor shot?

[cyclops222]

Blown head gasket can be to....water ...exhaust ....intake or a oil channell.

 

[Scott Danforth]

Time to do a leak down test

 

[Kola16]

Alright. Sorry it’s been a minute to retest. Bought a new compression tester and here are the results…

#1 - 150 psi
#2 - 90 psi
#3 - 145 psi
#4 - 150 psi

Did a wet test on #2 and minimal change. Slightly over 90.

Could it be the valves for #2?

If I had a blown head gasket I would have two adjacent low numbers correct?

If it was the piston rings then the wet test would have increased the numbers?

Oh no that is a bummer.
Yes, it could be the valves for #2 cylinder, but you would have to do a leak down test.
A blown head gasket doesn't always happen between cylinders. It could also blow to a water passage.
A wet test should increase psi if the rings are bad or the cylinder is slightly out of round, yes, but not if the rings or cylinder is really bad.

Like Scott said, you need to do a leak down test to find where the air is escaping. Make sure both intake and exhaust valves for cylinder 2 are closed. Find where the air is hissing out and report back.

 

[Hatch19]

Hey guys sorry it’s been a minute since I’ve got back to this. I didn’t do a leak down test but decided to just run it in the drive way.

Starts up fine and doesn’t run any rougher than it did before (characteristics of an inline 4 maybe?).

Sounds perfect at idle and responds immediately when given throttle and doesn’t hesitate or “miss” but has a dull “tap or rattle”. Thoughts on what this could be? I’m guessing maybe just my burned up exhaust flapper? No water In oil after 15 mins of running.

I’ve got a video of the sound if helpful…

 

[airshot]

Often the flippers do rattle after an overheat. Do a quick compression test, if OK, then replace your flapper and be sure any bits and pieces are removed. Once your done, put boat in water and make adjustments to idle and idle speed, while in water and underway. My 3.0 idles nicely around 600/650 rpm

 

[nola mike]

Often the flippers do rattle after an overheat. Do a quick compression test, if OK, then replace your flapper and be sure any bits and pieces are removed. Once your done, put boat in water and make adjustments to idle and idle speed, while in water and underway. My 3.0 idles nicely around 600/650 rpm

already established that the compression test wasn't ok...

 

[Mc Tool]

already established that the compression test wasn't ok...

I would test it again after running it

 

[Fj40fiji]

The PO showed me receipts where he had head work done due to over heating my boat before I got it. I found flapper parts in the exhaust y pipe, and in the lower unit. Both flappers were toast.

 

[airshot]

The PO showed me receipts where he had head work done due to over heating my boat before I got it. I found flapper parts in the exhaust y pipe, and in the lower unit. Both flappers were toast.

If proper work was done, those flappers would have been replaced and the pieces removed!! Pull the head and get it reworked, valves ground, check all cylinders for scoring, reinstall with new head gasket and enjoy your boat. If you had done that to start....you would be cruising now, not still tinkering on your motor.

 

[Fj40fiji]

I’m not the original poster. My motor runs great. Other issues. . . Engine isn’t one of them!