Possible blown head gasket? Need Help!

[bulletfever159]

So today I pulled the plugs to do a compression check, some of the plugs had oil on them (No milky oil) I have oil and water mixing so I am trying to find the issue. All cylinders other than cylinder 4 had about 150 psi +/- 3. Cylinder 4 was reading about 60 psi. I also am waiting on a new thermostat gasket so I can do a coolant pressure test (I did the test but it appeared to only be leaking air from the thermostat, but I can't rule out a cracked block.) It is a 2001 Mercruiser 4.3L, Central florida, salt water. Thanks in advance!

 

[bulletfever159]

 

[Scott Danforth]

Pull the manifolds, most likely leaking water down the cylinders and rusted the valves

 

[tpenfield]

Sounds like you are on the right track with doing a coolant system pressure check. What help do you need?

Are the oily spark plugs just on one side of the engine? does it correlate to the 60 psi cylinder?

60 PSI is a fair amount of compression loss for a head gasket failure, unless it is a big blow-out.

 

[bulletfever159]

Sounds like you are on the right track with doing a coolant system pressure check. What help do you need?

Are the oily spark plugs just on one side of the engine? does it correlate to the 60 psi cylinder?

60 PSI is a fair amount of compression loss for a head gasket failure, unless it is a big blow-out.

Just trying to get any relevant experience from others to make sure I’m not doing anything extra. But for the spark plugs no, the ones that appear to have oil do not correlate with the low compression cylinder, and one is port side the other is starboard side. Hoping to be able to get the replacement parts for the thermostat housing so I can rerun the coolant compression check.

 

[Rick Stephens]

Oily plugs: I'm thinking valve guides, rings or intake gasket.

With good compression I'm down to gasket or guides. Valve guides will show up on vacuum gauge, unfortunately so will intake gasket.