Mercruiser 5.7 air in cooling system

[K_van]

I have a 95 Merc. 5.7L I/o raw water cooled getting air in the cooling system. The problem was first noticed by water temp fluctuates 100-150? in seconds back and forth. First thought it was an indication problem so changed sensor, not it. Changed thermostat 140? ,not it. Then noticed cooling hoses chugging. Now I figured it was a head gasket. Did a compression check all cylinders at 120 except 8 at 0. Pulled the valve cover and found #8 cyl intake rocker stud pulling out of the head so intake valve was not opening.. Removed the head and had it repaired. Just reinstalled the head, new gaskets and started the motor. Still have temp fluctuations and hoses chugging (seams like air). Any thoughts about what is causing this??

 

[alldodge]

Was the block checked for flatness?
Was the head also checked for flatness?

 

[Scott Danforth]

I hate pressed in rocker studs for that very reason.

regarding your air entering your cooling system, do a cooling side pressure test.

 

[K_van]

The head I had removed was checked and was fine. I didn't check the block. Also the oil is not milk at all and there was no sign of water on the pistons.

 

[alldodge]

Suggest putting some 1 1/4 ID clear hose between the intake hose and thermostat housing. If its sucking air you will be able to see it

 

[K_van]

I need to try that. Besides a head gasket or cracked head or block where can air be coming from?

 

[harleyman1975]

I assume that the impeller has been replaced?

 

[alldodge]

Bad seal on a hose

 

[K_van]

The impeller was replaced about 2 years ago. Seems to have good flow. I loosened one of the clamps on the thermostat housing while running and water started spraying out.

 

[alldodge]

Being your on the third season it might be the impeller if this is a bravo. Many get 3 years from an impeller, but some don't.

Might also have a restriction going to the pump, or after the pump in the motor or exhaust

 

[K_van]

Oh yeah sorry it's an alpha gen2 drive.

 

[alldodge]

Oh yeah sorry it's an alpha gen2 drive.

Then you should be good with the impeller