Won’t idle 3.0 Mercruiser

[Aaron0801]

I have a 1988 invader with a 3.0 Mercruiser engine in it. Okay so first time I took the boat out, was out for about a hour when I realized the boat was over heating. Like maxed out at 240, I believe it blew the valve cover gasket because it started bellowing White smoke, not from the exhaust but from the oil dripping down onto the motor. I got it back it the dock and parked it. Then I changed the impeller, it only had 3 fins left. Started it back up and it will start after about 20 seconds cranking it with the throttle up. However it will not maintain an idle. As soon as I bring the throttle back towards neutral it bogs out. The temp is staying at 160, and it’s really not leaking very much oil, I still need to change the valve cover gasket. Help please, any advice is good advice.

 

[kenny nunez]

There is a good chance that the head gasket is blown out. Do a compression test. That will tell where the problem is.
You also need to find the rest of the missing impeller blades.

 

[dubs283]

Agree with Kenny on compression test and locating impeller pieces

Will add that 160 is too warm, most likely need a 143 degree thermostat. Verify actual temp with a laser thermometer

 

[Aaron0801]

Agree with Kenny on compression test and locating impeller pieces

Will add that 160 is too warm, most likely need a 143 degree thermostat. Verify actual temp with a laser thermometer

I found the missing pieces and removed them, I will do a compression test later today, thank you

 

[QBhoy]

I found the missing pieces and removed them, I will do a compression test later today, thank you

You may have an exhaust flapper that’s been melted and thrown parts down the exhaust too. If it had one previously.

 

[kenny nunez]

Worse than the exhaust you most probably melted the water pocket cover in the lower area of the upper drive shaft housing. If that happened then you will be losing water pressure to the thermostat housing, which will cause an over heating problem.

 

[Aaron0801]

There is a good chance that the head gasket is blown out. Do a compression test. That will tell where the problem is.
You also need to find the rest of the missing impeller blades.

Compression results are 40 in two cylinders, 15 in one and 90 in the other

 

[todhunter]

Compression results are 40 in two cylinders, 15 in one and 90 in the other

Not good. Time to pull the head.

 

[Bondo]

Compression results are 40 in two cylinders, 15 in one and 90 in the other

Ayuh,...... That's core motor, not a runner,.....

 

[Aaron0801]

Compression was 90, 40, 15, 40….. I changed all the spark plugs and it won’t start at all now

 

[Aaron0801]

Not good. Time to pull the head.

Do you think it’s still the head gasket, or something worse?

 

[dubs283]

Do you think it’s still the head gasket, or something worse?

Head gasket, tuliped valves, detempered rings, etc...

Guessing a valve job at a minimum, won't know for sure until you pull the head

 

[nola mike]

Head gasket, tuliped valves, detempered rings, etc...

Guessing a valve job at a minimum, won't know for sure until you pull the head

Warped head, block... Guessing that a HG alone wouldn't cause all 4 to lose compression unless it was really buggered

 

[Scott Danforth]

Do you think it’s still the head gasket, or something worse?

You burnt your motor up by taking it out without doing all the maintenance you do with new to you used boat.

You now get to pull the drive and pull the motor.

Get the motor on a stand and pull it appart

For reference. Cranking compression should be 145-150 in all 4 cylinders.