Catastrophic failure? Mercruiser 140

[boozer1966]

1984 mercruiser 140. Last year the exhaust shutter failed and the engine overheated. Replaced the broken exhaust shutter and the impeller and it’s housing. Boat started fine on the muffs. Went to the lake today and it ran fine for a half hour then slowly lost power and died. Was running a little warmer that usual, but not overheating. Just pulled the spark plugs and all are in the same condition. They appear to have overheated but were otherwise dry and in good shape. Compression was 0-0-30-90. Clearly I have a problem. Any suggestions on where to start? I’m thinking it may have reached the end of the road.

 

[QBhoy]

Cylinder head fried, best case. Very unusual to have 0 compression, even on a total right off engine. I’d suspect that the cylinder head is passing and not holding compression...or your valves are sticking open.

 

[Rick Stephens]

Pull the valve cover and look.

Missing exhaust shutters won't overheat an engine - an overheated engine will fry shutters. And water pocket. And head.

 

[kenny nunez]

It appears the head gasket is blown out, that does not mean the engine is hurt, It may just need a valve job and the head milled. If the cylinders are not scored it will probably live longer.

 

[boozer1966]

Thanks for the input, everyone. I ran a compression test again. Same result, even after squirting some oil in the cylinders. I thought if it was a problem with the rings that would show up by doing this. Also took valve cover off and turned the engine over. All the valves seem to be functioning ok. I took the head off to look at the head gasket, and it appears to be in good shape too. Cylinders don’t have any obvious scoring and pistons look good. I will post pictures.

My thoughts are to have the head looked at, find out why it overheated, put it back together and see what happens. Impeller was brand new.

Any other ideas?

 

[tank1949]

Thanks for the input, everyone. I ran a compression test again. Same result, even after squirting some oil in the cylinders. I thought if it was a problem with the rings that would show up by doing this. Also took valve cover off and turned the engine over. All the valves seem to be functioning ok. I took the head off to look at the head gasket, and it appears to be in good shape too. Cylinders don’t have any obvious scoring and pistons look good. I will post pictures.

My thoughts are to have the head looked at, find out why it overheated, put it back together and see what happens. Impeller was brand new.

Any other ideas?

To have 0 compression means something is really destroyed, usually a hole or valve. But first, check compression tester's air valve or tester on another engine to establish a base line. You may have experienced what I had decades ago: a defective tester. Water over damn now, but at least you will know. I also had a plastic bag wrap around an Alpha drive one time that pegged my temp needle. I now always have audio alarms in addition to gauges. It doesn't take long to seize a motor.

 

[boozer1966]

I’ve used the compression gauge on this and other vehicles. I’m pretty sure it’s not the gauge, but that thought did cross my mind. Thanks for the response.

 

[QBhoy]

Either the head has gone with trying to compress water and or those two units with the signs of water on the valves have the valves not sealing. One or both of them will be your issue.

 

[Scott Danforth]

Holy tulip'd valves

not only did you over-heat the head, you severely overheated it.

take the head to a machine shop and see if it can be salvaged.

 

[boozer1966]

Head was cracked beyond repair. Found a remanufactured head for a good price.