cracked block headgasket or something minor?

[skinwalker]

454 MPI Mercruiser MAGNUM motor

drove my boat at WOT yesterday for a few minutes. I just bought the boat and do not know its history. Suddenly started hearing a ticking and knocking noise in the engine and experienced power loss. I see alot of white vapor coming out of the exhaust, i notice the driver side exhaust manifold is hotter to the touch than the other side. Not sure where to begin... or what happened. Also the oil was below the add line (noticed that like a idiot AFTER the knocking noise). I bought a compression tester kit but looks extremely challenging to get to the plugs and not sure what to disconnect and where prior to starting that test. I am only mildly mechanical ...however do well with youtube videos and instructions. I paid ALOT of money for this stupid boat assuming it was reliable, it ran the day before GREAT... any advice would be very helpful. I also took a video of it running

also boat is not overheating

 

[alldodge]

Sorry to hear your troubles, but with white smoke out the exhaust, my guess is you blew a head gasket. A compression test will verify.

Could use a motor serial number to verify components

One exhaust side will always be a bit hotter then the other, but neither should burn to the touch

Label all the plug wires before you start. Can use some masking tape or similar.
Remove all of the plugs
Disconnect the connectors (item 17) from the coil (item 18)
https://www.mercruiserparts.com/bam/subassembly/31810/2336/7

Move the throttle handle to WOT, throttle only mode
install the gauge in one of the spark plug holes
Crank motor over 5 times and write down reading

Remove gauge from cylinder and install in next spark plug hole and repeat until all done

In the future, right after you buy a boat, do all maintenance, even if the guy says I just did that.
New impeller
Oil change
Engine alignment
Replace fuel filters
remove distributor cap inspect and/or replace
Remove spark plugs inspect and/or replace

 

[Bondo]

I just bought the boat and do not know its history.

Ayuh,..... Just a WAGuess,..... The fuel filter is 1/2 full of water, the lean condition caused detonation(the clicking noise), you kept pourin' the coal to it, 'n the detonation either burnt a piston, hammered a rod bearin', 'n possibly blew a head gasket,......

1 exhaust manifold or the other will be warmer, they're rarely to never the same,.....

'n Ya, gettin' the spark plugs out might be abit of a chore, but that's the textbook definition of "Workin' on a boat",.....

The compression test, should tell the story,.....

 

[Scott Danforth]

rarely does the head gasket go....its usually something a bit more catastrophic.

do a compression test, and if any pressure values are lower than 10% of the highest value, do a leak down test.. BTW, compression on a good motor is in the 140-150psi range.

 

[Rick Stephens]

New to you boat means all the maintenance should be done before taking it out. Your story is not unusual.There's several threads going right with various issues that good post purchase maintenance should have resolved. Sorry to say your work is cut out for you. As a note - I bought my first boat without having much more than a minor clue what I should REALLY be looking for. Mostly I lucked out, however there were some maintenance dead giveaways that I missed, and the seller went out of his way to poo poo, that cost me some change all those years back. I let a purty boat sway my evaluation.

Anyway, time to get dirty. Any questions, the above gentlemen who posted on your thread have done it all so many times, they are the real experts here.

 

[skinwalker]

rarely does the head gasket go....its usually something a bit more catastrophic.

do a compression test, and if any pressure values are lower than 10% of the highest value, do a leak down test.. BTW, compression on a good motor is in the 140-150psi range.

compression test shows all cylinders between 130-140 psi. I did not have throttle WOT when i tested

 

[skinwalker]

Ayuh,..... Just a WAGuess,..... The fuel filter is 1/2 full of water, the lean condition caused detonation(the clicking noise), you kept pourin' the coal to it, 'n the detonation either burnt a piston, hammered a rod bearin', 'n possibly blew a head gasket,......

1 exhaust manifold or the other will be warmer, they're rarely to never the same,.....

'n Ya, gettin' the spark plugs out might be abit of a chore, but that's the textbook definition of "Workin' on a boat",.....

The compression test, should tell the story,.....

should i remove the fuel filter? also remove oil filter and pour into a clear glass looking for metal? My thoughts are a broken valve spring or a bad exhaust manifold. Not sure how to isolate problem.

 

[skinwalker]

oil sample appears free of any debris or metal. appearance of coffee color with normal oil viscosity.

 

[alldodge]

Empty fuel filter to look for water and anything else but clean gas

Dumping the oil filter will do nothing in most cases. If you cut the filter open and look thru it for metal then maybe

If you have knocking, the motor needs to be rebuilt. It either spun a bearing or bend a rod

 

[QBhoy]

Were the plugs damp ?

 

[Scott Danforth]

if the compression numbers were good on all cylinders, that rules out head gasket

do a cooling system pressure test