Cracked Block or Bad Riser?

[reierme]

Last winter I failed to properly winterize my boat. Doesn't typically get cold where I live but last winter was unusually cold. I went to prep my boat for it's first outing and noticed water shoot out of my manifolds. After some inspection, I noticed the cylinder heads were cracked as well. The oil was milky. So I purchased new cylinder heads and exhaust manifolds. I lapped the valves, did valve lash adjustment and tested compression. Cylinders 2,4,6, and 5 tested at 175psi and cylinders 1&3 were at 165psi and 170psi. I drained oil and added new oil. Idled boat for 5 minutes and drained oil again. I took the boat to the lake and idled around for about 20 minutes, shutting it down every 5 minutes to check oil level. After everything appeared ok, I ran it up to full speed and it ran great for about 5 minutes and then it shut down. The risers were hot and I noticed the gasket was leaking between riser and manifold. I installed new gasket set and have now decided to pressure test block. I capped hoses going to manifolds and disconnected coolant hose at outdrive where I pressure tested block. Pressure drops immediately and sounds like air is escaping thru riser as I can hear it at outdrive exhaust piping. Am I doing something wrong or is this an indication the riser is bad?

​Thanks

 

[kenny nunez]

Remove the hose that goes from the thermostat housing to the exhaust manifold and connect a garden hose to run water through the manifold and riser, there should be no back pressure as the water exits out the riser. Is the sea water pump in good condition ?

 

[Scott Danforth]

I would replace the manifolds and risers myself.

 

[reierme]

Manifolds are brand new. I can flow water thru manifold and riser with no backpressure. All water exits out the back of the boat freely. I'm going to replace risers since they are probably original to my 2003 boat. I'm not sure about the water pump. I was told by a mechanic that 9 times out of 10, if the head cracks due to freezing, so will the block. I need to confirm whether or not the block is cracked.

 

[alldodge]

was told by a mechanic that 9 times out of 10, if the head cracks due to freezing, so will the block

Pressure drops immediately and sounds like air is escaping thru riser

Also think your block is cracked

 

[reierme]

I capped hoses going to manifolds and disconnected coolant hose at outdrive where I pressure tested block. Pressure drops immediately and sounds like air is escaping thru riser as I can hear it at outdrive exhaust piping. Am I doing something wrong or is this an indication the riser is bad? Need help successfully pressure testing block.

 

[Scott Danforth]

Manifolds are brand new. I can flow water thru manifold and riser with no backpressure. All water exits out the back of the boat freely. I'm going to replace risers since they are probably original to my 2003 boat. I'm not sure about the water pump. I was told by a mechanic that 9 times out of 10, if the head cracks due to freezing, so will the block. I need to confirm whether or not the block is cracked.

the mechanic had it wrong, the blocks crack way easier than the heads, so if your heads cracked, your block was toast long before your heads cracked. its 9 times out of 10 if the block cracks, the heads crack

I capped hoses going to manifolds and disconnected coolant hose at outdrive where I pressure tested block. Pressure drops immediately and sounds like air is escaping thru riser as I can hear it at outdrive exhaust piping. Am I doing something wrong or is this an indication the riser is bad? Need help successfully pressure testing block.

if you have new manifolds and risers, and your line to the manifold is blocked off. there are two choices. you either have a cracked block and the air is most likely escaping thru an open exhaust valve into the exhaust system, or you have a failed head gasket. most likely your block is toast and you need a new short block to go with your heads

 

[alldodge]

I capped hoses going to manifolds and disconnected coolant hose at outdrive where I pressure tested block. Pressure drops immediately and sounds like air is escaping thru riser as I can hear it at outdrive exhaust piping. Am I doing something wrong or is this an indication the riser is bad? Need help successfully pressure testing block.

Don't see what size or year the motor is, but figuring its a V8 from the cylinder numbers listed. Its always good to know what your working on.

If you only have one water hose feeding the exhaust manifold then you have sealed off all exits. Pressurizing the intake hose should be all that is needed. So since your hearing air escape out the exhaust, you either have a block or head crack. The heads have been replaced so this only leaves the block, unless the heads used also had a crack

 

[capt.sam]

As for being an automotive machinist for 30years I have to agree with Scott and AllDodge.I have pressure tested many marine blocks and manifolds over the years and you never know for sure what the cause is until you find it. Pressure test everything.