Closed system problems on a big block

I have been fishing in a Novi for a year or so. It has a mercruiser 454 and half the system is closed. We serviced the exchanger for the block and issues have arisen. Seems on shutdown and perhaps while we are running we are losing fresh water. No signs of loss in the bilge area. Runs at 165 temp hard no problem. This morning we started our day 10 miles out and no start. Wouldn't turn over. I was thinking thermal lock but checked that last. Sure enough some cylinders full of water. We had a tow back in and tomorrow will be taking it apart a little. I wonder if the exchanger might have been compromised during the cleaning or if we need to look to the risers for the answer. Help appreciated.

8122pbrainard wrote: Jack, With a half fresh water system, the manifolds are still cooled by raw water so, it's not a problem with the heat exchanger. I feel you are on the correct path looking at the exhaust manifolds. Did they also acid clean the raw water side besides the fresh water side? If so, that may have caused some manifold damage?

Exhaust manifolds/mixers damage +1

But....exhaust damage wouldn't cause loss of fresh water unless heat exchanger is damaged too. I bet you cleaned out all that nice rust/scale that was blocking your salt damaged exchanger and mixer holes. - Those holes are nice, clean and open now.

A leak-down test would help you feel better about the block AND $800.00-$1,000.00 exchanger.

Which cylinders were found to have water?
I think at this point your possibilities to the source of that water are...
-riser gaskets
-exhaust manifold
-head gasket
-cracked block
-cracked head

Last three could be checked with pressure check of closed loop I believe although there are more familiar people on this but me. Let’s hope it’s in the exhaust though...
Salt Life!

How about gasket damage from over heat at the riser /manifold intersection Steve, perhaps the fresh water loss was there? Fresh water in the manifolds and raw water in the risers could have mixed and exited?

Gary S wrote: Jack I have been told risers only last about 5 years in the salt fyi

We were told 2 years Gary. They certainly don't last long and these ones were bad. Boat came from Maine a couple years back. Have been replacing hoses and other stuff as needed and trying not to get broke down. Sometimes we are out 40 miles and too deep to anchor and a problem in the Gulf Stream could send us up to the carolinas LOL. We had a leak on an oil line out there that almost did just that till I made a nice speedy repair with a coors beer can, some 5200 and a couple radiator clamps. Repair was so good that we stayed and got our fishing in before returning home. Not sure a Busch can would have worked as well.

That's why I went with the Hi Teks. Dad flushed his after each run,got 7 years on the first set,5 on the second and sold the boat before the 3rd set needed to be changed. Every two years helps justify the price Jack. Is the Novi a I/O ?

I don't remember a lot of things.

8122pbrainard wrote: juniorwoody wrote: a mercruiser 454 and half the system is closed. juniorwoody wrote: Since the manifolds are cooled by the closed system we hope they are ok. Jack, Are you sure regarding the manifolds? You mentioned a half system first but then a full system later where the manifolds are also fresh water cooled. Half system: Just to be safe, maybe the manifolds should be pressure checked too?

I was wrong full system. Manifolds cooled by closed loop.