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Fresh water cooling question


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I have a question for the mechanics out there  I recently bought a 1994 1830 sport with a 4.3 MerCruiser  with a fresh water cooling system on it. And I am finding more every day that the person I bought it from was not completely up front about a few things or just did not know what he was doing he .....told me that he bought the boat and found that the block was cracked and that he got a new block and by new block I believe he means new to this boat ..... he and a friend that is supposed to know about boat motors rebuilt it .... he said they put it in the water and ran it for a short period of time and that it was running rough and needed to have the timing set..... I myself am new to boating and know nothing about the cooling system but am learning as I go.... so in the process of finding the reason the boat was missing ......was a broken rocker arm stud ..... i had to take the riser off the one side to work on the valve train and after I put the motor back together and running it I noticed I could not keep coolant in the fresh water system it would all run out the exhaust so in a panic I thought it might have a cracked head but after doing every thing I could to prove that to be right I came to the conclusion that it was not a head or cracked block so I started checking into the cooling system to see if they connected a hose wrong . I ran across a video on how to add a fresh water system to a boat that did not have one and one of the steps was putting in the restrictive plate between the exhaust Manifold and riser at that point I realized that there were no restrictor  plates on this motor. My question is does the factory mercruser cooling system require them it is possible he took the exhaust off one that had no cooling system on it . From what I can tell without the restrictor the fresh water coolest will just run into the riser and out the exhaust any help would be appreciated 

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1 hour ago, Beede19941830 said:

Thought so I just wanted to make sure all cooling systems worked that way before I block it off

I would also pressure test the tube to shell heat ex-changer as it has raw water on the tube side, and engine coolant on the shell side. A failed tube or leaking tube sheet will allow coolant to drain into the raw water side of the system,. Simple air test will eliminate that unit as a possibility. Per Merc OEM manual #32, no engine coolant enters the jacketed exhaust manifolds or risers, only raw water. Engine coolant circulation is limited to block, heads, intake manifold, heat ex-changer, thermostat housing, and engine coolant circulation pump. Coolant entering the raw water system can only be from a failed ex-changer, cracked block, or cylinder head as you suspect. My money is on a leaking ex-changer. If you find a single tube leak, you can plug that tube (both ends) with a tapered brass plug on a 4.3 as the ex-changer is bigger than it needs to be. Two leaking tubes and it's time to find a replacement. W

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tried to do a pressure test but with the ports open directly into the risers it would build no pressure at all so I will get the new gaskets to separate the exhaust manifold from the riser and then try a pressure test again ..... I believe that the previous owner when rebuilding the motor put the exhaust system from the motor without the fresh water system on the mother that had the fresh water system and did not know about having to have the restrictor plates in them ..... explains alot

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4 hours ago, Wingnut said:

I would also pressure test the tube to shell heat ex-changer as it has raw water on the tube side, and engine coolant on the shell side. A failed tube or leaking tube sheet will allow coolant to drain into the raw water side of the system,. Simple air test will eliminate that unit as a possibility. Per Merc OEM manual #32, no engine coolant enters the jacketed exhaust manifolds or risers, only raw water. Engine coolant circulation is limited to block, heads, intake manifold, heat ex-changer, thermostat housing, and engine coolant circulation pump. Coolant entering the raw water system can only be from a failed ex-changer, cracked block, or cylinder head as you suspect. My money is on a leaking ex-changer. If you find a single tube leak, you can plug that tube (both ends) with a tapered brass plug on a 4.3 as the ex-changer is bigger than it needs to be. Two leaking tubes and it's time to find a replacement. W

If it does not enter the exhaust manifold then why the restrictor plate between the manifold and riser

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12 minutes ago, Beede19941830 said:

If it does not enter the exhaust manifold then why the restrictor plate between the manifold and riser

The restrictor as you refer to it is an anti-reversion plate that helps prevent water-laden exhaust gasses from back flowing into the manifold, and exhaust valve port during heavy deceleration. To test the integrity of your water to water heat exchanger, remove the closed loop cooling water lines from the exchanger shell (antifreeze side) cap the outlet, and apply a 5# air pressure to the inlet. If it leaks into the raw water side (tube side of the exchanger) then the exchanger has failed. There is no difference in part numbers between the fresh water cooled (closed loop) and raw water cooled 4.3 engine exhaust manifolds. A fresh water cooled 4.3 is a bit rare. There is no antifreeze that enters the exhaust manifolds, only raw sea water. If your antifreeze bottle is going empty, look elsewhere. W

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so there are two different fresh water cooling systems it appears .....one as you stated the fresh water never enters the exhaust manifolds it only runs trough the block and the heads and for that system you do not use the plates that block off the manifold and riser so the raw water flows trough both and out the risers..... the second system the fresh water flows trough the block and heads and also trough the exhaust manifold and then back into the cooler for this system the manifold and the risers are not connected to each other the plate that i am talking about keeps the water in the exhaust manifold water jackets from entering into the water jacket in the risers .....the flow going into the risers comes from the cooler ......check out this diagram it will show both ......the system on my boat is for the most part the top diagram except the manifold has the standard gaskets 

 

 https://www.perfprotech.com/blog/articles/fresh-water-cooling-full-system

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Hello again Beede. You have a strange bird indeed. I can find no reference where Merc ever installed closed loop manifolds on an I/O installation back in 1994, only inboards, and even then those applications were quite limited. Perhaps your engine cam from a donor boat that had inboards or was built after 1999. In any case, you can decide now if you wish antifreeze jacketed manifolds, or go with the more conventional sea water jacketed configuration. Same manifolds, different plumbing. Sorry I sent you down the wrong path for a time, but I have never seen closed loop manifolds on an I/O before the 1999 model offerings as the earlier heat exchanges on those tend to be smaller than their inboard counterparts, and can't handle the extra heat load. It would be interesting to know how big your supplied heat exchanger actually is. Likely you have the newer 1999 on up engine as depicted below.        W

 

http://www.marinepartsplus.com/catalog/mercruiser/serialize(value)/4.3L_CARB_ALPHA-BRAVO/884714004/13798-190

http://www.marinepartsplus.com/catalog/mercruiser/serialize(value)/4.3L_CARB_ALPHA-BRAVO/884714004/13798-160

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the heat exchanger is a mercuries brand i will look and see if it has a model number the boat also picks up the water from the bottom of the hull instead of picking it up from the out drive ......in the mean time do you know if the windshield on the1994 1830ss sport is the same glass that was on the 1992 2000 sl sport   

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