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Clogged up cooling jacket? Cannot drain block.

9

91stingray

Contributing Member
I was in the process of winterizing my carbureted and raw water cooled 7.4 and my coolant passesges near the drain plugs are so clogged up I can only get one side to drip a bit. I was at it for hours with picks, stiff wire, and compressed air, I also tried running the engine with the plugs out and got nothing. It never gave me any issues running hot. My temps read in the 145-150 range. Besides not being able to winterize properly, is this something to be concerned about regarding the engine not cooling properly? I figure I can probably run it until it needs rebuilt and at that point have the block totally torn down and cleaned and resurfaced.
 
You could:
make a tool from a 1/4 inch brass nipple, coupling, and air chuck fitting. Screw into the block and add hi pressure air to try and blow it loose, Then hook up a water source, and do fills and drains until clear.
 
That’s one of the drawbacks of raw water cooling, even if it’s not rust it can be sand. Depending on access I wonder if you can remove a casting plug and use some stiff wire in a drill to loosen up whatever’s in there.
 
louc said:
That’s one of the drawbacks of raw water cooling, even if it’s not rust it can be sand. Depending on access I wonder if you can remove a casting plug and use some stiff wire in a drill to loosen up whatever’s in there.
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That what my buddy who's a mechanic suggested. I'm wondering if there's some kind of chemicals I can circulate through the system that could help break it up a bit.
 
Bt Doctur said:
You could:
make a tool from a 1/4 inch brass nipple, coupling, and air chuck fitting. Screw into the block and add hi pressure air to try and blow it loose, Then hook up a water source, and do fills and drains until clear.
Click to expand...
I was thinking something similar that I could make to shoot pressurized water in as well.
 
I would try what Boat Dr suggested first, that’s the least invasive method and could work. The other thing that might work is to find out what resto shops use to dissolve rust in blocks they are restoring; you might have to fill it and let it sit a while but be careful because all those rust solvents are toxic and most are flammable. Expensive too you’d need several gallons.
On my old 1988 4.3 when I winterize it I drain the motor and always dig out the drain holes with a pick, that has prevented mine from totally clogging up. 22 years raw water cooled in salt water. When I repower this boat 2 must haves are closed cooling and a remote oil filter mount.
 
This is one of the problems of trying to make draining easier- it usually doesn't work. First, the blue plastic plugs are too soft and cross-thread very easily, even if someone is careful. They should be brass or more durable plastic. Then, the fitting used for the plugs prevents debris moving out if the area. Using a wire to chase the debris is necessary and if sand has collected, it's because the boat was run through sandy water or literally through sand.
 
louc said:
I would try what Boat Dr suggested first, that’s the least invasive method and could work. The other thing that might work is to find out what resto shops use to dissolve rust in blocks they are restoring; you might have to fill it and let it sit a while but be careful because all those rust solvents are toxic and most are flammable. Expensive too you’d need several gallons.
On my old 1988 4.3 when I winterize it I drain the motor and always dig out the drain holes with a pick, that has prevented mine from totally clogging up. 22 years raw water cooled in salt water. When I repower this boat 2 must haves are closed cooling and a remote oil filter mount.
Click to expand...

If the engine still runs well and doesn't have damage from salt, why not add the parts for a closed cooling system?

Everything I have heard about using a boat in salt water makes me not want to.
 
The issue is the way cast iron corrodes. Unlike aluminum it flakes off. After about 100 or so hrs the flakes can clog the heat exchanger and cause overheating. So the time to do it is with a new or remanufactured engine.
Don’t fear salt water. It is better in a few important ways. For one which is a big one we never have issues with low water due to droughts. We always have plenty of deep water. For another if you have an older wood cored boat, salt water doesn’t rot transoms like fresh water does. And being on an island like I am it gives me the widest range of boating venues you can have. I live 300 ft from the water that leads out to two major bays and Long Island Sound. So, I just do the extra maintenance that comes with it. Manifolds/elbows every 7 seasons. Trailer has to be alu or galvanized no painted trailers. Brakes, I use galvanized drums. My boat is on a mooring so the trailer doesn’t get much exposure to salt. BTW, the short block in my engine has 22 years in salt water. I changed the cyl heads 7 years ago.
 
If you do have the Blue plugs the brass insert must be removed first to screw into the block. block threads are 1/4 pipe . there should also be 2 core plugs in the front of the motor.One on each side. You could try going inside from there
 
Bt Doctur said:
If you do have the Blue plugs the brass insert must be removed first to screw into the block. block threads are 1/4 pipe . there should also be 2 core plugs in the front of the motor.One on each side. You could try going inside from there
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I removed the metal drain plugs completely, no plastic plugs. I removed them from where they thread into the block and dug around with picks and coat hanger metal for a few hours. After a while I couldn't tell if I was hitting metal or if the stuff in the cooling jacket is completely solidified.
 
Bt Doctur said:
If you do have the Blue plugs the brass insert must be removed first to screw into the block. block threads are 1/4 pipe . there should also be 2 core plugs in the front of the motor.One on each side. You could try going inside from there
Click to expand...
this is probably the best bet given what has been mentioned and potential to lose a engine over it. If you can knock them in and pull out with channel locks you can replace with a rubber expansion plug. you should be able to dig it out. or get a stream of water in there and work it out
 
louc said:
The issue is the way cast iron corrodes. Unlike aluminum it flakes off. After about 100 or so hrs the flakes can clog the heat exchanger and cause overheating. So the time to do it is with a new or remanufactured engine.
Don’t fear salt water. It is better in a few important ways. For one which is a big one we never have issues with low water due to droughts. We always have plenty of deep water. For another if you have an older wood cored boat, salt water doesn’t rot transoms like fresh water does. And being on an island like I am it gives me the widest range of boating venues you can have. I live 300 ft from the water that leads out to two major bays and Long Island Sound. So, I just do the extra maintenance that comes with it. Manifolds/elbows every 7 seasons. Trailer has to be alu or galvanized no painted trailers. Brakes, I use galvanized drums. My boat is on a mooring so the trailer doesn’t get much exposure to salt. BTW, the short block in my engine has 22 years in salt water. I changed the cyl heads 7 years ago.
Click to expand...
I know cast iron corrodes and that it flakes- I have serviced many,. many boats- it does that in fresh, brackish and salt water but low water is only a problem on lakes and rivers, or when the boater doesn't know the local conditions or pay attention to their maps/depth finder- I live two miles from Lake Michigan and it's still possible to run aground because the wind/storms change the level but we don't actually have tides like oceans do.
 
I think that the basic issue is that GM did not design these engines to be raw water cooled, and with the drain plugs at the lowest part of the block some will clog inevitably. Larger drains, or even easily removable core plugs, would have been a good option to avoid losing an engine over something like that.
I would not put a closed system on a well used salt water boat due to the flaking, it will for sure clog the heat exchanger, pretty much every marine mechanic around here will tell you that. However, if I do repower it, then yes for sure I will add at least a half system. That and I want to see if I can adapt the Merc dry joint exhaust system to my OMC engine, I feel it is a better design.
 
Half vs full FWC.... a penny pinching way to reduce cost of a FWC... smaller Heat exchanger and possibly smaller RW pump. Dry joint elbows require a MERC dry joint manifold.
 
The idea of the half system is the standard raw water impeller might not move enough water to do a full system. Now if someone could tell me that it would definitely work with the impeller I have then for sure I’d want a full system. I have heard of people adding an engine driven pump to adequately feed a full system.
 
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