Closed loop cooling, sediment around thermostat…

bigblock454

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Good evening all. Purchased a 1986 Wellcraft 2900 Sportbridge, with dual mercruiser 350cid inboards. Each has a heat exchanger mounted on it. Rebuilding the heat exchangers now, and they look fine. But I am a bit alarmed at this yellow/green sediment under the thermostat, darn near clogging that area up. The boat has been sitting for a few years. Is this common? Thank you for any and all advice.F516E49C-B2BF-4C2F-8AA3-F71F583B001B.jpeg
 

bigblock454

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Again, heat exchanger and their tubes are pretty clean. The thermostats are rated at 140°. In the process of cleaning the heat exchangers, replacing and gaskets and anodes. Thanks for any help and/or advice, regarding that yellow/green sediment.
 

Eric 3.7LX Alpha 1

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What that kind of build up it looks like it wasn't always closed cooling. Looks like mineral build up. I wonder how Barnacle Buster would do to clean that up.
 

bigblock454

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Me again… just to add… The hoses are in great shape, and has good looking antifreeze in it, currently. Just puzzled by the blockage under the thermostats, particularly the bypass area. There is a brass ring in the thermostat risers, that I am going to attempt to replace. Those brass rings look as if someone tried to remove them with a chisel at one point, and gave up. Either that, or they used a chisel to expand those brass rings in place. Not sure what they were trying to do, but I want to correct it. Thanks again.

Norm
 

bigblock454

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Thank you for your quick reply. It is the build up, seen in the picture. Kind of gooey, when wet, but quickly turns to dust as it dries. As far as I know, this boat has always been close loop. Thanks again.
 

bigblock454

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Barnacle buster sounds like a good idea to run through it, when it is buttoned back up. Again, everything else seems to look pretty clear of sediment and debris. Just that area underneath the thermostats. Puzzled.
 

bigblock454

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135F69DF-8FF2-424E-AD01-68A35E8A0FF3.jpgBD377D07-7CE7-4618-B4D0-9E6502EC8827.jpegF092FBE4-AA0D-456E-8B39-D28CB009C59D.jpeg31D33B7B-E3B3-4F35-B031-B4F450711F7B.jpg0593DFE6-41C3-4682-82A1-68AE04B14956.jpeg
Few more pics. Hope they come through in order, as I am doing this from my cell phone. First one shows the brass rings inside each thermostat riser/housing. Looks like someone either tried to remove them, or install them with a chisel! Mind you this was all closed up and running like this. Don’t know if that added to the sediment buildup or not. Then, pictures of the removed rings, as I am going to replace Them. Also shown or the housings without rings in them, and the two heat exchangers apart, being reconditioned. Still not sure what would cause this green slime/sediment, and a closed loop system. Boat always had closed it/freshwater cooling. Thanks again for any advice.
Norm
 

bigblock454

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Also attached picture above of thermostat, showing another view, how sediment accumulation was confined to underneath the thermostat, in the riser area. I have a theory, but I am not an expert on the situation. Have to go back to work, for the second half of my day. I will check back later, and post my theory. Interested if anyone else has expertise on this. Thank you.

Norm
 

bigblock454

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Ok… on break again. So…. My theory (and I could be way wrong): if you look at the riser, that the thermostat sits on, it has a bypass cut into it, that to me looks rather large. To support this “theory”, I see now that they offer gaskets reducing the size of that bypass to a hole that seems to be about quarter inch in diameter, thereby restricting the bypass considerably. Wondering if this was done, because perhaps the bypass was working too good, and the thermostats weren’t opening up. Restricting them, would make thethermostats work as intended. I’m wondering if because the thermostats were seldom opening (if at all), if that created an area, susceptible to blockage, and sediment buildup. Interested in hearing some thoughts. Thanks for anybody that may be “listening“.

Norm
 

bigblock454

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Guess not much traffic on these website forums anymore. Seems everything has migrated, or is migrating to FB. Guess I need to break down, and make an account. Ugh

Norm
 

bigblock454

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In the process of doing lots on the boat. Was hoping to share and get some answers here. Perhaps if I put this, and the rest of my inquiries as well as progress on the “resto“ page?

Norm
 

Eric 3.7LX Alpha 1

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Well you did a good job cleaning it up.

Do you have the service manual for the engine? I think it would be manual #9 which covers GM V-8 engines from '85-88. It says the closed cooling system should be drained and inspected every two years, as well as the seawater section of the heat exchanger or whenever decreased cooling efficiency is suspected. It sounds like build up is possible and should be cleaned like your doing if it occurs.
 

achris

More fish than mountain goat
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I second Eric's comment about the engines not always being close cooled. The fact that they have 140° thermostats sort of backs that up. Part of the closed cooling kit (when it's installed on a new engine) is a 160° thermostat. If they were closed cooled from new, they'd have had 160° thermostats.

Chris....
 

Scott Danforth

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Agree with the enginea not always being closed cooled. Looks like they alao cheaped out on the antifreeze
 

bigblock454

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Wow! Certainly appreciate your replies and help. I’m certainly no expert, and that’s why I am posting here. From what research I have done, to find replacement parts, it seems that “that” particular thermostat riser and housing is only available on closed loop design.. Rall water thermostat riser looks quite different. Just wondering why if changing from raw water, to close loop, why someone would replace all the parts (riser, housing), etc. but keep the same thermostats, especially if they were fouled with sediment. Am I making any sense with that? Again, not to argue, but just debate and learn. Those are (I’m pretty sure) closed loop system thermostat housings, that are clogged up. Previous owner is stating that it was always closed loop, and the option sheet for that boat model has it as an option for that year. But, obviously I did not buy it new, so I would not know for sure. But again, raw water cooled housings look quite different. Was thinking “cheap” antifreeze could certainly have something to do with it, as well as perhaps using regular tap water. Anyway, I’m going through the whole thing, cleaning it out. The barnacle buster seems to be the way to go. Thank you again for your kind help and direction.

Norm
 
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