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1967 Merc 60 cooling system keeps clogging.

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Ineptus_Mechanicus

New member
As the title says, I have a 1967 Merc 60 6hp unit I'm repairing. I've replaced the water pump and a few of the lower unit seals and its oil, all that seems to be working fine - but the cooling system keeps clogging with sand and rust debris. It'll push plenty of water for about 30 seconds, then it'll slowly taper off to almost nothing and I'll have to get the airgun out, remove the flush plug, and blow more crap out of it. It pushes water fine for another 30 seconds, rinse and repeat. I'm getting real tired of doing this, so if anyone has an idea on how to fix this permanently that'd be great.
 
Great little motor, just needs some TLC. Have you removed the cylinder water cover and inspected the water passage around the cylinders? It may be loaded with scale, sand and debris. You may be temporarily dislodging it when blow with compressed air, then it replugs once you start pumping water again. Another possible cause is a bad exhaust gasket that is allowing exhaust gasses to interfere with the normal exiting water flow and holding water back. I'm assuming you are realizing this issue in a clean test tank, clean water and the gearcase well submerged 6-8" above the cavitation plate.
 
fitz73222 said:
Great little motor, just needs some TLC. Have you removed the cylinder water cover and inspected the water passage around the cylinders? It may be loaded with scale, sand and debris. You may be temporarily dislodging it when blow with compressed air, then it replugs once you start pumping water again. Another possible cause is a bad exhaust gasket that is allowing exhaust gasses to interfere with the normal exiting water flow and holding water back. I'm assuming you are realizing this issue in a clean test tank, clean water and the gearcase well submerged 6-8" above the cavitation plate.
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Running in a clean-ish tank, it's starting to get a bit greasy because I haven't changed the water in a week or so.

Nope, haven't removed the water cover yet - I'm coming into this blind, with only one youtube video to guide me on the repairs (and nothing you mentioned was covered in said video). The exhaust gasket sounds like it might be my problem here, to be honest. I have exactly zero water coming out of the exhaust relief port under the powerhead, which I already know isn't normal. I'll see what I can do, thanks for the advice.
 
Ineptus_Mechanicus said:
Running in a clean-ish tank, it's starting to get a bit greasy because I haven't changed the water in a week or so.

Nope, haven't removed the water cover yet - I'm coming into this blind, with only one youtube video to guide me on the repairs (and nothing you mentioned was covered in said video). The exhaust gasket sounds like it might be my problem here, to be honest. I have exactly zero water coming out of the exhaust relief port under the powerhead, which I already know isn't normal. I'll see what I can do, thanks for the advice.
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I don't know the serial number for your engine, but does it have that apex shaped plate with a dozen or so screws that is underneath the bottom cylinder in the engine pan? If not mistaken that also scavenges the dry exhaust with cooling water that comes out of the exhaust relief port, it's like a maze of passages underneath that plate, I've seen those carboned up and plugged with gunk. Is the engine actually running hot?
 
fitz73222 said:
I don't know the serial number for your engine, but does it have that apex shaped plate with a dozen or so screws that is underneath the bottom cylinder in the engine pan? If not mistaken that also scavenges the dry exhaust with cooling water that comes out of the exhaust relief port, it's like a maze of passages underneath that plate, I've seen those carboned up and plugged with gunk. Is the engine actually running hot?
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I have no idea if it's running hot, personally. I don't actually know what temp these are supposed to run at, come to think of it. I've always stopped it pretty soon after it stopped flowing what I thought was enough water to cool it, though the water that WAS coming out was fairly warm, so I assume it was doing something to cool the engine. I don't even know where to start with disassembling the top end of this thing - seems like everything is attached to everything else.

Looks like this site doesn't support images that are over 1mb in size so I've attached them as links, except for the serial number pic which is garbage enough quality that it doesn't hit the limit.

https://media.discordapp.net/attach...4814/20230727_124311.jpg?width=827&height=465
https://media.discordapp.net/attach...1712/20230727_124304.jpg?width=827&height=465

merc3.jpg
 
Your engine is the later style 6, no flat plate in the rear lower cowling, disregard discussion regarding it. when you replaced the impeller was it intact?, or missing vanes (fins) should have been 6 if the impeller was intact.
 
fitz73222 said:
Your engine is the later style 6, no flat plate in the rear lower cowling, disregard discussion regarding it. when you replaced the impeller was it intact?, or missing vanes (fins) should have been 6 if the impeller was intact.
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Oh, no, it was pretty much a circle. I did make sure to blow air through the water exhaust when I had the lower unit off so that any chunks would hopefully get blown out of the pickup tube.
 
Unfortunately, you may have to dig deeper into this from pieces of impeller being lodged up in the water tube or powerhead base if the things are clean after removing the cylinder water cover and you still have the problem.
 
fitz73222 said:
Unfortunately, you may have to dig deeper into this from pieces of impeller being lodged up in the water tube or powerhead base if the things are clean after removing the cylinder water cover and you still have the problem.
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Since I couldn't find any pictures of one - what part of this is the water cover?
 
fitz73222 said:
Part number 25 on the breakdown

Mercury Marine 60 Cylinder Block & Crankcase Assembly Parts

Mercury Marine 60 cylinder block and crankcase assembly parts. Buy a genuine Mercury Quicksilver or aftermarket part.
www.marineengine.com www.marineengine.com
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Thanks a bunch! Didn't know the exploded view was publicly available. I might take the exhaust cover off to clean inside there as well, as I was told by the previous owner that this motor was used almost exclusively at idle speeds and I imagine there's a fair bit of soot in there.
 
Ineptus_Mechanicus said:
Thanks a bunch! Didn't know the exploded view was publicly available. I might take the exhaust cover off to clean inside there as well, as I was told by the previous owner that this motor was used almost exclusively at idle speeds and I imagine there's a fair bit of soot in there.
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Perfect, now we need to work through removing exhaust cover bolts without breaking them! Patience Grasshopper!
 
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