Oh crap!!

Dave 1964

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I bought this 1976 Mercruiser 120 after a closer inspection of the boat I found what I think is the former owners way to fix a problem. What is your opinion on this gray stuff around the head in this picture
 

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GA_Boater

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It looks like rust is making it's way through the crud. Judging by the amount of crack fixer used, the manifold is shot.
 

Dave 1964

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Yes the oil is a little milkie I also found a freeze plug down by the bilge pump. It's not damaged at all it just blew out or fell out
 

Grub54891

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Looks like she's been froze, more than once. With any real luck, it may not be totally cracked, but that manifold will need to be replaced. I'd start with a cooling system pressure check, compression, and leakdown tests. I have a 120 and a 140, both were froze but survived by just blowing out the core plugs, got them cheap and are good runners. The 120 gets slightly milky when just idling slowly watching the scenery, but a good ten minute run at wot she clears up. It could be a leak, but passes all my above mentioned tests. I think its condensation from running cool lake superior water, thought about switching from the 140 deg thermostat, but am reluctant to do that.
 
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Bt Doctur

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And you will know the block condition once you remove the manifold
 

gm280

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WOW Dave 1964, I hate to say it, but I have to concur with the above posters. I think it did freeze as well. And before spending even a dime on it. I would plug up the cooling system from teh pick up to the output, and then use a hand pump at a "T" in hose area and pump it up to about ten pounds and check it over real well. Either way, I see that engine coming out for a good cleaning and going over really well. And that includes the manifold and maybe even the heads. JMHO
 

bman440440

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Looks like she's been froze, more than once. With any real luck, it may not be totally cracked, but that manifold will need to be replaced. I'd start with a cooling system pressure check, compression, and leakdown tests. I have a 120 and a 140, both were froze but survived by just blowing out the core plugs, got them cheap and are good runners. The 120 gets slightly milky when just idling slowly watching the scenery, but a good ten minute run at wot she clears up. It could be a leak, but passes all my above mentioned tests. I think its condensation from running cool lake superior water, thought about switching from the 140 deg thermostat, but am reluctant to do that.

I would run a 160 thermostat in that... IMO it will take care of that issue... you need to get that block nice and warm to burn off the condensation
 

Grub54891

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I would run a 160 thermostat in that... IMO it will take care of that issue... you need to get that block nice and warm to burn off the condensation

​Yeah, I was thinking the same thing. condensation. Thanks!
 

Bondo

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How do you do a cooling system pressure check

Ayuh,.... Ya need to drain the block, isolate the block, from the rest of the coolin' system, no manifolds, 'n pressurize with air to 'bout 10/ 15 psi, 'n Listen,....

If it's cracked, you'll hear it,...
If not, it'll hold pressure,...
 

Dave 1964

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Well I performed an easy test today on it and hate the results. I did a compression check. on cld#1 125psi cld#2 15psi. Cld#3 about 8psi Cld#4 125psi. I did the compression check after I put the freeze plug back in
 

Grub54891

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That could be just bad valves, rings, or gasket, did you do a wet test also? Looks like a haeadgasket but a crack would do that also.
 

Bt Doctur

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remove the spark plugs, drain the oil and leave the drain plug out
remove raw water inlet hose from therm housing and make an attachment for a short hose with a hose fitting to attack a garden hose
turn on full water pressure and look for water leaving the oil pan or sparkplug holes
 

Dave 1964

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Wouldn't that have the same result for blown gasket or a bent valve. I already know something is wrong because barly any compression on # 2&3
 

Grub54891

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By wet test I meant compression. You already did the compression test, now squirt a pump or 2 of oil in the cylinder, and check compression again. If the numbers go up, you have bad rings, if they stay close to the same, you have bad valves. in your case, it may be a head gasket or crack in the block also. A wet test will help you diagnosing any issues, or at least give you a better idea of what's doing on.
 
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