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Old 22-05-2017, 20:25   #1
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mercruiser overheating - impeller good ??

Hi all, tryign to figure out whats happening.. have a 1967 mercruiser gm 120 with what looks like a pre alpha mr type outdrive.

Took the impeller off, it was in excellent shape, flexible and not cracked.

When we run it on the muffs it heats up quickly, but water does come out of the gimbal housing and exhaust prop -

when we hook up a hose to the top water pipe (see pic) it runs fine, no overheating-

any ideas? i have a 351 searay but not familiar with the odd plumbing happening at the back on the exhaust elbow.. theres a bolted on plate with 3/4" pipe going in and another out -


Also - i removed as much on the front with thick water hoses (2 brackets) but only saw square holes, nothing that could house a thermostat either
confused - pls shed some light thanks!
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Old 22-05-2017, 20:32   #2
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Re: mercruiser overheating - impeller good ??

opps - 4got pics

[IMG][/IMG]

the brackets removed from the front:

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Old 23-05-2017, 18:46   #3
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Re: mercruiser overheating - impeller good ??

Looking at the pics there appears to be lots of scale in the water passages. I forget the exact numbers but a very thin layer of scale causes X amount of temp increase.
I would consider a cleaning of water passages and then take it from there.
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Old 23-05-2017, 19:02   #4
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Re: mercruiser overheating - impeller good ??

In addition to the scale in the raw water cooling passage, it looks like there is also corrosion in the exhaust gas passage.

Remove the silver gasket material to examine for the amount of solid wall thickness between raw water passage and exhaust gasket passage.

If there is too much corrosion, then the exhaust parts must be discarded to prevent engine damage.

My boat is used in salt water and I redesigned the exhaust, from no raw water flush possible, with salt water sitting in the expensive cast iron 24/7/365, to now doing a fresh water, then soapy water, then Salt Away flush after each usage. Then I drain bone dry until the next usage.
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Old 24-05-2017, 07:29   #5
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Re: mercruiser overheating - impeller good ??

I recall an over heating problem on a similar '67 Mercruiser. The impeller (accessed by splitting the drive unit) appeared to be ok until it was compared to a replacement. The replacement was much stiffer. Installed the replacement and the problem was resolved.
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Old 24-05-2017, 07:51   #6
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Re: mercruiser overheating - impeller good ??

I have also had a perfect looking impeller not work, in my case the bronze internal sleeve was actually slipping in the rubber, think spun prop hub
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Old 24-05-2017, 13:46   #7
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Re: mercruiser overheating - impeller good ??

Quote:
Originally Posted by a64pilot View Post
I have also had a perfect looking impeller not work, in my case the bronze internal sleeve was actually slipping in the rubber, think spun prop hub

Had this happen on an old evinrude. Change the impeller to be sure. Could disconnect hose that connects to engine that runs the raw water while it's on muffs and running for a few seconds to see if there is flow.

I think just looking at the pics it's time for new exhaust manifold and risers. Probable a new thermostat housing too.
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Old 24-05-2017, 14:30   #8
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Re: mercruiser overheating - impeller good ??

All the above is good advise. start wit the impeller, it's the cheapest fix. But that manifold looks like it's ready to go. You can take it to a radiator shop to acid bath, inspect and pressure check, but since its a 4 banger and only one manifold, I'd replace. Aftermarket from Barr, Osco, or others are not that much. They are all over the internet. If it lets go, your engine is gone.
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Old 24-05-2017, 14:35   #9
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Re: mercruiser overheating - impeller good ??

found a crack in the wate rpump tube running up by the ujoint bellows, so I guess problem solved, that explains why the water appeared to be going up somewhere and coming back out of gimble ring -

nesxt steps is to unfreeze the outdrive, its completely seized on. Tore boots off and sprayed penetrating oil a few times -

hold thumbs
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Old 24-05-2017, 14:56   #10
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Re: mercruiser overheating - impeller good ??

What part of the drive is stuck? Is it the two big bolts on the gimbal ring?
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Old 24-05-2017, 15:03   #11
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Re: mercruiser overheating - impeller good ??

whole darn thing - wont budge a hair, the bottom has come loose -i can move the gasket but top section, zero.

I think the splines have seized inside the motor.. u joints are loose.. its busy soaking, might even have to poke a hand propane torch up there (last resort). i think the bearing has a teflon seal thats stopping the penetrating oil from getting in there..
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Old 24-05-2017, 15:05   #12
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Re: mercruiser overheating - impeller good ??

fyi ive never had one seize despite this being my 3rd drive im working on - theyre pretty straight forward..

even bust a hydraulic hose trying to push it out with the tilt pump and a block of wood :|
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Old 25-05-2017, 04:27   #13
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Re: mercruiser overheating - impeller good ??

Hmmm. Yeah soak and give it time. Might be worth turning the engine over with that oil up there. Might bust loose some of that.
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Old 25-05-2017, 09:41   #14
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Re: mercruiser overheating - impeller good ??

I had one of those old 60's Model One drives back in the 80's. I believe you can still find parts for them if ya got old marine engine shops where you live.
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Old 25-05-2017, 09:48   #15
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Re: mercruiser overheating - impeller good ??

I have to concur with several posts above. It looks like you are ready for new manifolds and risers. if you are boating in saltwater, you are looking at replacing these about every 5 years.
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