1965 gm 120 mercruiser overheating

[CamaroMan]

Hi there, got a buddies gm120 going today, rebuilt the carb and it was idling instantly with a cold engine - very happy. after 2 mins on the muffs the temps were really high and we cut it.

I noticed water was running from the gimble housing which i think indicates the impeller is working (dont worry we are putting in a brand new kit next week). So i took off the water hoses and brackets on the front of the engine, no thermostat, the cast holes were all square, i couldnt see any where a t-stat could go? Did these motors even come with them?

Also - the block was dry, shd i fill the block with water to prime the circulating pump? is it possible starting it dry would not circulate water? There was some water sputtering out the prop -

so ima bit confused, all signs say water is moving but block is dry ? Could the impeller pump be pushing water up and back down without going thru the block?

Also do/did these things have exhaust flappers?

The bellows all look good, flexible and i pulled and inspected closely, not even a sign of a crack or perishing -

thanks!

 

[Bt Doctur]

http://www.boatfix.com/merc/Servmanl/13/13A6R2.PDF

 

[CamaroMan]

No Title

http://www.boatfix.com/merc/Servmanl/13/13A6R2.PDF

Hi - that manual is for the 3.0, but I believe we have the 2.5 / 153 mercruiser, the front looks different to whats on my buddies boat -

cant see any place for a stat in there, all square holes.

Well yesterday we got her running by putting a hose on the top line (see pic) and she ran fine, however when running on muffs the water is not getting pushed up. We did take the impeller out and it was in excellent condition, had it out and were at west marine and after2 ppl told us it looked good we put it back in, was still soft and no cracks.. wear plate was brand new as well -

 

[CamaroMan]

is it possible the water is going up to exhaust and straight back down thru exhaust? there is water flowing from the gimbal housing when it runs on the muffs indicating the impeller is pushing water somewhere..

There is a 6 or 8 bolt plate on the exhaust elbow with 2 hoses about 3/4" thick going int, like theres some kind of a system.. ill take a pic today and post it - but no clue whats happening there..

thanks

 

[Bt Doctur]

back up a bit too, need a wider look. Cant find that housing nowhere, not even in manual 1

 

[Bondo]

Ayuh,.... Somebody at some point has re-engineered that coolin' system, in what appears to be a very Bad way,....

That's not at All how it's Supposed to be,....

 

[CamaroMan]

No Title

well im starting to think something at the back is faulty too.. when we hose it - perfect.. the hose coming from the bottom from the impeller comes to the back of the manifold - theres a plate with about 8 bolts, another tube goes to exhaust down elbow - its as if the water is going up and straight back down there and not making it into the engine.

Ill have to take it apart and see where water IS coming in and go from there.

How does the water system work in this manifold? I presume the water comes up from impeller/pump - into circulating pump, and from there thru block and back to the exhaust? shd i be looking for 2 separate passages in the manifold?

simple drawing shows what there is at the back - its as if the water is going from a to b, then straight to C and then to D (back down)..

Sorry i dont have a pic, the darn camera didnt shoot when i pressed the btn and it was very sunny. Its socal here so i can understand why the stat is maybe missing, but not the whole housing -

 

[Bt Doctur]

That setup has never been seen, thats why we need pictures of it. The typical setup is what is shown in the link I posted.

 

[CamaroMan]

so started tearing bellows apart since the outdrive is stuck to spray in some penetrating oil and saw a slice in the water hose going from pump to engine, so I guess problem solved, we one of them - now to unseat the spline/shaft from whatever its stuck on - bearing or engine?

thanks all for the help, new bellows kit is on the way with all new bits. Guess a ujoint bearing set is also in order there -

 

[Bondo]

saw a slice in the water hose going from pump to engine, so I guess problem solved,

Ayuh,..... The entire coolin' system you've been describing is Pooched,... it's All Wrong,....

It'll never be Dependable in the poor condition it's in,....
Backyard engineerin' at it's worst,...

 

[CamaroMan]

well its just age - it stood for quite some time - perishing hose has little to do with backyard engineering, its wear and tear. hopefully it will be sorted once we get the outdrive off, been spraying penetrating oil in there all day.. will head back 2moro with a propane torch and prybar and see if we can make some progress.

 

[Grub54891]

I'm subscribing just to see what happens with the torch.

 

[Bt Doctur]

You never want to pry on a drive to remove it. You can place a piece of wood between the top of the drive and the transom and use the hyd rams to work it off by increasing the wood length.
pictures, pictures, pictures

 

[CamaroMan]

No Title

got it off, fyi bust a hydraulic hose trying that "trick". The entire upper ring assembley was so corroded - nothing badly damaged and finally got it off (without torch!).

Have new ujoint bearings, bellows are on the boat side - the shift cable we received however screws in from the back and ours came out from the front.. do we tap the threads thru or what? any idea on the tap size?

 

[Alumarine]

Here's a link to a service bulletin.
As the instructions say, only use a straight tap. They are not easy to find locally but are available online.
A machine tool and die supplier might have them.

 

[Bt Doctur]

pics and links in your other post

 

[Alumarine]

Oops, I forgot the link but I see the doctor got you covered in the other post.
www.boatfix.com/merc/bullet/83/83_27.pdf