2.5 OMC cooling system

[Shadow91]

Okay, so im trying to understand how exactly my cooling system works in my '83 OMC 2.5l engine. I recently replaced the raw water pump and have checked to see if im getting flow or not with the engine running. If i remove the upper hose on the left (refer to picture) I have a nice stream of water coming from it. However I dont have anything but steam coming from the hose on the right.

I also noticed i had a pretty good leak coming from what appeared to be the bell housing area. Not sure 100% as i didnt want to keep running the engine, but i had noticable water pouring out from where the bell housing mates up with the engine.

Any and all help is greatly appreciated.

 

[Scott Danforth]

the upper hose on the left is the line from the outdrive to the thermostat housing that supply water to the motor. the big hose on the left is the circulating pump hose

the small hose on the upper right you have disconnected is the water exit from the block that feeds the water cooled exhaust manifold. from there the water goes out the water cooled exhaust elbow and mixes at the rubber exhaust hose with the exhaust gasses.

if you have no water shooting out of the thermostat housing with the water hose disconnected like that, and you have water entering the motor, you have a big leak somewhere filling your bilge. you should have as much water exiting the thermostat housing as there is coming in from the raw water supply hose.

 

[Shadow91]

Okay, so I would assume my leak from the back of the engine is probably my root concern then. From lots of google searches id say more then likely I have either (hopefully) a rotted/pushed out freeze plug or a cracked block.

Am I able to pull the engine with the drive still attached to the boat or am I looking at removing the drive in order to remove the engine? Any suggestions to confirm the freeze plug in the back is the cause of the leak?

Ive been running it using a hose and muffs, and definitely have a major leak from the rear of the engine that gets worse the higher the rpms, filling the bilge. Dont know what else is back there that would leak.

 

[Bondo]

Am I able to pull the engine with the drive still attached to the boat or am I looking at removing the drive in order to remove the engine? Any suggestions to confirm the freeze plug in the back is the cause of the leak?

Ive been running it using a hose and muffs, and definitely have a major leak from the rear of the engine that gets worse the higher the rpms, filling the bilge. Dont know what else is back there that would leak.

Ayuh,.... There's a big core plug back there, no doubt yer problem, probably from freezin' it,....
Hopefully, it pushed out, before the block cracked,...

Yes, ya gotta pull the drive 1st, then the motor,...
Goin' back together, ya drop in the motor, align it to the gimbel bearin', then slap the drive back on,....

 

[Scott Danforth]

Shadow91, I would quit running the motor as you will toast it without cooling water. if you toasted your motor or you have a crack in the block from improper winterization, look for a 3.0 to replace it with.

Bondo, this is an OMC stringer based on the above pic. pull the drive is remove the shift cable, undo the trunion caps and pick up the drive and set it in the corner. then undo the big boot, then undo the 4 motor mounts and lift the engine and intermediate housing together as a unit.

no transom shield or alignment

 

[Shadow91]

Scott, I havent ran the engine but for maybe 5 minutes yesterday while checking it all out after replacing the raw water pump. After i noticed the leak in the back and no water flow out of the thermostat housing I shut her off. So hopefully no more engine damage has been done.

And if the block is cracked, why do you recommend the 3.0? Other then the obvious HP increase, any other reasons?

And you make it seem very easy to get to the engine. Ill start ripping into it tonight and hope for the best. Really appreciate all the help youve given me. Its been quite the learning experience.

 

[Scott Danforth]

because the 2.5 liter is not a stellar performer and the 3.0 will drop in its place (and is more plentiful)

When I pulled my motor in the avanti, I had never done it before, and it only took me about an hour to have the motor hanging from the cherry picker over the back of the transom.

however I have had the drive off many times

be careful pulling the drive, you dont want to damage the lower shift cable. its over $500

 

[Shadow91]

Well I have it basically ready to come out. Just need to pick up an engine hoist tomorrow and out she comes.

Other then the damn screw for the steering. I can't get that sumbitch to turn to save my life!

 

[Shadow91]

Okay, got the engine out tonight, which let me say. was FAR easier then i had hyped myself up for. Removed the intermediate housing and as i was taking it off, out fell the freeze plug. Ive looked all over engine looking for signs of rust trails or cracks and as of right now do not see any. So HOPEFULLY ill be golden after i install a new plug.

Now then, ive read to use only brass plugs? Just take the old steel one to an auto parts store and match it up with a brass plug? Neighbor said to use an expanding rubber one, but i feel like that would rot after a few years..

And while looking inside the engine through the freeze plug hole I noticed quite a bot of rust flakes internally.. Is that normal? Or am i looking at more issues down the road? Or just clean up the best i can and dont worry about it?

After pulling the engine.

The engine on the jack

The back of the engine

the plug itself, which looks completely okay.. Kinda worried about what made it come out..

The heavy rust flakes inside the engine that im concerned about..

And then what the heck is this hose? I see some wires going to it, but its just been flopping around the back. No idea what it actually is or what it does.

And other then just doing a heavy cleaning of the bilge and boat itself, what else do you recommend doing while the engine is out? Oil pan looks clean and dry, and i dont have any oil leaks i see other then some light seeping from the valve cover. Just want to do as much as i can while im this far apart.

And back on the subject of the freeze plug, how exactly is the best way to install one? Just tap one in with a hammer or do i add some sort of sealant to it as well?

Thanks for all the help!!

 

[kenny nunez]

Use #2 black Permatex , Try to back flush the engine to get some of the scale and what ever else comes out of the rear freeze plug hole. It would have been a lot easier to un bolt the engine from the adapter housing rather than removing the whole unit. I was an OMC dealer from 72- 03.

 

[Shadow91]

You are you saying use the #2 on the freeze plugs i assume?

And i removed the entire unit for a couple of reasons. It was very simple this way, doing this gave me a better understanding of how the whole system works and allowed me to check condition of the whole power train. Im a very visual person so by putting my hands on it and physically seeing how it all goes together allows me to understand its function best.

Just ordered new gaskets for the intake, exhaust, new exhaust hoses and a new thermostat as well as the hose that blew out. Hopefully then I can get this thing to be reliable on the water!!

 

[kenny nunez]

That is the stuff that always worked the best for me. I know you will throughly clean the hole in the block before installing the plug. You also may want to run the engine before it goes back in the boat in case there are some other problems.

 

[Shadow91]

Whats the best way to run it out of the boat?
Flywheel on, hose hooked up to the raw water hose that would be coming from the intermediate housing? What about exhaust? And then when it is running (correctly) I would assume I should see plenty of water coming out of the exhaust as well, correct?

Or hook up the intermediate housing first?

And obviously just attached to 12v battery..

Anything else?

 

[ab59]

I think that you should replace ALL for your freeze plugs if they are not Brass. Now's the time to do er since it will never be easier than while you have the engine out , but I dunno .

 

[Shadow91]

Well finally got everything for the boat today. Got all new freeze plugs, engine repainted, thermostat and most new gaskets!

Now with that boot on the transom, should I use any kind of sealer on it, or just screw it all back together and I'm good. There was none on it when removed. And what kind of sealer if I should?

 

[Shadow91]

Oh! Anyone here know if a bad thermostat could have been the reason for the rear plug getting pushed out? The old plug was brass and looks like it had been replaced before. But when I started pulling the thermostat housing apart to replace it it was gone! Found all the pieces at the water pump outlet. Wondering if by some chance it would be possible to block a passage it it created too much pressure, pushing the back plug out? Has anyone seen anything like that, or just wishful thinking?

 

[Bondo]

or just wishful thinking?

Ayuh,.... Only Ice can build the pressure necessary to push out a core plug,....

 

[Shadow91]

I figured. Like I said I was mainly just hopeful. Still haven't found any signs of a cracked block however. And oil is nice and clean.

Speaking of oil, what you all recommend to run in it? Do boats take a speciality marine oil, or is it just typical automotive 10w30 or the likes?

Gonna look up what factory uses, just curious if there is something people like better vs what they used 30 years ago

 

[Shadow91]

Getting ready to put the engine back in. Was told to put marine Tex into the bolt holes for the motor mounts. Is that the proper way to seal the wood or any other methods besides marine Tex?

And for sealing the transom boot, just marine silicone or what? I've read a bunch of different options for it and my local marine store told me to use like 5200 or 5400 (can't remember exactly)