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Old OMC overheating 1971 307

R

RumGuy

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I have a problem that I believe I have narrowed down to the 1971 Stringer outdrive: The engine is a GM 307.
I have good FLOW through to my intermediate housing, but no PRESSURE. When at any planing speed, my engine temp climbs, and water flow goes primarily to the left manifold. Removing the inlet hoses and blocking them shows that the flow is EASILY stopped- no spray at all. The manifolds, engine water pump and T-stat are all new. I am planning on removing and inspecting the outdrive, but would love to know what I am looking for.
 
Re: Old OMC overheating

Sounds like the Impeller in the Stern Leg is suspect.

You should have a good stream of water coming out of the "Tell-tale" hole at the bottom of the Starboard Pivot Point where the Leg hinges up and down.

Are you running the Thermocon Develvo Cooling system?

Bruce.
 
Re: Old OMC overheating

No need to remove the entire drive.

Have a table or a large cooler or chair ready on the starboard side.

On a trailer lower the bow as far as it will go, and raise the drive 1/2 the way up.

Remove the very top bolts, and the exhaust and the lower will come down. place it on the table and tie it to the swim platform. be careful of the cable don't pull on it plenty of play in the cable.

remove the 4 bolts facing u in the upper drive from the bottom and the whole waterpump and shaft will come out. you could raise the drive a little more to make it easy, i sit on a milk crate when i pull the pump.
 
Re: Old OMC overheating

I do not know what cooling system it is-raw water from the lake, new log manifolds, and at this point, some cussing and blood.

Unfortunately I don't have a trailer: The boat resides in a boathouse. Pulling the drive is not a big issue, aside from the glad hand shift wire connection behind the transom cover. Pulling it off reduces the chance of any oil in the Lake.
I have had the drive impeller out and actually replaced it not long ago HOWEVER because my exhaust does not go through the drive, I did not pay close attention to the gaskets that I THOUGHT pertained just to that. New gaskets and permatex this time. This may seem a foolish question, but does the impeller rotate WITH or AGAINST the rotation of the shaft? Is it paddling the water or cupping it?

Thanks
 
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Re: Old OMC overheating

not quite sure what you are asking, but with the drive on the bench, if you face the ball gear of the upper, turning it clockwise is the way it turns when the engine is running.
I always have to give it a turn or two to remember which way to orient the vanes.
 
Re: Old OMC overheating

That's the question: Do the vanes curve with the flow or should I set them curving away , creating a cupping of the water? In other words, if we compare the housing to a clock, should my 12 o'clock vane curve toward 11 or 1? As it is now, with the CW rotation, I am pointed toward 11.

I appreciate the help that you are offering.
 
Re: Old OMC overheating

ok say the pump housing is flat on the bench the tips point right. The impeller turns left counter clock wise. I made a diagram when i removed mine the first time in the manual i knew if i didn't i was gonna get f--ked .
 
Re: Old OMC overheating

Well, that's both good and bad news: Good because that is how it is now, bad because my flow is poor. It comes apart this Friday. BTW- If you want a nice day on the Lake in NH, this Friday will be the best of the year---because I will be stuck on shore!
 
Re: Old OMC overheating

Did you remove the hose coming in from the transom that goes to the t-stat housing, or heat exchanger, and hold it up and have water going to the drive start the boat and see how high the water goes?

I didn't see you reply to the question if you got the"tattle tale" stream ether.

You have to determine if you got good water coming into the motor. If good water coming into the motor then you have to determine if the engine mounted water pump is good.

Then you have to determine if your equipped with a power steering cooler or any other heat exchanger is clogged.

One other thing maybe the most important, have you checked the t-stat ? Half frozen closed maybe ? But thats the first thing to check some change them every year.

Some don't use one but thats for another thread.

Then you have to determine if the risers are clogged or the flapper if equipped is blocking the exhaust.
 
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Re: Old OMC overheating

Well....everything that I do makes things BETTER, but not great: Removed and sealed the drive water pump, and now have some pressure coming up. The tattle tale streams are stronger. Reset the ignition timing, but found that the dist. cap is leaking voltage (found that out when turning it for timing-ouch) AND-more importantly that the intake manifold was changed a while back, and that is when temp issues arose. The replacement manifold and gasket were GM truck. Is there a water porting difference in manifold OR gasket between the GM truck manifold and a marine manifold that may be the culprit? I have ordered new intake manifold gaskets that APPEAR to have larger cutout areas as an option. I appreciate the help that you all have offered.
 
Re: Old OMC overheating

have you greased the swivel bearing really well to eliminate exhaust gas getting sucked in the water pump inlet?
there's also a seal in the bottom of the exhaust housing that needs to be in good shape to keep that grease there.
 
Re: Old OMC overheating

I did grease it well, but to keep the seal on the water side tight. This vintage boat could not exhaust through the outdrive in the 235 HP model, therefore I have through hull exhaust. When I start up in a public place, heads turn , but all in the wrong direction; no one expects my old tank to sound as cool as it does!
 
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