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OMC 250 (chevy 350) cooling System

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jdmack0208 View Drop Down
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    Posted: August-09-2009 at 1:31am
Does anyone have a diagram or can you post pictures on the entire cooling system set up for an OMC 250(Chevy 350)Reverse rotation motor. I need to verify that I have the manifolds and the rest of the cooling system plumbed correctly. I will include a picture of mine and hopefully someone can post theirs and I can compare.

I overheated pretty bad today on the lake and I want to try to fix the problem.

Also the 2 grommets that are on the valve covers have 90 degree elbows on them, is this supposed to be the PCV valve and just a 90. You can see both of mine are blowing in to nothing.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote eric lavine Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:46am
yes, only 90's in the valve covers then up to the arrester,
where do those lines on the risers exit too?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:51am
OK let me see if I can explain this, the two hoses that are going in to the elbows on the risers is coming from the water pump. They are not connected that way now nor were they yesterday. Right now they go in to the top tubes on the thermostat housing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 10:23am
I took all 6 peices of the impeller out of the water pump housing, thats right 6. So since Bought this boat I have paid to have the impeller replaced and been told there was a new one in there by the PO.

So now what would cause me not to pump water if the impeller was good thus causing it to multiply in to six pieces. I am gonna replace the impeller and thermostat for sure, then shoot water up the inlet to check for obstructions. The only thing left will be to find out if the plumbing is actually correct with the type of manifolds and elbows that I have. A picture of a similar one would be great.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 11:05am
it would be interesting to know why does it need all those hoses?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 12:14pm


OK The hose's with the red lines and are no going to where they are pointing on the pic. The yellow line indicates the hoses that are now going to the risers. The red line hoses are coming directly from the out on the water pump housing.

I am going to take some pics of the water pump because I cannot figure out which impeller I need to order.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 1:07pm
Ok so I just took off the valve cover on the right side in the picture and found three loose valves. Anyone have a procedure for adjusting these? Pictures of the water pump are on the way.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 2:04pm
Here is the inside of the impeller housing.



Here is the outer view



Here is the way the last mechanic ran the plumbing.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 2:38pm
Ok here are some questions I need answered before I can continue.

1. Water comes in to the make up pump from the bottom of the boat then goes to the trans cooler then where. Right now it is going to the top of the motor via a T-connector.

2. On the risers, the two hoses coming out are anti-syphon valves, do I need these. I have seen nothing on here about them but on the Osco website it says the risers are equipped for anti-syphon valves and points to those two holes.

3. The water is supposed to go to the manifolds then on to the motor correct? The manifolds are supposed to heat the water up a bit before it hits the engine? If this is the case and I remove the hoses from the anti-syphon valves and get plugs for them then which hole on the manifolds does my raw water from the impeller go in to and where does the output of the manifolds go on the engine.

I am gonna lick this and get my boat back in the water next weekend.

Josh
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75 Tique Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 2:56pm
Originally posted by jdmack0208 jdmack0208 wrote:



I am going to take some pics of the water pump because I cannot figure out which impeller I need to order.



JD,

The impeller you want is

Sierra part no. 18-3086 or OMC part number 379475

Should be easy to find as it is the same impeller used in newer OMC outboards.

I had the same water pump (on my 76 305) until it finally bought the farm. Couldnt find a replacement and even Depco said they couldnt repair it...so you've got that to look forward to. I had to replace with a crank mount.

Despite having a similar engine, I can't help you with the cooling piping question as I have different manifolds. Just two hoses come off the t-stat housing into the front of the exhaust logs on mine.



Maybe we can hook up some time. I usually spend a couple weeks a year (except this year) in seven lakes, just the other side of Pinehurst.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 4:21pm
Well took the thermostat housing off and what do you know, there isn't one in there. This boat is killing me. I can't figure out the cooling thing. I have five hoses that go in to where the thermostat is supposed to be, that's 3 more than everyone else. I know that I am not supposed to be pumping water straight to the engine from the river but that seems to be what I am doing right now. No one has these odd ball manifolds and risers from osco.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 6:07pm
The bracket deal on the top of the arrestor, can you buy just that piece or do you have to buy a whole new arrestor. Mine does not have it and the hoses coming out of the valve covers were just laying on the engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote almabes Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 8:41pm
After looking at your pictures, and scouring the 'net for any kind of diagram I have come to the conclusion it looks like mechanic #2 has hooked up your cooling plumbing correctly.

From what I found on various internet forums, it looks like your manifolds are set up to allow for a fresh water cooling system to be optionally installed.

From what I can tell from the last picture of your plumbing the water does the follwing:

1. gets sucked through the pickup on the bottom of the boat.
2. goes through the trans cooler
3. goes into the RWP. RWP output goes back under the engine.
4. hose from RWP output goes to a T-fitting and connects to the top/front of the thermostat housing
5. Water flows into the block through the circulation pump. Once the block fills excess water will flow out of the t'stat housing through the back pair of hoses into the "bottom" of the exhaust manifolds.
6. water comes out of the exhaust manifolds at the top of the pyramid
7. water is injected into the exhaust stream through the anti syphon valves in the risers.

I found a plumbing diagram, that looks somewhat kinda sorta close to what you have. It's for a freshwater cooled setup. You'll just have to mentally block out the heat exchanger...
Sorry I can't be any more help. The one thing that's pretty straightforward on my PCM Ford is the cooling system plumbing.


The diagram...confuse yourself at your own risk!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote almabes Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 8:47pm
The only thing I don't like about how Mechanic #2 hooked the plumbing up is the bends in the hose between the bottom of the pyramids and the anti-syphon valve in the riser. It looks like the hose is bent so much it collapses. Just to be safe you may want to look at installing a longer loop of wire reinforced hose there, or hook up the left pyramid to the right riser and vise-versa.

I may be totally off base here. If I am, just ignore me.

Thanks,
Anthony
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 8:56pm
how long did you ran the boat before it overheated?

It seems the plumbing is OK... just a bad impeller after so many cranks without water.

If not you can feed the thing with water, turn it on and try checking out each hose at a time so you can follow the water stream.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 8:58pm
Do I even need the anti-siphon valve connection or can I just eliminate it all together, no-one else seems to have this. My thinking is that I should run the water from the impeller to the bottom fittings on the thermostat housing. The top fittings will go to the manifolds. and the anti-siphon be gone all together.

Another thought is this, water from the impeller goes in to the top connections on the manifolds and the end connection on the manifolds go to the bottom fittings on the thermostat housing(this will make sure the water is warmed up before going in to the block(I read that in my 1976 correct craft owners manual). Then run the top connections of the thermostat housing to the anti-syphon valves on the top of the risers thus eliminating the water that isn't needed out the exhaust.

I think I can test all these theories tomorrow if I put the water hose on the outlet of the impeller and see which way gets water to my engine.   I should be able to pick up a thermostat and gasket tomorrow. If that all works then when the impeller comes in the mail I can test it on the hose that way. Last test may involve my kids pool and an air tight connection to see if I can suck water out of the pool.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote almabes Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 8:58pm
Luciano,
Did my description seem correct?

Thx,
Anthony
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:00pm
I never ran it without water, it would never start when I got it back from mech No. 1. Mech no. 2 said he had it running on the hose. I don't know. I am gonna do just what you said, try different ways to get it to work. Biggest thing is fixing all the stuff I found today ie thermostat and getting the temp gauge to work.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote almabes Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:04pm
How about this:

Water from RWP to bottom of pyramid
Water from top of pyramid to top of t'stat housing
Water from back/bottom of T'stat housing to anti-syphon valves.

Incoming water needs to go to the front/top. Otherwise it will be dumping on top of the thermostat, which when open will have the RWP battling with the circulation pump.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:07pm
yes it makes sense... but I'd turn it on and check each hose, it's simple, one sucks water and the other spits it.

I dont see why you want to open the T. housing.

This system seems pretty unnecesary complicated, if you could find out this parts arent any specific for this engine, thus needing the complicated hose arrangement I'd consider making a simpler install avoiding so many hoses/connections.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:13pm
I opened it thinking maybe I had a bad T-Stat, turns out there wasn't one in there. I would like to eliminate some of the hoses too but what I cannot figure out is why I have 4 hose inlets going to the top of the t-stat housing.

Aren't the manifolds supposed to warm the water going in to the t-stat housing.

Isn't the top connections on the t-stat housing basically an overflow that can be routed out the anti-syphon valve.

Shouldn't the anti-syphon portion keep positive suction on the top portion of the t-stat housing?

Tomorrow after work I will try to follow the water path and hook it all up. Once I get the t-stat in the boat will start right up as long as I am feeding it hose water.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:22pm
I dont know why you want warm water fed into the engine... I think most if not all engines running I have seen have water feed from the water pump directly into the engine and then into the exhausts.

You possibly have to inlets on the T housing and 2 outlets when a normal engine has only one inlet and 2 outlets (1 for each manifold)

If the thing was not plumbed correctly and you cranked it, it might have ran without water... you also dont know what mechanic number 2 tried with it to make it work.

SO first off start the new impeller, and then start pulling hoses.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote almabes Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:31pm
Honestly, call Discount Inboard Marine on Monday. They will probably be able to give you a better answer about your cooling system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:31pm
So water from the impeller to the t-stat housing, t-stat housing to bottom connections on the manifolds then leave the anti-syphon portion the way it is or eliminate it all together?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:34pm
Once I get the t-stat in tomorrow I am gonna be ready to test. I should have no problems if I hook the garden hose up to the outlet hose of the impeller housing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote almabes Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:35pm
I vote leave it.
On third thought, those connections at the top of the riser are to provide a one-way valved drain for water in the risers that could make its way into the dry side of the exhaust manifold.
This is a strange setup.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:36pm
I don't think hooking the water supply up to the top connections is the best idea as there are only two little holes in there to allow water through.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:39pm
First try it as is... the important thing here is to have good flow inside the engine for cooling.

Then you can try taking it away and see if it still works.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jdmack0208 Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:45pm
The mechanic did say he ran it for a while on the hose while they were tuning it. With it on the hose the impeller wouldn't have mattered cause there was constant pressure. He said it was cooling fine. I will leave it the way he had it only with a 160 degree t-stat installed and run it on the hose for a while at idle. If the t-stat opens up and the motor cools then it should be good to go once I get the impeller in the mail. I really do appreciate all the help you guys are giving me. I spent a lot of money at the mechanic and really the only way this boat is gonna run now is with me fixing it with the help of guys like you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luchog Quote  Post ReplyReply Direct Link To This Post Posted: August-09-2009 at 9:57pm
He said the boat cooled correctly and you got a boat with a trashed impeller...

The thing is an engine can be run without any water (or an improperly plumbed system) for several minutes and it wont get hot, so the only way to test it's cooling properly is by pulling the hoses.
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