OMC 250 (chevy 350) cooling System
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=14840
Printed Date: April-25-2024 at 5:39pm
Topic: OMC 250 (chevy 350) cooling System
Posted By: jdmack0208
Subject: OMC 250 (chevy 350) cooling System
Date Posted: August-09-2009 at 3:31am
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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.  ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Replies:
Posted By: eric lavine
Date Posted: August-09-2009 at 11:46am
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yes, only 90's in the valve covers then up to the arrester,
where do those lines on the risers exit too? ------------- "the things you own will start to own you" |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:51am
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-09-2009 at 12:23pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: Luchog
Date Posted: August-09-2009 at 1:05pm
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it would be interesting to know why does it need all those hoses? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 2:14pm
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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-09-2009 at 3:07pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-09-2009 at 4:04pm
Here is the inside of the impeller housing.
Here is the outer view 
Here is the way the last mechanic ran the plumbing. 
------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-09-2009 at 4:38pm
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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 ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: 75 Tique
Date Posted: August-09-2009 at 4:56pm
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. ------------- _____________ “So, how was your weekend?” “Well, let me see…sun burn, stiff neck, screwed up back, assorted aches and pains….yup, my weekend was great, thanks for asking.” |
jdmack0208 wrote:Posted By: jdmack0208
Date Posted: August-09-2009 at 6:21pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-09-2009 at 8:07pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: almabes
Date Posted: August-09-2009 at 10:41pm
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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. http://www.baylinerownersclub.org/forum/showthread.php?t=28264 - The diagram...confuse yourself at your own risk! ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: almabes
Date Posted: August-09-2009 at 10:47pm
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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 ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: Luchog
Date Posted: August-09-2009 at 10:56pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 10:58pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: almabes
Date Posted: August-09-2009 at 10:58pm
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Luciano,
Did my description seem correct? Thx, Anthony ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:00pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: almabes
Date Posted: August-09-2009 at 11:04pm
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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. ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: Luchog
Date Posted: August-09-2009 at 11:07pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:13pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: Luchog
Date Posted: August-09-2009 at 11:22pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: almabes
Date Posted: August-09-2009 at 11:31pm
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Honestly, call Discount Inboard Marine on Monday. They will probably be able to give you a better answer about your cooling system.
------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:31pm
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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? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:34pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: almabes
Date Posted: August-09-2009 at 11:35pm
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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. ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:36pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: Luchog
Date Posted: August-09-2009 at 11:39pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: jdmack0208
Date Posted: August-09-2009 at 11:45pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: Luchog
Date Posted: August-09-2009 at 11:57pm
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: almabes
Date Posted: August-10-2009 at 12:18am
Unless I am mistaken, raw water cooled GMs run a 145 degree thermostat. with a 160 the motor will get too hot. ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: almabes
Date Posted: August-10-2009 at 12:39am
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From what I see at various purveyors of OMC parts, I am, indeed mistaken. 160 degrees is the appropriate temperature thermostat. ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-10-2009 at 12:41am
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Cool, thanks....I will let you guys know what I come up with tomorrow. I will take the laptop out there with me and update this thread. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: almabes
Date Posted: August-10-2009 at 12:42am
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Oh no...I'm working from home tomorrow...I guess that means I'm really checking this thread tomorrow.
Good luck. I've learned more about OMC inboards than I've ever thought I would. ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-10-2009 at 12:44am
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Well on a positive not, the boat ran strong until it overheated. No more bogging out. It never planed out though, what would be the reason for that? Speed? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-10-2009 at 12:49am
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Don't worry though I have plenty of other stuff to fix(tach, speedo, depth gauge etc...)so plenty more threads coming and you'll learn a lot more! ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: eric lavine
Date Posted: August-10-2009 at 10:13am
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im taking my camera today and will snap a pic of a similar omc, it should give a general idea of hose routing ------------- "the things you own will start to own you" |
Posted By: almabes
Date Posted: August-10-2009 at 4:01pm
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OMC:
Obviously More Complicated? ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: boat dr
Date Posted: August-10-2009 at 6:03pm
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OMC
Other Motor Company ------------- boat dr /diaries/details.asp?ID=4631 - 1949 Dart /diaries/details.asp?ID=1533 - 1964 American Skier |
Posted By: almabes
Date Posted: August-10-2009 at 10:08pm
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OMC:
Only More Confusion! ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: almabes
Date Posted: August-11-2009 at 4:51pm
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Josh,
Any luck running her on the hose? ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-11-2009 at 11:22pm
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I have all the thermostat and gasket but I got off work late last night and today it is raining so maybe I will get them in tomorrow. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: eric lavine
Date Posted: August-12-2009 at 10:24am
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I looked and it doesnt have half of the hoses you have. i dont think it will help ------------- "the things you own will start to own you" |
Posted By: almabes
Date Posted: August-12-2009 at 12:13pm
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I have sent an e-mail to a marine mechanic friend of mine, and asked him to take a look at the pictures.
Hopefully he can help figure out the plumbing. ------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |
Posted By: jdmack0208
Date Posted: August-14-2009 at 12:45am
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Ok here is the link to the manifolds I have, the file is a PDF and I don't know how to post it.
http://barrmarine.net/wordpress/omc-v8-4/ And here is the link to the risers: http://www.oscomotors.com/catalog/catalog31.asp It doesn't say anything about closed cooling system. I don't know, it won't stop raining here for me to get out there and hook everything up. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: jdmack0208
Date Posted: August-14-2009 at 12:47am
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This is what I got from the guy that the guy I bought the boat from got it from(say that three times fast!) Not much help but at least he cares enough to email me back.
"Hey I believe there were 2 holes on the front of the old manifolds and the hoses went to the thermostat. I assume a newer style is being used now as the old one is no longer being made. You will probably have to get a different thermostat housing. Go to correct craft fan site and ask for a picture or to the manufaxcturer of the new system and ask for a thermo. matching the one you are using." ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: boat dr
Date Posted: August-14-2009 at 2:43am
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CorrectCraftParts has a set of used OMC late style manifolds for sale. Call Karen for prices and shipping. These are not after market fit all manifolds, but the real deal. 1-318-299-8547 ------------- boat dr /diaries/details.asp?ID=4631 - 1949 Dart /diaries/details.asp?ID=1533 - 1964 American Skier |
Posted By: jdmack0208
Date Posted: August-15-2009 at 4:19pm
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Ok so the boat is running on the hose, did not heat up and I left it running at idol for 20 minutes. Water is coming out of the exhaust as it should. The manifolds fluctuated from warm to cool, I don't know if that is normal or not. I am gonna have to buy a new t-stat housing because I couldn't seem to get the crack completely sealed. Gonna throw some more permatex on it and see if I can get is controlled. Of course the JB weld didn't hold once I tightened down the bolts. Researching the t-stat housing now. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=4682 - 76 Southwind BR |
Posted By: Luchog
Date Posted: August-15-2009 at 9:59pm
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I'm glad you figured it out!!
Now, I think you can do well with any chevy 350 housing, just that you might have to cover all those holes on your manifolds! by the way, how did you do it? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: almabes
Date Posted: August-16-2009 at 9:39pm
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Between Josh, myself and marine mechanic friend of mine we determined that four of those holes were extra, and basiclly adding confusion instead of helping cool the engine. They're probably there to accomodate a closed cooling system. Josh plugged all the extra holes in the manifolds with 3/4" NPT pipe plugs. It's more like the raw water colled PCM center rise pyramid setup now.
------------- favorite computer wisdom: net helpmsg 4006 '76 Martinique PCM 351W |