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  1. #1
    Join Date
    Aug 2009
    Location
    Oregon
    Boat
    Sea Ray
    Details
    1979 260 Sundancer Towed with 1999 F-350 4X4
    Engine(s)
    5.7 OMC 800
    Posts
    24

    350 OMC over heating

    Here is another over heating issue. The boat in question is a 1979 Sea Ray 260 Sundancer with a GM 5.7 OMC 800 drive.

    I have been reading lots of threads on over heating and have plenty of possible causes to investigate. But I still have some un answered questions.

    Here is a quick run down. I have only had her out 4 times in the past 2 years. That was because of both the upper and lower gear clusters failing while out on the water. They sure do make a lot of noise when they go bad. During repairs of the OD it was verified that the impeller was intact and in good shape. The shop who did the repairs says everything else in the OD is good working order.

    I just read a post about a Y tube and flapper in the out drive. Is this in the OMC 800 and could it be causeing me problems?

    I think the factory cooling system on this boat is raw water cooling. It now has a fesh water system that looks like it was shoe horned in between the front of the motor and fuel tank. So as not to assume could some one attempt to veryify from the attached photo if it is plumbed correctly. It looks ok to me but I am new at boating an marine mechanics.

    Last year I had pulled the water line from the OD to the heat exchanger and ran the moter. The flow seemed adequate. But how do I know what is adequate? I pulled the exhaust risers, they seemed to be ok. dirty and scalely in side, I scraped them. I haven't pulled the manifolds yet. Maybe that is next. Also I want to check flow from the heat exchanger to the OD to check flow there. How do I check flow of the out water through the OD? And speaking of heat exchanger, how do I verify it is sized properly? It seems a lot smaller than an auto radiator.

    I finaly got the OD on today after is was repaired 4 times since I bought the boat 3 years ago. I fired her up in the drive way with water hooked up to the OD. The temp kept climbing through fast idle to 240. I stopped the motor, let it cool, and replaced the thermostat. The old one was stuck open. (failure I guess) The same overheating occured when I started her up.

    Any suggestion would be greatly appreciated.

    Rob

    PS When I did have her out 2 years ago at full throttle I had trouble getting her up on plane and I could not get past 3400 RPM. Exhaust/water restriction issue?
    Attached Images Attached Images
    1979 Sea Ray Cuddy 260 Sundancer 5.7 OMC. Towed with 1999 F-350 Superduty 4X4. Portland, Oregon

  2. #2
    Join Date
    Sep 2008
    Location
    Bodkin Creek, Chesapeake Bay Md.
    Boat
    SeaRay 340 SDA
    Details
    2004 340 SDA
    Engine(s)
    8.1 V-Drives
    Posts
    516

    Re: 350 OMC over heating

    How old are your exhaust manifolds.
    George
    George & C.J.
    "CJSTOO"
    2004 340 D.A. 8.1 V. Drives
    "All that is necessary for the triumph of evil, is for good men to do nothing"

  3. #3
    Join Date
    Aug 2008
    Location
    Phila
    Boat
    Formula
    Details
    2008 Formula 310 Sun Sport
    Engine(s)
    377 x 2 w/BIII
    Posts
    281

    Re: 350 OMC over heating

    "The flow seemed adequate. But how do I know what is adequate?"
    The flow should make you say WOW thats good, I wouldnt use adeguate when the system is working properly.
    There is also a water pickup tube between the lower and upper OD unit and these can get blockage reducing water flow.
    SummerWind
    (VOR = WaterHog)
    2008 Formula 310 SS
    MMSI: 33806153
    Bohemia River, MD

  4. #4
    Join Date
    Oct 2008
    Location
    tehachapi Ca
    Boat
    SeaRay
    Details
    268 sundancer, humminbird 797c fish finder / chart plotter /gps combo, lowrance lms 400 with np-60 f
    Engine(s)
    OMC Cobra 1.41 final drive ratio. 5.7 rebuilt to 300 hp 11/ 08. Hustler 15. x 15 prop. reman quadraj
    Posts
    260

    Re: 350 OMC over heating

    yea it's plumbed right. Mine is all brand new and runs about 180. Check temps throught the system with an IR gun. Manifolds run about 200 ish. temp sensor about 170. risers about 110. heat exchanger top 170, bottom 110. Coolant runs through tubes inside big pipe with plugs (heat exchanger) raw water runs over and around them. I don't know how much volume of water should run through the exchanger but on the muffs, idleing, it takes what ever my hose puts out. probably about 2.5 gpm
    1986 268
    5.7 OMC cobra rebuilt to 300 hp 11/08, closed cooling system through the manifolds, 15.5 x 15 Hustler aluminum prop, mando 100 amp alternator, 1.41:1 final drive ratio, pertronix 1581 electronic ignition conversion with easa modification, reman quadrajet, more to come.

  5. #5
    Join Date
    Aug 2009
    Location
    Oregon
    Boat
    Sea Ray
    Details
    1979 260 Sundancer Towed with 1999 F-350 4X4
    Engine(s)
    5.7 OMC 800
    Posts
    24

    Re: 350 OMC over heating

    George,
    I don't know how old the exhaust manifolds are. they could be OE, or could have been replaced with the block. What serial numbers I could get off the block indicated late 1980's. Same with the exhaust risers. What are you looking for concerning the age of these pieces?

    Summerwind,
    As for potential blockage in the OD I will verify with the marine shop that all passages are clear. They did tell me specifically that the impeller was in good shape. In fact they may have replaced it. One would think since they went throught the upper and lower gear cases they would have made sure water flowed unobstructed. I'll have to check flow again to be sure.

    Steve,
    On muffs (I assume you mean the thing we use to connect the hose to the OD, two rubber cups) she has never taken all the water the hose puts out, most of the water blows past onto the ground. I wonder if that is a difference between a Cobra and an 800. I guess that means I possibly have a flow problem.
    BTW, the OMC Cobra is newer and stronger than the OMC 800. I suppose that is how you can run more horses through it. I am not sure I can up size my motor with the 800 OD.

    What I did tonight;
    Pulled the power steering cooler for visual inspection. No blockages at all.
    Pulled the exhaust risers. Heavy corrosion but all seems intact. But, at the out end of the riser where the water jacket meets the exhaust tube I care fully chiseled away a lot of rust and scaled metal. There are notches cut into the end of the water jacket ring to facilitate water passage when it is connected to the rubber exhauat tube. When it is assembled it is like a perforation for water to escape past. I removed a lot of rust there. What do you guys think? could the problem be that simple? restricted water flow at that point? I am thinking I should pull the manifolds also since I am into this far.
    1979 Sea Ray Cuddy 260 Sundancer 5.7 OMC. Towed with 1999 F-350 Superduty 4X4. Portland, Oregon

  6. #6
    Join Date
    Apr 2008
    Location
    Delaware
    Boat
    Sea Ray
    Details
    1989 300 DA
    Engine(s)
    Twin 5.7 Merc Alpha I
    Posts
    1,570

    Re: 350 OMC over heating

    Um... if you had to chisel out the corrosion, I think you found your problem! If the risers and manifolds are that corroded, then its time to replace them both. They will restrict water flow and cause the overheating you described. Risers and manifolds are considered replaceable maint. items on a boat. If you can do the work yourself, the parts aren't overly expensive.
    1989 Sea Ray 300 Sundancer "Summer Quarters"
    Twin 5.7L carbed Mercruisers w/Alpha 1 Gen1
    Delaware Bay

  7. #7
    Join Date
    Aug 2009
    Location
    Oregon
    Boat
    Sea Ray
    Details
    1979 260 Sundancer Towed with 1999 F-350 4X4
    Engine(s)
    5.7 OMC 800
    Posts
    24

    Re: 350 OMC over heating

    Thanks Scorpio for the reply,
    I have to agree with you, heavy corrosion will restrict water flow and I suppose also retain heat. I'll see how expensive and how long to get the risers are at my local marine shop. Every thing is expensive on this OMC outdrive. I just spent $540 dollars on a simple mechanical shift cable. That is a parts price only! I am hating to find out what the risers will cost.

    I spent some time tonight cleaning what I could on the risers. I'll put them back on and see if there is improvement in the over heating problem.
    I also pulled the heat exchanger. It is going to get a good inspection and cleaning too.
    1979 Sea Ray Cuddy 260 Sundancer 5.7 OMC. Towed with 1999 F-350 Superduty 4X4. Portland, Oregon

  8. #8
    Join Date
    Apr 2008
    Location
    Delaware
    Boat
    Sea Ray
    Details
    1989 300 DA
    Engine(s)
    Twin 5.7 Merc Alpha I
    Posts
    1,570

    Re: 350 OMC over heating

    Do you have the old OMC log style manifolds? IF so you can convert to the Merc. style center riser manifolds with not too much trouble. Those units are cheaper and easier to find and they flow exhaust with less restriction than the log style, so you get some free horsepower. My old '82 was converted to Merc style and worked very well.
    1989 Sea Ray 300 Sundancer "Summer Quarters"
    Twin 5.7L carbed Mercruisers w/Alpha 1 Gen1
    Delaware Bay

  9. #9
    Join Date
    Aug 2009
    Location
    Oregon
    Boat
    Sea Ray
    Details
    1979 260 Sundancer Towed with 1999 F-350 4X4
    Engine(s)
    5.7 OMC 800
    Posts
    24

    Re: 350 OMC over heating

    Are they set up or can they be set up for freshwater cooling system? I might just go that route. Free horse power and new parts at similar cost, sounds great. I googled 'omc log manifold' and came up with "Go2marine.com". Ever heard of them?
    1979 Sea Ray Cuddy 260 Sundancer 5.7 OMC. Towed with 1999 F-350 Superduty 4X4. Portland, Oregon

  10. #10
    Join Date
    Apr 2008
    Location
    Delaware
    Boat
    Sea Ray
    Details
    1989 300 DA
    Engine(s)
    Twin 5.7 Merc Alpha I
    Posts
    1,570

    Re: 350 OMC over heating

    They can be set up for fresh water cooling. Haven't heard of that site but there are numerous online sites that carry aftermarket manifolds and risers, bot Merc style and OMC log style. I'm looking at a catalog now that lists OMC V8 log manifolds maed by BARR ( a good aftermarket name) OSCO also makes them, also a good name. I don't want to post websites as it may be against forum rules. PM me and I'll send some info to you.
    Chirs
    1989 Sea Ray 300 Sundancer "Summer Quarters"
    Twin 5.7L carbed Mercruisers w/Alpha 1 Gen1
    Delaware Bay

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