350 OMC over heating

[drtmnky]

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?

 

[Bodkin Creek George]

How old are your exhaust manifolds.
George

 

[Summerwind]

"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.

 

[stevea661]

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

 

[drtmnky]

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.

 

[SCORPIO]

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.

 

[drtmnky]

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.

 

[SCORPIO]

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.

 

[drtmnky]

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?

 

[SCORPIO]

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

 

[stevea661]

It appears to me from the picture you have the log style manifolds. It also appears from what I can see your manifolds are fresh water cooled. There is a block off gasket that goes between the riser and the manifold keeping the coolant and raw water seperated. Raw water comes into the bottom of the hear exchanger on the starboard side and exits on top on the same side, a hose runs off the top to a tee above the engine, where it splits the used raw water from the heat exchanger and it then ties into the bottom inlet side of each riser. As it goes up and over and out between the inner and outer jacket it cools the riser and then exits with the exhaust. The Raw water and the coolant don't mix, ever. Your exhaust manifolds should be good, but would be worth checking. Your heat exchanger could be a problem. Like I said in my last reply check the system with the IR gun at various point and you should be able to figure out whats going on.

 

[drtmnky]

:huh::huh::huh:

 

[drtmnky]

We had her out today for a few hours, she runs a lot better. I did a drive way test and after fooling around with the muffs for a while I finaly got water to pump through the OD. I guess the water pump needed priming. I am using double muffs that lightly squeeze onto the OD. Does anyone know of a better style?

At Idle she holds at about 170. At about 2000 rpm the temp climbs to about 175. At about 2300 rpm the temp goes north of 180.
From what I have read here above 180 is too hot.

I think I read in some other threads that high temp at high rpm indicates riser/manifold issues. Did I read correctly?

When I scrubbed the risers I was able to look closely at them and the manifolds. They are very worn and will have to be replaced before boating season next year. I have the original OMC log style manifold. I am strongly leaning to converting to center rise manifolds and risers. Scorpio says that is a good idea, what do you other guys think?