Exhaust Manifold Heat Problems

[sr79]

1979 Sea Ray 268 with heat exchanger, engine temperature will not get below 190 degrees at 3000 RPM cruising speed. I have two different log style exhaust manifolds. Port side manifold has large water passage cross section where the starboard manifold has a small water passage cross section. Port side manifold temperature stays much cooler than the starboard side.

How do I fix this problem? Buy two new log manifolds with large or small water passages? Convert to center style manifolds? Do center style manifolds have less exhaust back pressure and do they perform better than log style? I'm getting ready to do something but not sure what to do, any suggestions?

 

[alldodge]

have two different log style exhaust manifolds.

This is an issue even if you were not running hotter. This will cause one head to be hotter then the other. A little hotter is ok

Port side manifold temperature stays much cooler than the starboard side.

Depends on how much hotter the one side is. A 10 to 15 degrees ok

Do center style manifolds have less exhaust back pressure and do they perform better than log style?

Most do because the opening is larger and the design

Your heat problem is probably due to your HE being clogged up, and/or the amount of water the impeller is moving. If any of the parts on the raw water side is causing a restriction, this will just add to the issue

Has the impeller been changed?

 

[sr79]

I thoroughly cleaned the heat exchanger tubes 2 years ago and installed new circulating water pump and sea water impeller. I now plan to check/change impeller again. Due to age of flapper valves in Y-tube I don't think there is any restrictions there, probably the flappers valves are gone. Also, I boiled out the manifolds with muriatic acid, that's when I noticed two different size water passages but didn't think it would make any difference. The "supposedly" rebuilt engine I install has 150-154 PSI compression but, now I'm wondering since it was sea water cooled is it possible that is has debris blockage in the water jacket. Thanks for all the above mentioned suggestions however, I may need some more ideas. Thanks you,

 

[alldodge]

Use a IR temp gun and measure the temps at the elbows, thermostat and some other ares. This will let you know where the flow is going

 

[Bondo]

The "supposedly" rebuilt engine I install has 150-154 PSI compression but, now I'm wondering since it was sea water cooled is it possible that is has debris blockage in the water jacket.

Ayuh,..... If there any debris in the block, it'll be found in 3 possible places,......

At the bottom of the block, by the block drains,.... 1 on each side,.....
Or,.....
Inside the heat exchanger, on the side ya can't clean,.....

 

[Scott Danforth]

is this a half system or a full system?

did the motor have the heat exchanger from day one, or is this something you added?

you mentioned boiling out the manifolds with muriatic acid. this would suggest a half system, however it could also mean that you added a heat exchanger to a used motor

if you added it to a used motor, most likely the glycol side of the heat exchanger is now plugged. there is no unplugging the glycol side. there is no way to clean out enough rust out of your old manifolds to use them with a heat exchanger. Always start with new manifolds. same goes with the engine

impeller needs to be replaced every few years period

center riser manifolds are a better design than the log manifolds

so, back to the first question, did the motor have the heat exchanger from day one, or is this something you added?

there is a reason you dont add a heat exchanger to a used motor. as indicated by Bondo and myself, you cant clean the glycol side.

 

[sr79]

Thank you for sharing your knowledge and experience, it really gives me a much better understanding of what might be happening. Answering your questions: The original motor was used with a heat exchanger but the replacement motor was used without a heat exchanger. Looking through the ports the heat exchanger tube bundle looked good, just a little green which I expect would be normal. Now, you suggest debris from the used engine block could be insulating the tube bundle, I suppose that could happen and I won't know until I take it off. The water passages of the manifolds cleaned up really good when boiled out. I used one original closed system manifold and one that came with the replacement motor, thus the two different sizes. The temperature difference between the two manifolds is a least 30 degrees, that's why I keep going back to the water volume difference in the two manifolds. Also, I installed a section of clear plastic tubing in the sea water line to the risers, looks like good flow and hot. That tells me heat exchanger is working. One more thing, original temp sending unit was mounted on a 4" extension T used to supply water to the cabin heater so temp reading was probably never accurate. I think this is getting too complicated for an average backyard boat mechanic....