3.0 exhaust manifold over heats

[Ricky_rich]

I have a engine with the cooling system as in the picture.
A new exhaust manifold is installed, new impeller and new thermostat.
The engine it self is not running hot, only exhaust manifold getting to hot. I guess that affects carburetor and intake of gas/air, cause after running full throttle for a minute of two engine dies.
Have tried without thermostat but didn't help. I have a good flow of water from the raw water pump.
Is it possible that there could be something wrong between manifold and elbow that restricts water flow?

 

[Scott Danforth]

Marine engines have constant water flowing to the exhaust manifold.

Verify you have good water flow

 

[Ricky_rich]

Marine engines have constant water flowing to the exhaust manifold.

Verify you have good water flow

Yes that oss what I like to have. But if you look at the picture, there will only be a flow through the manifold when the thermostat is open. The constant flow that come from the bypass in the thermostat house connects after the elbow.
I think its a strange system. Would like to switch the hoses from thermostat house, but the are different sizes. Guess I can solve that part if needed. If I do that modification I get cold water from the impeller pump through manifold all the time, and warm water from open thermostat to go out after the elbow.

 

[ESGWheel]

While I am not familiar with these engines and their water flow, I will try to help. After looking at online pictures of this engine’s components, I agree that water only flows into the intake / exhaust combination manifold when the thermostat is open. However, there is constant water flow to the riser via the bypass as you pointed out.

I suspect the cooling effect of the fuel / air mixture passing thru the intake side of the combination manifold provides sufficient cooling to the unit until everything starts to warm up > then the thermostat opens and provides additional cooling to the manifold.

As to your issue of the manifold getting too hot and causing the engine to shut down:

• From reading your original post it seems as if you are having the engine die when running at full throttle and you are attributing that to a hot manifold. Correct? If yes, then the real issue is the engine is dying at full throttle, correct?

Need some additional information.

• Is this a new to you boat? Is this a new issue and last year, no issues? Are you experiencing the engine dying at full throttle when the boat is in the water or on a hose (muffs)? Can you do a compression test and post the numbers? Any other maintenance done?

From this additional information we should be able to start to figure this out….