Burned exhaust valves 5.7 GLi

[fisherman73]

I had been noticing a bit of a rough idle for awhile but didnt worry too much about it as it was slight. After this weekend the rough idle turned into a pretty good lope. I did some testing on it and discovered that I have burnt exhaust valves on #4 and #6 cylinders. The exhaust manifolds and risers were new about 7 years ago. I do run about half salt water and half fresh but I always flush with salt away after my salt water adventures. Questions are... is this a common issue with these ? Should i consider replacing the exhaust manifolds ? Are they typically the cause ? Anything else i should look for when I have it apart ?

My intake manifold is constantly rusting on the center runner. I get heavy rust flaking every time I clean it up and repaint it. Is there a life expectancy of the intake as well ? What about replacing it with aluminum ?

Are head, intake and valve cover gaskets the same for automotive applications or do I need to order specific marine gaskets ?

I know that is alot of questions for one post. Thanks for any input you can provide!

 

[Don S]

Re: Burned exhaust valves 5.7 GLi

is this a common issue with these ? Should i consider replacing the exhaust manifolds ? Are they typically the cause ? Anything else i should look for when I have it apart ?

No, it's not a common problem.
Check the manifold and riser, especially the gasket surfaces between the two. That is where they usually fail first.
Look for anything and everything as you take it apart.

 

[fisherman73]

Re: Burned exhaust valves 5.7 GLi

Thanks Don !

There is some rust flakes that are in one of the water passages between the riser and the manifold but the manifolds and risers look to be solid still. How long should I expect to be able to run them if I am diligent about flushing ? Any input on my other questions ?

 

[Don S]

Re: Burned exhaust valves 5.7 GLi

The manifolds will last until they fail. the gasket surfaces between the water and exhaust passages are the first place to fail.
Head gaskets need to be marine, others doesn't matter.