496 Exhaust temp issues -

[txriverrat2001]

Working on a Baja w twin 496's - Showed up with all the exhaust hoses melted, etc.... Made all the repairs, rebuilt the seawater pump (impeller was good ... btw) with R&R's kit and test run yesterday.

The DDT says the manifolds are running in the 185 to 190 range @ 3500. The other motor is in the 120 range - which I consider normal.

The motor with the high exhaust temp also has over 35lbs of water pressure @ 3500.

The motor with the "normal" exhaust temps has 20lbs.

So there is a restriction possibly......

Does anyone have the water flow diagram on a 496?? What exactly do the hoses at the bottom of the manifold with the check ball in them do?? I suspect the ball is stuck or something is amiss here - but would appreciate any input.

Thanks
Capt Ross

 

[Raylar]

Sounds like you got a raw water system restriction as the pressure of 35 psi@ 3500 rpms is way to high Should only be about 35-30 psi at 5000 rpms.
Have you been boating in sandy or muddy water as you can clog up the exhaust manifolds with sand and debis, especially without a sand or sea water strainer. If the check ball drain back valves were bad and stuck closed they would not restrict flow and give a high manifold water temp and if they are bad and stuck open they would allow a good deal of raw water to bypass the manifold and cause a exhaust manifold heating condtion and melt your exhaust hoses as described.
Your Guardian system should be beeping and pulling back power at these manifold temps above about 160 degrees. Is you beeper or alarm sounding?

Hope this info helps your troubleshooting.

Best Regards,
Ray @ Raylar

 

[txriverrat2001]

Not sure where the guy has had the boat - I'm working on it. Had a broken up skeg and f'dup props that he told me he purchased it that way. Then a friend of his who I also work on his boat as well told me he did it on Travis Memeorial day - so I doubt the guy is gonna admit to runnin aground.

I'm gonna dig into the check balls - unfortunately no around here keeps that fitting in stock and every time I go to remove one to get to the ball they break.

 

[oceanoutlaw]

I think your on the right track with the check balls. 9 times out 10 i find the check ball clogged with salt. I find it more on the older aluminum manifolds verse the newer cast manifolds. The replacement check ball fittings are brass verse aluminum. and that seems to help too..good luck