1989 carbed 454 temp issue

[alldodge]

I have the 496 manifolds/risers

The 496 cooling system is designed for closed cooling, your using raw water cooling. This could be the issue, not saying it is just the system is designed for different system water flow. The 496 system does not use restrictor gaskets between the manifold and the riser, so the water will not be able to stay full, if its not full the thermostat housing empties out some

 

[stinger222]

I swapped out the manifolds for the 496 style 8 years ago and the gauge used to register 160 all day long. Many guys with perf boats on Offshore Only.com forum have done the swap on older 454s and no one has ever mentioned this issue. Its like addl cold water is intruding the area where the sender is and causing the reading to be cool. When I removed the sending unit the other day to check it, water poured out everywhere( engine was not running. I wish the thermostat housing was clear plastic so I could see what is going on in there when the engine is running!!

 

[tpenfield]

You mentioned "40 hours on a 1989 454" . . . so I take it that this engine has been rebuilt? Any details on that? Did this situation start with the rebuild or was it good for a while after the rebuild? Any possibility that the wrong type of head gasket was installed? (serial vs. parallel flow)

Can you post a bunch of pictures of the engine, showing the various cooling hoses ?

If you have not backflushed and/or physically checked/cleaned the oil cooler, you could try that.

 

[stinger222]

The issue started after about 20 hrs on this engine.

 

[stinger222]

took the sending unit out of the thermostat housing, started the boat, water shooting out everywhere. clearly the sending unit is immersed in water. another guy posted on here a few years back and had similar symptoms and it ended up being a damaged circulation pump. This has me really stumped.

 

[alldodge]

It could be the circulation pump, doesn't take much to remove and check, just need new gaskets

 

[stinger222]

Another note, after driving around to warmup, bring it back down to idling around marina, temp gauge starts to race up to 160-180 range, then drops down to 120 in a few sec.
If I drive around at 1200 rpm or higher, gauge stays at 120, but if I bring it down to 800 rpm, I can get the gauge to jump up, but it comes back down after a few secs.
It always come back down, whether or not give more throttle, but it comes down right away if I give some more rpm.

 

[stinger222]

Update!!! Just took the circulation pump off. Removed back cover. impeller is split right down the middle!!! Problem finally solved. This was a GLM circ pump that I purchased about 4 years ago.

 

[tpenfield]

Nice find . . . don't usually see that as an issue, so I'm glad you found it. :thumb:

 

[alldodge]

Glad to hear, just like Fun Times use to say in his signature OEM parts are best (paraphrase)

 

[stinger222]

No Title

sort of leary about buying anymore GLM marine products. This was only after 30 hrs of usage in freshwater!!!

 

[tpenfield]

Interesting to see that. Essentially there was not much flow of water through the engine block, mostly at the thermostat housing and the exhaust manifolds, since that pump is what drives the circulation through the engine block.

 

[stinger222]

appreciate all the suggestions and help. .