454 Concern

"Have a 454/350 fresh water en

"Have a 454/350 fresh water engine. After starting the engine it takes a considerable amount of time for water to come out of the port exhaust vs. the starboard. Sometimes after starting and leaving engine at idle I hear a thump that sounds like cavitation. When I increase rpm's the noise goes away. While cruising at low rpm (1200) the port exhaust steams considerably. I have put a temperature gun on the engine at at all points it indicates 114-118 degrees. When the problem initially developed I checked the strainer and it was clean. I then opened the engines manifold drain ports and found a small amount of sand. Have rechecked drains and the water has no sand. Since initial sand removal, have run engine 50 hours at various rpm's with no changes. Getting ready to winterize, should I be concern about my observations? Any ideas as to what is causing my observations? Should I take some action before winterizing with antifreeze?"

What are the temperatures of B

What are the temperatures of BOTH manifolds?

Jeff

Use the boat on the Mississipp

Use the boat on the Mississippi. It has twin 454's. the port exhaust of the port engine takes an unusually long time to pump water of of the exhaust after starting. It can be expedited by increasing rpm's. This same exhaust developes steam when cruising from idle to 2000 rpm. The engine occassionally has a thumping noise while at idle cruise. I've put a thermal gun on all the exterior of the engine and get readings between 114-118 degrees. Both manifolds read basically the same. The readings on the Starboard engine read 114 to 118. The instrumentation reads about 120. There is no water in the oil.Thoughts? Should I be concerned winterizing with antifreeze?

"The "thumping" noise

"The "thumping" noise might be steam forming inside the manifold due to a blockage. I'd say it needs to come off and be looked at.

Definitely winterize it FIRST, and drain the exhaust system BEFORE removing anything or water will enter the rear cylinders.

Jeff

PS: Nice to see you use a lase temp gun! I'm a huge advocate of them for boaters."

"Do you have dripless packing?

"Do you have dripless packing? If you do, depending on where the water lines are connected, the heat exchanger may drain when you shut down. If the fitting is clogged on one engine, it will not drain the exahanger and therefore does not have to refill prior to dumping out the exhaust.

The other explaination could merely be a weak pump which does not perform properly at low speed.

The thumping noise could be noise in the gear or coupler which is not unusual, or bad flappers in your muffler. And as Jeff mentioned, it could be steam, provided the engine has run long enough to gererate that kind of heat.

Periodical manitenance requires you to replace the riser gaskets every couple years, along with the water pump. It may be a good time to do both.

Good luck
Rick"