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Old 08-31-2010, 01:53 PM
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DavidMCX30 DavidMCX30 is offline
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Join Date: Jul 2010
Boat: 2002 MasterCraft X30
Location: Midwest
Posts: 84
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Originally Posted by ahhudgins View Post
I checked the manifolds on my 95 this summer because a poster had a similar question as yours. Using an infrared thermometer, the temperature varied at different points all over the manifolds and risers. My engine used the 143 degree thermostat (which I have since changed to the 160) and I got readings from 115 to 160 depending on exactly where I put the thermometer. Placing my hand on top of each riser, I can feel a little difference in the temperature. The only way to be 100% sure that you don’t have a blockage is to remove the riser and check. I’m not a big fan of the compressed air method. If there was a piece of old impeller in the manifold water jacket, blowing air into may have only moved it around.
Originally Posted by Cloaked View Post
I have had the same problem previously with the basic 351 engine.

One thing I learned from the fine folks at Discount Inboard Marine is their trick of the trade for testing the raw water pump for volume flow and, good impeller and housing integrity (wear plate and seals) is to get the engine running and rev it up to about 3k. Disconnect the thermostat end of the hose that comes directly out of the pump. It should fill a 5 gallon bucket in about 15 seconds. I tried this just this evening to see if it worked. Spot on for the 15 seconds, My pump is working fine. I have now eliminated that possibility of an issue I am dealing with. Saved me from rebuilding the pump unnecessarily. Good test. Next step now is to pull the riser from the mainfold and check the flow path there at the gasket. While the riser is off, I am replacing the exhaust hose going into the muffler. Those things are hard to replace without removing the riser. That 3" diameter hose is seriously stiff.
I think the marina did a similar test for me. They also put a clear hose on so they could see the water rate flowing through and to determine if there was too much air or other issues. I have to confess I'm fairly new to all of this, so I really have to rely on my mechanic and you guys at this point! Thanks for your insight.
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