Hi, that other thread about "The boat is floating again" is getting so long that I thought I'd start a new one.
Our 38' Commander has fresh water cooling, and we have had our port engine heating up more than the starboard. When on a slow cruise, the temperature of the expansion tank for the starboard engine runs about 180 degrees F, while on the port engine it runs about 210 degrees F. By the way, one of the first things we did was put new impellers in the raw water pumps.
We have been slowly going through all parts of the cooling system on the port engine. I had the engine heat exchanger out and opened up -- all is good there. I cleaned up the 2 psi relief valves controlling raw water coming out of the heat exchanger, and they are looking good. We back-flushed the engine oil and transmission coolers -- no evidence of any blockage there. I inspected various parts of the fresh water side -- the fresh water pump looks good, the coolant passages we could see all are clean, the thermostat opens when it should (as tested in a pot of water on the stove), the vee-belts are tight. We have been scratching our heads trying to figure out what the problem is.
The other day we decided to run a raw water pump output test. Using hose we directed the pump output into a 5 gallon bucket and measured the amount of water we got in 30 seconds with the engine at 1500 rpm. Then we did the same test to the starboard engine, with the engine at the same RPM. Turns out the port raw water pump was putting out about 30% less volume!
So we pulled the port raw water pump and looked it over. All seemed good. We decided to take it to a guy we know that is a marine mechanic to have a look at it. He took a little hook and reached up into the pump intake elbow, and pulled out a small handfull of pieces of rubber!
We had previously inspected the pump output passage assuming any broken impeller pieces would lodge there, but it didn't occur to us that they would be stuck in the pump intake side. Apparently someone had shredded an impeller sometime in the past by running it dry, and this mechanic told us that suprisingly often impeller pieces will somehow back up into the intake side of the pump.
Live and learn! Hopefully tomorrow we will get the pump reinstalled and see if we have eliminated or at least reduced our overheating problems.
1967 fiberglass 38' Chris Craft Commander Sportfisher with twin 427 CID 300 HP engines.