Well I finally was able to get this boat out for some test runs yesterday. There can be a lot of air in these systems so I expected that we might run into some issues. I wasn't disappointed. The good news was we got out and back OK, no leaks, blown hoses or anything, the 13 lb. pressure cap never released and at idle the engine was OK. The problems arose as soon as I pushed the throttle up to about 2000 RPM.
We had an infrared thermometer onboard so we could check the temperatures on the hoses manifold and exchanger. Thermostat is 160*. I drilled three 1/8" bypass holes in the thermostat in order to keep the coolant flowing during warm up so the manifolds wouldn't over heat. This appears to have worked out OK since she can idle all day with no issues.
FlowKooler 330-160 FlowKooler Robertshaw Series High Performance Thermostats | Summit Racing https://www.summitracing.com/parts/BRA-330-160
At low speeds, up to about 1000 RPM she stayed at 150 she would occasionally fluctuate up to about 175* or so. My thinking was that there were air pockets in the system working themselves out. I figured that later after she cooled down we'd find the coolant level low.
After we cleared the marinas no wake zone I decided to open her up a bit. That's when the problems started. At 2,000 to 3,000 RPM she immediately heated up to about 220* on the gauges. We checked this against the thermometer and the gauges were correct. So we shut her down for a few minutes and checked the engine over/ took some more temp readings. This is a full closed system including the manifolds. The exhaust risers were running in the upper 80* range. Mufflers nice and cool so no issues on the raw water side. None of the engine side hoses were over about 180* so we decided to start her up. Idling she cooled right down to about 150*.
Checking the hoses and fittings coming off of the exhaust manifolds we got readings of about 180*. After the coolant passed through the heat exchanger we were reading about 110*, this as the coolant came out of the exchanger heading back to the engine's water pump.
We brought her back to her slip and cleaned up while we waited a bit for her to cool off. She took about 1/2 gallon of additional coolant. I thought she's take a lot more.
After a meeting at the dock with a couple of skilled professionals we came up with the following:
#1: Bad thermostat. it's brand new but these things are known to happen. I did the check it on the kitchen stove after I drilled it out but who knows? The thinking was that the thermostat may not be opening fully or sticking. When she reaches 200+ the thermostat opens, we get an inrush of coolant. The thermostat then closes and sticks in that position until she goes through the cycle again. At low RPM the thinking is that the cooling demands are less and the thermostat is still sticking but the temperature oscillations aren't as great. Maybe I caused a problem by drilling it.
#2 Still some air in the system. I'm doubtful on this one.
I'll check her later today and see if adding the additional coolant makes any difference. I'm not expecting to fix this with a half gallon of coolant. If she acts the same I'll drain the system and replace the thermostat.
We'll figure it out.....
Thanks for reading.
MIA
