Perkins 4108 Overheating
Bought a 1978 Cal 39 about two years ago, and the (Perkins 4108) engine coolant pump was frozen. The local mechanic changed the pump and it worked okay for docking and short motors. When we began using the motor for over a half hour, we noticed problems.
The temperature increases slowly all the way to the point where steam fills the cockpit (at about 190 degrees per the gauge). The transmission also gets quite hot.
This is what we’ve done:
1. We have removed the heat exchanger for inspection and it is pristinely clean. There is plenty of water coming out of the raw water exhaust. There is no water in the oil.
2. We also removed the rusted-out potable water heater recently but left those lines connected to a little heat exchanger that used to slide into the potable water heater. Should we plug or remove these lines?
3. We ran the engine, in gear, at the dock, at 800 rpm for 50 minutes and the temperature only went up to 140. No leaks/no steam.
4. Then yesterday we went for an engine check, motored at 1000 rpm for about an hour, and the temperature slowly and steadily rose to boiling with steam.
5. So, we removed the coolant reservoir. I was told there was supposed to be a thermostat located under the expansion tank, but when I pulled the tank off, there was no thermostat.
We have received divergent opinions from local marine mechanics about whether or not to replace the thermostat.
6. We read on another thread that the engine coolant water pump gaskets are of differing sizes - is it possible to verify proper gaskets without removing the pump to see if that's the problem?
7. The engine coolant is running through the dual engine oil and the transmission oil cooler. A local mechanic recommended plumbing this cooler with raw water. I'm wondering if the heat exchanger is big enough to handle this load, especially as we’ve read others with overheating 4108’s have solved their problem by replacing the original with a larger one.
8. We’ve also read threads about how air in the cooling system can cause overheating, but cannot find any bleed screw. Is it worth trying and if so, what would be the procedure.
FYI: Local water temperature: 79 degrees year-round for what that's worth