Westerbeke 4-91 or 30 overheat issue?

[DulceSuenos]

Bombay Clipper 31,
I have a low hour, great running westerbeke 4-91 if I run her over 1400 rpms she overheats I replaced the thermostat and it is worse. I checked the thermostat it doesnt open until 200 it is supposed to be 180. Without the stat it runs very close to the 180 mark where it is supposed to run. The cooling system appears very clean an dthe raw water pump is new and has a large strainer. I have seen somewhere that the 4-91 does not have a true mixing elbow but a pipe with the hose on it, and it wont get clogged like a different model or yanmar etc. Anyne familiar with these older 4-91's? Anyone know about the valve on the back of the motor (looks like a water faucet valve?)
Thanks!!!!

 

[RAD]

I'm very familiar with this great engine and the first question is what valve at the back of the motor? (pictures please), if you look in a Westerbeke manual it will show the water flow chart but basically if you have a water heater in line with the cooling hoses then there's the problem of air in the system and its a pain in the ass to get out but doable, have you done any work on the system where antifreeze was removed?
do you know about the bleeder valves on the engine? are you getting good salt water flow? have you looked inside the heat exchanger for clogs (cap on the end comes off)
tell me more and I'll try and help

 

[Bill Roosa]

check the hoses

The raw water hoses on the suction side my be collapsing while running

 

[RAD]

Or some of the raw water pump impeller vanes got into the oil cooler which is the first item on the output side of the pump and the flow is blocked

 

[DulceSuenos]

Ok I checked the oil cooler for blockage, looks good with a flashlight from what I can see. Raw water intake hoses are new when I installed a large seawater strainer , I removed the end cap on the exchanger and found some interesting things. My 3 month old Zinc Anode was completly mush and sitting on the floor of the chamber in pieces. What could cause this to go bad so fast, was it west marines quality issue?
Next I found the top 3-5 tubes clogged with some slimy corrosion, Can I run a hose thru the intatke sie of this and try to flush it and or use a vaccum to suck out the goo on the open side where I removed the cap?
Could just a few tubes clogged cause my engine to get too hot?
Without the thermostat in the coolant flow is not as fast as I would expect.

I think the water valve I am seeing was there for the old since removed water heater as it re routes and almost appears to go back to itself.

 

[RAD]

get a coat hanger or a piece of solid copper wire that fits in those tubes and clean them out as best you can and also squirt some water in there, I would check one system at a time, first check the raw water system for flow starting with disconnecting the hose at the exhaust elbow and see what kind of flow you have if good reconnect and then see if same flow is at exhaust outlet then if all this is good then check the fresh water side by making sure its full and all the air is out because that will cause an over heat. if you feel there's poor flow after checking every thing else then the fresh water pump could be the culprit but with such low hours I'd be surprised and any way that pump is an expensive one if you can find one you could always remove the thermostat and see how it does also so clean out the heat exchanger, check for flow in the salt water system and check for all air removal and flow
You said there was a hot water heater so that tells me that you have long hoses that leave the thermostat housing and return to the heat exchanger and thats a recipe for air in the system and if you have no hot water heater then just put a short hose from the thermostat to the heat exchanger