Overheating Westerbeake

Probably it's the T-stat

It's not clear to me from your post if you have good water flow from the exhaust or not. If you do (the flow looks normal) then the two most likely causes are a stuck thermostat or a clogged heat exchanger (coolant side). It's probably easiest to just replace the thermostat first. They will often open a little, but then get stuck. When you are not running the engine hard it will work just fine, but when you are at full cruising speed it will overheat. Sometimes they will work loose after a bit, but you should probably just replace it. If that doesn't do it, you may need to pull the heat exchanger ore and have it dipped at a radiator shop.

If you don't have good water flow and the strainer and impeller are okay (look at it closely), you could have a clogged heat exchanger core (saltwater side) or a partially blocked mixing elbow.

My money is on the thermostat. Good luck.

Where is the low flow? If it is on the raw water side, then the thermostat is not the problem. The thermostat is on the fresh water side of the system.

If you are not getting good raw water flow, that is a raw water issue:strainer, raw water pump, heat exchanger, exhaust elbow, plugged hose, plugged inlet seacock. When you took the cover off the water pump, did you crack the seacock a little to be sure you have free water flow? If you sucked a plastic bag up the inlet it will shut off water flow and cause overheating. You can probably guess how I know this. If it is a low raw water flow problem, for now confine your troubleshooting to the raw water side of the system.

I also have a 1985 westerbeke. If you have never cleaned out the heat exchanger you're way, way overdue. Frequent replacement of the pencil zinc is a good idea.

Regrettably, I've had both minor problems, 1) clogged raw water seacock with marine growth for the raw water side, and 2) cracked overflow tank hose for the coolant recovery tank ( in the lazarette, because of the in line water heater on the coolant side) which combined to raise the operating temperature without any apparent leak until I tired to fill the overflow tank from above and noticed the coolant dripping off the lower loop of the tank hose.

The actual crack in the hose was beneath the tank at the nipple (which again, is in the lazarette above the coolant tank and above the water heater) and dripped only the overflow to the shaft log rather than the engne compartment or bilge.

Clean the seacock from within with a bore brush to ensure adequate raw water flow and then check the coolant recovery system at or near your water heater.

Hope this helps. By the way, this is on a Universal 25XP ( actually the Kubota 950 3cyl block).

Overheating Westerbeke

I'm inclined to agree with your mechanic friend.

When my old, old, old Columbia had a raw water cooled Atomic 4 (one of the three that it did) I had to bypass the water heater coil from the engine because the salt water ate the aluminum circuit.

When I repowered with diesel, the Universal's dimensions required repositioning the new water heater that is served by the coolant system of the engine.

It obviously works best when the hot water tank is full ( providing, if you will, a larger heat exchanger in addition to the engine's three inch mounted exchanger.) However, that requires leaving the demand water pump on to keep the water heater full of water when under way. Sometimes the fresh water supply in the main tank is less than enough to keep the water heater full and consequently, it doesn't cool the engine circuit as much.I also don't like to leave the fresh water system "charged" with the pump when underway, since a leak or broken hose will drain the tanks into the bilge.

The mechanic who installed the 25XP was adamant that plumbing in the water heater required a extra coolant tank and overflow recovery system above the level of the water heater to increase the coolants efficiency.

It generally runs 165 degrees F if everything is fine. As I noted before, restriction in the raw water inlet and failure to recover the overflow current would increase the temperature to 190. Not catastrophic, but indicative of a problem.

Check the engine to water heater circuit and make sure the tank coil isn't the problem.If there's not enough water in the tank, the air will heat much faster than water.