Raw water cooled Yanmar - overheating?

[snowleopard]

One of my engines is giving an overheat warning when run on more than 1/2 throttle. The thermostat checks out - fully open at 52°C and the water flow appears to be as good as the other engine which is fine. The thermostat cuts off the bypass water as it opens the flow through the block so the water coming out of the exhaust has to have passed through the block.

Next suspect is the temperature sensor switch but how do I check it? I have the workshop manual which gives operating temperatures for the thermostat but not for the switch. I can try swapping the switches between the engines to see if the fault changes sides but I'd prefer to test it properly.

Anyone know where I can get the data?

 

[snowleopard]

B*gger. Google found it. 62°C

 

[Tony Cross]

How long have you been talking to yourself?

 

[Zagato]

A friend recently had this on a Yanmar 20 and pretty well stripped everything down before discovering it was worms blocking the water intake on the hull - worms seem to be a particular problem again in Chi this year...

 

[armchairsailor]

I take it your impellers are fine?

 

[Blueboatman]

Can't you just measure the engine block and ex manifold temperatures and compare them both at half revs but with one sounding the alarm, using the touch probe that comes with most digital multimeters these days?
Or is it infrequent and only when you are 'busy' under way?

 

[Marsupial]

One of my engines is giving an overheat warning when run on more than 1/2 throttle. The thermostat checks out - fully open at 52°C and the water flow appears to be as good as the other engine which is fine. The thermostat cuts off the bypass water as it opens the flow through the block so the water coming out of the exhaust has to have passed through the block.

Next suspect is the temperature sensor switch but how do I check it? I have the workshop manual which gives operating temperatures for the thermostat but not for the switch. I can try swapping the switches between the engines to see if the fault changes sides but I'd prefer to test it properly.

Anyone know where I can get the data?

Now you have the data you need to check the engines.

your first idea is the most practical

Just change the sensors over, the overheat condition should go to the other engine if the sensor is faulty

 

[DaveS]

One of my engines is giving an overheat warning when run on more than 1/2 throttle. The thermostat checks out - fully open at 52°C and the water flow appears to be as good as the other engine which is fine. The thermostat cuts off the bypass water as it opens the flow through the block so the water coming out of the exhaust has to have passed through the block.

Next suspect is the temperature sensor switch but how do I check it? I have the workshop manual which gives operating temperatures for the thermostat but not for the switch. I can try swapping the switches between the engines to see if the fault changes sides but I'd prefer to test it properly.

Anyone know where I can get the data?

I was going through this a couple of weeks ago, but without the benefit of a second engine to play "compare and contrast". I found an IR thermometer invaluable for looking at the different bits of the engine. HCl (B&Q brick & patio cleaner) sorted my overheating issue: 10 minutes of rapid fizzing then lots of crud came out when drained.