coolant water level on Yanmar yr 2000 6LP-STE

[peterf]

after running at speed for about 45 mins or so as soon as i slow down the coolant water level light light and alarm comes on. As soon as I speed up both turn off. When I checked the level of the overflow bottle it was at the top and then the nxt morning back to the correct level. This has happened 2 days in a row.
Is there a sensor that could be defective?

Any help would be appreciated

[Tree]

Which engine?

[peterf]

6lp-ste yanmar

[Tree]

Ok, if I recall there is a sensor just below the filler cap. Without looking at the engine (it's almost midnight here) I can't confirm.

I'm sure RobS will be along to clarify as he is pretty hot on these engines

[peterf]

Thanks tree. I know the location of the coolant level sensor but I'm not sure if that is the problem. Why would the light and alarm shut off as I increased rpm. Is there a way to test if the sensor is defective? I was reading the only other post I could find on this subject and it turned out to be pin holes in the exhaust manifold cooling jacket and a very expensive repair. the post didn't say if the alarm went off at at high or low rpm.

[Pitou]

I'd pull the cap off of the engine once she's cooled down to make sure that your engine is full.

[Tree]

The sensor is up quite high isn't it? If so, what Kevin is saying makes sense and in fact something similar happened to my buddies boat after he changed his calorifier hoses - it only took about 2 pints of water but it was enough for the low level water alarm to sound.

[peterf]

First thing I checked. Filled right to the top. The first time it happened I added about 3/4 of a gallon to engine and filled the overfill to the proper level. Next day same thing happened when I would slow down. I will check again after running for awhile to check for a leak. All I did when I came back from the 2nd run was to check the overfill container and it had filled up to the top and the next morning back to normal.
Thanks for your help

[Tree]

Have you got a calorifier heated from the engine on the boat? Topping up may just be filling the header tank, but you may also be loosing water from a split hose somewhere. Bit difficult to explain, but have a look at the connections on the engine and on the hot water tank just incase they have split or showing signs of dry rot.

[peterf]

Thanks will do and let u know

[RobS]

Would be cheap and easy to change the pressure cap on the freshwater/coolant tank and change the thermostat.

Also, smell (don't taste) the hot water at one of the faucets. If you're heat exchanger element/coil within the water heater is leaking you wouldn't "see" a leak.

See attached for coolant level switch that triggers the alarm.

[peterf]

Thanks Rob. I had replaced the the cap first thing. I am not following you on smelling the hot water at the faucet. what am I looking for? How bout if I had the coolant system pressure tested? I wonder why it only happens at slow rpm and and stops as I speed up. I'm afraid I'm not much of a mechanic so am stumbling along and learning as I go

[Pitou]

Thanks Rob. I had replaced the the cap first thing. I am not following you on smelling the hot water at the faucet. what am I looking for? How bout if I had the coolant system pressure tested? I wonder why it only happens at slow rpm and and stops as I speed up. I'm afraid I'm not much of a mechanic so am stumbling along and learning as I go

Rob is suggesting that you check to see if the coolant is leaking into the fresh water in the hot water tank. The coolant runs through a loop inside your hot water tank heating the hot water. It's another possibility for coolant loss.

[RobS]

How bout if I had the coolant system pressure tested?

Yes for sure.

[peterf]

Thanks guys. Checked hot water at the sink no color or smell