Overheat warning

Just bought a second-hand boat and used it for the 3rd time.


It got a 40HP Yamaha 2 stroke engine from 2013.


I anchored it for a few hours and when I started it to head home the overheat indicator started flashing. I was running it at low speed for a while and turned it off and on again but the indicator was still flashing.


I got towed back home since I did not want to risk anything.


When coming home I noticed that it's enough to turn on the ignition for the overheat warning to come on. Started it quickly to run it through with fresh water and the indicator kept flashing.




Since the warning comes on as soon as I turn on the ignition I suspect that it's a false indication. Cause even with some problems it would not overheat within a few seconds?


The water seems to be flowing as it should and it's not overly hot when coming out. As I understand it as long as the water flow keeps going I got water in the system? Correct?




Happy for any kind of input.

Images below shows engine ID & the warning on the tachometer.

Did you remember to mix oil with the fuel?

HugoBoater said:

Since the warning comes on as soon as I turn on the ignition I suspect that it's a false indication. Cause even with some problems it would not overheat within a few seconds?


The water seems to be flowing as it should and it's not overly hot when coming out. As I understand it as long as the water flow keeps going I got water in the system? Correct?

Click to expand...

In reference to your 2 statements above...

If when you start the engine it's cold, yet the overheat alarm activates, then yes I would suspect the issue is electrical. Pull the thermosensors and test they are within spec.

Yes, as long as you see water exiting the tell tale then there is water flowing through the cooling system. However, this does not imply water is completely circulating through the cooling system. Water will flow in the path of least resistance. If corrosion has built up enough within the cooling passages to cause blockage, this would prevent water from flowing...ect. The only true indicator the tell tale represents is whether or not the water pump is functioning...it is not an indication of whether or not water is flowing through the cooling system completely.

The first thing to check is that you had the right oil/fuel mix.
Then i would move onto making sure the cooling water is getting round the engine and is producing the tell tale.
As mentioned above, also pull the thermosensors out and check that they are all as they should be.
to be honest chances are that it is just electrical seeing as you don't even have to be running for this issue to occur.

It could possibly be a bad oil sensor. If the sensor is not working, it will send the warning because it thinks you are low on oil. It may also put the engine into a guardian mode and not allow you to run it at higher speeds. Not sure if this has happened to you, but just my 2 cents.

HugoBoater said:

J
I anchored it for a few hours and when I started it to head home the overheat indicator started flashing.

Click to expand...

Regarding the "low oil" issue - the OP says the Overheat Indicator flashed, not the Low Oil indicator. The oil level sensor and overheat sensor activate different flashing indicators on the Tacho.